Physics Classes

Author: Nayan Jha

  • Objective questions of magnetism and matter

    Objective questions of magnetism and matter

    Objective questions of magnetism and matter

    This assignment contains all type objective questions of magnetism and matter. it will be helpful for the students preparing for class 12th board examination or other competitive examinations like JEE/ NEET .

    Magnetism and matter

    1. With the tangent galvanometer it is desirable to have a deflection near 45°; then the percentage error:
    • (a)is less in the reading of deflection
    • (b)is negligible in the reading of deflection
    • (c)is less in the measurement of current
    • (d)is large in the measurement of current
    1. The sensitivity of a moving coil galvanometer depends on:
    • (a)the angle of deflection
    • (b)the earth’s magnetic field
    • (c)torsional constant of the spring
    • (d)the moment of inertia of the coil
    1. An ammeter can be converted into a voltmeter by connecting:
    • (a)a high resistance in series
    • (b)a low resistance in parallel
    • (c)a low resistance in series
    • (d)a high resistance in parallel
    1. In a moving coil galvanometer the deflection of the coil θ is related to the electric current I by the relation:
    • (a)I ꭀ tan θ       (b) I ꭀ θ                   (c) I ꭀ θ2                      (d) I ꭀ √θ
    1. A voltmeter of range 2V and resistance 300 Ω cannot be converted into ammeter of range:
    • (a)1 A      (b) 1 mA             (c) 100 mA              (d) 10 mA
    1. The effect due to uniform magnetic field on a freely suspended magnetic needle is as follows:
    • (a)both torque and net force are present
    • (b)torque is present but no net force
    • (c)both torque and net force are absent
    • (d)net force is present but not torque
    1. A voltmeter has a resistance of G ohm and range V volt. The value of resistance used in series to convert it into voltmeter of range nV volt is:
    • (a)nG       (b) (n – 1)G               (c) G/n                   (d) G/(n – 1)
    1. An ammeter has a resistance of G ohm and a range of I The value of resistance used in parallel to convert it into an ammeter of range nI amp is:
    • (a)nG       (b) (n – 1)G               (c) G/n               (d) G/(n – 1)
    1. To reduce the range of a voltmeter, its resistance need to be reduced. Which of the following resistance when connected in parallel will convert it into a voltmeter of range (V/n)?
    • (a)nR0 (b) (n + 1)R0     (c) (n – 1)R0        (d) None of these

    To download entire  assignment click here- Magnetism and matter objective

     

     

  • Objective questions of magnetic effect of current

    Objective questions of magnetic effect of current

    Objective questions of magnetic effect of current

    this assignment contains all important objective type  questions of  magnetic effect of current . Students preparing for 12th board examination or other competitive examination  like JEE/NEET.

    Before to solve objective questions of this chapter student may solve the objective questions of electric current. To download assignment of objective questions of electric current click here- 

    1. Magnetic induction is measured in:
    •  (a)weber (b) weber/m     (c) weber/m2      (d) weber/m3
    1. The force acting on a charge q moving with a velocity ʋ in a magnetic field of induction B is given by:
    • (a) q/(ʋ ₓ B) (b) (ʋ ₓ B)/q      (c) q/(ʋ ₓ B)         (d) (ʋ . B)q
    1. Two free parallel wire carrying currents in the opposite directions:
    • (a)attract each other
    • (b)repel each other
    • (c)do not affect each other
    • (d)get rotated to be perpendicular to each other
    1. Two parallel wires carrying currents in the same direction attract each other because of:
    • (a)potential difference between them
    • (b)mutual inductance between them
    • (c)electric forces between them
    • (d)magnetic force between them
    1. A free charged particle moves through a magnetic field. The particle may undergo a change in:
    • (a)speed  (b)energy   (c) direction of motion  (d) none these
    1. An electron and a proton travel with equal speeds and in the same direction, at 90° to a uniform magnetic field. They experience forces which are initially:
  • Objective questions of current electricity

    Objective questions of current electricity

    OBJECTIVE QUESTIONS OF CURRENT

    This topic provide important  objective questions for electric current it will be very important for the students preparing for class 12th board examination or JEE/NEET

    1. For which of the following dependence of drift velocity ʋ on electric field E is ohm’s law obeyed?
    • (a) ʋ ꭀ E (b) ʋ = constant              (c) ʋ ꭀ E1/2              (d) ʋ ꭀ E2
    1. in metals the time of relaxation of electrons:
    • (a)increases with increasing temperature
    • (b)decreases with increasing temperature
    • (c)does not depend on temperature
    • (d)changes suddenly at 400 K
    1. Constantan wire is used for making standard resistance because it has:
    • (a)low specific resistance
    • (b)high specific resistance
    • (c)negligible temperature coefficient of resistance
    • (d)high melting point
    1. A potential difference is applied across the ends of a metallic wire. If the potential difference is doubled, the drift velocity:
    • (a)will be doubled                               (c) will be quadrupled
    • (b)will be halved (d) will remain unchanged
    1. The maximum current that flows in the fuse wire, before it blow out, varies with the radius r as:
    • (a)r3/2      (b) r                                   (c) r2/3                    (d) r1/2
    • To download entire questions paper click here-click here electric current objective questions
  • Objective questions of atoms and nuclei

    Objective questions of atoms and nuclei

    This assignment contain all important objective questions of atoms and nuclei , which is important for the students preparing for board examination and other competitive examinations .

    Atomic Structure

    1. According to Bohr’s atomic model:
      (a)an atom has heavy, positively charged nucleus
      (b)the electron radiates energy only when it jumps to another orbit
      (c)the electron can move only in particular orbits
      (d)all the above statements are correct

     

    1. In an atom, two electrons move around the nucleus in circular orbit of radii R and 4R. The ratio of the time taken by them to complete one revolution is:
      (a)1/4            (b) 4/1                              (c) 8/1                            (d) 1/8

     

    1. According to Bohr’s quantum condition, an electron can revolve only in those orbits in which:                 
      (a) its energy is an integral multiple of h/2π
      (b) its linear momentum is an integral multiple of h/2π
      (c)  its angular momentum is an integral multiple of h/2π
      (d) its angular momentum vector is perpendicular to magnetic dipole moment vector

     

    1. According Bohr’s theory the radius of the electron in an orbit described by principal quantum number n and atomic number Z is proportional to:                                                                                   
      (a)Z2n2
       (b) Z2 /n2
      (c) Z2 /n
      (d) n2 /Z

     

    1. When the electron jumps from a level n = 4 to n = 1, the momentum of the recoiled hydrogen atom will be:                             
      (a)5 ₓ 10-27 kg – ms-1
      (b) 13.6 ₓ 10-19 kg – ms-1
      (c)75 ₓ 10-19 kg – ms-1
      (d) zero

     

    1. The radius of Bohr’s fast orbit is a0. The electron in nth orbit has a radius:
      (a)na0
      (b) a0/n
      (c) n2a0
      (d) a0/n2

     

    1. The angular momentum of an electron in the nth orbit is given by:
      (a)nh
      (b) h/2πn
      (c) nh/2π
      (d) n2h/2π

     

    1. When a hydrogen atom is raised from the ground state to fifth state:
      (a)both KE and PE increase
      (b) PE increases and KE decreases
      (c)both KE and PE decrease
      (d) PE decreases and KE increases
    2. As the electron in Bohr orbit of hydrogen atom passes from state n = 2 to n = 1, the KE (K) and PE (U) change as:                                  (a)K two-fold, U also two-fold     
      (c) K four-fold, U two-fold
      (b)K four-fold, U also four-fold
      (d) K two-fold U four-fold
    3.  An electron jumps from the 4th orbit to the 2nd orbit of a hydrogen atom. Given the Rydberg constant R = 105 cm-1, the frequency in Hz of the emitted radiation will be:                         
      (a)3/16 ₓ 105
      (b) 3/16 ₓ 1015
      (c) 9/16 ₓ 1015
      (d) 3/4 ₓ 1015 
    4.  Nitrogen gas, cynogen gas and compounds of carbon give band spectra because:
      (a)these are excited in molecular state
      (b)these are in atomic state
      (c)these are inorganic compounds
      (d)these are in gaseous state
    5.  The hydrogen atom can give spectral lines in the series, Lyman, Balmer and Paschen. Which of the following statements is correct?                                                                                                 
      (a)Lyman series is in the infrared region
      (b)Balmer series is in the visible region (partly)
      (c)Balmer series is solely in the ultraviolet region
      (d)Paschen series is in the visible region
    6. .Which of the following statements is true regarding Bohr’s model of hydrogen atom?                                                               
      (a)Orbiting speed of electron decreases as it falls to discrete orbits away from the nucleus.
      (b)Radii of allowed orbits of electrons are proportional to the principal quantum number.
      (c)Frequency with which electrons orbits around the nucleus in discrete orbits is inversely proportional the principal quantum number.
    7. Binding force with which the electron is bound to the nucleus increases as it shifts to outer orbits.

      (A)a and    c
      (B)   b    and    d
      (C)   a, b   and   c
      (D)   b, c   and   d
    8.  An electron in the hydrogen atom jumps from excited state n to the ground state. The wavelength so emitted illuminates a photosensitive material having work function 2.75 eV. If the stopping potential of the photo-electron is 10 V, then the value of n is:
      (a)2                 (b)   3            (c)  4                   (d)   5
    9.  In Bohr’s model, the atomic radius of the fast orbit is r0;then the radius of the third orbit is:
      (a)r0/9                        (b)  r0                 (c) 9r0                              (d) 3r0 
    10.  The ground state energy of H-atom is 13.6 eV. The energy needed to ionise H-atom from its second excited state is:       (a)51 eV       (b) 3.4 eV               (c) 13.6 eV              (d) 12.1 eV
    11. Hydrogen atoms are excited from ground state to the state of principal quantum number 4. Then, the number of spectral lines observed will be:                 
      (a) 3       (b)  6        (c) 5           (d)  2
    12. If an electron in n = 3 orbit of hydrogen atom jumps down to n = 2 orbits, the amount of energy released and the wavelength of radiation emitted are:
      (a)85 eV, 6566 Å (b) 1.89eV, 1240 Å        (c) 1.89 eV, 6566 Å   (d) 1.5 eV,6566 Å
    13.  The longest wavelength that a single ionised helium atom in its ground state will absorb is:       
      (a)912 Å            (b) 304 Å              (c) 606 Å            (d) 1216 Å
    14.  If the ionisation potential of hydrogen atom is 13.6 eV, the energy required to remove the electron from the third orbit of hydrogen atom is:                 
      (a)5 V          (b) 1.5 eV          (c) 4.5 eV         (d) 3.4 V
    15. The ratio of the areas within the electron orbits for the first excited state the ground state for the ground state for the hydrogen atom is:(a)2 : 1 (b) 4 : 1    (c) 8 : 1    (d) 16 : 1
    16. The first excitation potential of the hydrogen atom in the ground state is:
      (a)6 volt (b) 10.2 volt (c) 3.4 volt     (d) 1.89 volt
    17. The minimum energy in electron volt required to strip a ten times ionized sodium atom ( i.e., Z = 11) of its last electron is:
      (a)6 eV        (b) 13.6/11  eV    (c) 13.6 ₓ 11 eV      (d) 13.6 ₓ (11)2 eV
    18.  Of the following transitions in hydrogen atom, the one which gives emission line of minimum frequency is:(a)n = 1 to n = 2   (b) n = 3 to n = 10        (c) n = 10 to n = 3        (d) n = 2 to n = 1
    19. The energy of an electron in the nth orbit of positronium is:
      (a) -13.6/n2 eV (b) -13.6 ₓ 2/n2 eV       (c) -13.6 ₓ 4/n2 eV        (d) -13.6/2n2 eV
    20. The ratio (in SI units) of magnetic dipole moment to that of the angular momentum of electron of mass m kg and charge e coulomb in Bohr’s orbit of hydrogen atom is:
      (a) e/2m (b) e/m             (c) 2e/m        (d) none of these
    21.  The Bohr model of atoms: 
      (a)assumes that the angular momentum of the electrons is quantized
      (b)uses Einstein’s photoelectric equation
      (c)predicts continuous emission spectra for atoms
      (d)predicts the same emission spectra for all types of atoms
    22.  The angular momentum of an electron in a hydrogen atom is proportional to:
      (a)1/√r         (b) 1/r          (c) √r           (d) r2 
    23.  What will be the angular momentum in fourth orbit, if L is the angular momentum of the electron in the second orbit of hydrogen atom? 
      (a)2 L (b) 3/2 L     (c) 2/3 L      (d) L/2
    24.  The required energy to detach one electron from Balmer series of hydrogen spectrum is:     
      (a)6 eV        (b) 10.2 eV           (c) 3.4 eV    (d) -1.5 eV
    25.  Which of the following is quantised according to Bohr’s theory of hydrogen atom?       (a)Linear momentum of electron
      (b)Angular momentum of electron
      (c)Angular velocity of electron
      (d)Linear velocity of electron
    26. The energy levels of a certain atom for 1st ,2nd and 3rd levels are E, 4E/3 and 2E respectively. A photon of wavelength λ is emitted for a transition 3 →1.What will be the wavelength of emission for transition 2 → 1?     
      (a) λ/3       (b) 4λ/3       (c) 3λ/4              (d) 3λ
    27. The ratio of the frequencies of the long wavelength limits of the Lyman and Balmer series of hydrogen is: 
      (a)27 : 5 (b) 5 : 27    (c) 4 : 1    (d) 1 : 4
    28. If electron in a hydrogen atom has moved from n = 1 to n = 10 orbit, the potential energy of the system has: 
      (a)Increased       (b)Decreased         (c) remains unchanged      (d) become zero
    29. The energy of hydrogen atom in nth orbit is En , then the energy in nth orbit of singly ionised helium atom will be:     
      (a)4En     (b) En/4                 (c) 2En                      (d) En/2
    30. The energy of hydrogen atom is -13.6 eV in the first orbit, then calculate the energy of He atom in the same orbit:   
      (a)6 eV        (b) -27.2 eV            (c) -54.4 eV           (d) +54.4 eV
    31.  In hydrogen spectrum, the shortest wavelength in Balmer series is λ. The shortest wavelength in Brackett series will be:(a)2λ        (b) 4λ                            (c) 9λ                               (d) 16λ
    32. The ratio of the largest to shortest wavelength in Lyman series of hydrogen spectra is:   
      (a) 25/9  (b) 17/6 (c) 9/5 (d) 4/3
    33. The minimum orbital angular momentum of the electron in hydrogen atom is: 
      (a) h             (b) h/π                      (c) h/2π                       (d) h/2
    34. The total energy of an electron in the first excited state of hydrogen atom is about – 3.4 eV. Its KE in this state is:
      (a)4 eV (b) 6.8 eV                      (c) -3.4 eV                       (d)-6.8 eV
    35. The ground state energy of hydrogen atom is -13.6 eV. What is the potential energy of the electron in this state?
      (a)0 eV (b) -27.2 eV                  (c) 1 eV                            (d) 2 eV
    36.  If λ1 and λ2 are the wavelengths of the first member of the Lyman and Paschen series respectively, then λ1 : λ2 is:   
      (a)1 : 3 (b) 1 : 30                       (c) 7 : 50                           (d) 7 : 108

     

     

  • Objective questions of wave optics

    Objective questions of wave optics

    Objective questions of wave optics

    diffraction central maximum

    Student’s as we know  from this  year , in CBSE 12th board examination ( physics )  there will be 20 , 1- mark questions . therefore we just posted some  objective questions of wave optics , so that students can practice well all kind of objective questions of wave optics   in short time .

    Objective questions of wave optics

    1. Newton has postulated his corpuscular theory on the basis of , (a) Newton’s ring (b) color due to thin film (c) dispersing of light (d) rectilinear propagation of light.
    2. The wavefront is a surface in which ; (a) all points are on the same phase(b) there are pair of points in opposite phase (c) there are pairs of points with phase difference 900 (d)there are no relation between the phase.
    3. The concepts of secondary wavelets from all points on a wave front was proposed by ; (a) Newton (b) Huygen (c) Faraday (d) Raman.
    4. Huygen’s concepts of secondary waves ; (a) allow us to find the focal length of  thin lens  (b) gives the magnifying power of thin lens (c) is a geometrical method to find the wavelength (d)is used to find the velocity of light.
    5. For constructive interference to take place between two monochromatic light waves of wavelength λ , the path difference should be ; (a) (2n-1)λ/4 (b) (2n-1)λ/2 (c) nλ (d)(2n+1)λ/2
    6. Two light sources are coherent when ; (a) their amplitudes are equal (b) their frequency are equal (c) their wavelengths are equal (d)their frequencies are equal and their phase difference is constant.
    7. Ratio of intensity of two waves is given by 4:1 , the ratio of amplitudes of their waves is ; (a) 2:1 (b)1:2 (c) 4:1 (d)1:4
    8. If the ratio of intensities of two waves causing interference be 9:4 then the ratio of the resultant maximum and minimum intensity will be : ; (a) 9:4(b) 3:2 (c) 25:1 (d)5:1 .

    TO SOLVE IMPORTANT QUESTIONS ( THEORY AND NUMERIALS)-CLICK HERE

    1. In young’s double slit experiment , if monochromatic light used is replaced by white light , then ; (a) no fringes are observed (b) all bright fringes becomes white (c) all fringes have colour between violet and red  (d)only central fringes is white and all other fringes are coloured .
    2. Two coherent monochromatic light beams of intensity I and 4I are superposed , the max and min. possible intensities in the resulting beam are  ; (a) 5I and I (b) 5I and 3I (c) 9I and I (d) 9I and 3I
    3. If two waves , each of intensities I0 , having the same frequency but differing by constant phase angle of 600 , superpose at a certain point in space , then the intensity of resultant wave is ; (a) 2I0 (b) √3 I0 (c) 3I0 (d) 4I0
    4. Two monochromatic waves each of intensity I , have constant phase difference of ɸ , if these waves superpose , then the intensity of resulting wave is  ; (a) 4I (b) 4Icosɸ (c) 4Icos2ɸ (d) 4I cos2 (ɸ/2)
    5. Two monochromatic waves of same amplitude ‘a’ ,have random phase difference between them . when these wave superpose , then the amplitude of resulting wave is given by ; (a) √2a  (b) 2a (c) 4a (d)zero .
    6.  The contrast in the fringes in any interference pattern depends on ; (a) fringe width (b)wavelength (c) intensity ratio of the sources (d) distance between the sources
    7. In young’s double slit experiment if the distance between the slits is made 3-folds, the fringe width becomes ; (a) 1/3 folds (b) 3 folds (c) 1/9 folds (d) 9 folds .
    8. In Young’s double slit experiments the separation between the is halved and separation between the slits and screen is doubled , the fringe width is ; ; (a) unchanged (b) halved (c) doubled (d) quadrupled .
    9. Yellow light emitted by sodium lamp in Young’s double slit experiment is replaced by blue light of the same intensity ; (a) fringe width will decrease (b) fringe width will increase (c) fringe width will remain unchanged (d) fringe will become less intense .
    10. Two light waves are coherent if they are obtained from a single monochromatic source by ; ; (a) division of amplitude only (b) division of wavefront only (c) both of the above (d) none of the above.

    TO SOLVE IMPORTANT QUESTIONS OF RAY OPTICS – CLICK HERE

    1. In an interference experiment monochromatic light is replaced by white light , we will see , ; (a) uniform illumination on the screen (b) uniform darkness in the screen (c) equally spaced white and dark bands (d) a few coloured bands and then uniform illumination .
    2. In Young’s double slit experiment the fringe width is found to be 0.4 mm . if the whole apparatus is immersed in water of refractive index 4/3 without disturbing the original geometric arrangement , then new fringe width will be ; (a) 0.3mm (b)0.40mm  (c) 0.53mm (d )450 microns .
    3. Two waves are said to be coherent if they have ; (a) same wave length (b) same amplitude (c) same amplitude and save wavelength (d) same wavelength and constant phase difference .
    4. In a young’s double slit experiment fringe width is equal to 1mm , then the distance of the nearest bright fringe from the central fringe will be ; (a) 1mm (b) 0.5mm (c) 2mm (d) insufficient data ,
    5. In young’s double slit experiment . if width of the slit s is increased keeping other parameters constant , then the interference fringes will be ; (a) remain unchanged (b) form closer (c) form further away (d) gradually disappear.
    6. Interference of light waves from two coherent sources is possible for ; (a) unpolarised light waves only (b) polarised light waves only if their polarisation is in the same direction (c) both of the above (d) none of the above.
    7. Two waves coming from two coherent sources , having different intensity interfere , their ratio of maximum intensity is 25 , then the intensities of the sources are in the ratio ; (a) 25:1 (b) 25:16   (c) 9:4  (d) 5:1 .
    8. When petrol drop from a vehicle fall over rain water on the road , colors are seen because of ; (a) dispersion of light (b) scattering of light (c) interference of light (d) absorption of light.
    9. In one of the two slits of young’s double slit experiment is painted over so that it transmits half the light intensity of the other , then ; (a) the fringe system will disappear (b) the bright fringe will be more bright (c) the dark fringe will be brighter and vice -versa (d) none of the above .
    10. The phenomena of diffraction can be exhibited by ; (a) polarised wave only (b) unpolarised wave only (c) longitudinal wave only (d)all kind of wave
    11. Diffraction effects are easily observed for ; (a) microwave (b) sound wave (c) radio waves (d) all of the these .
    12. In case of diffraction at single slit if the wavelength of light becomes equal to the aperture of slit , on the screen we shall observe : ; (a) image of slit (b) diffraction band (c)uniform illumination (d) non-uniform illumination.
    13. Light of wavelength 2 x 10-3 m falls on a slit of width 4 x 10-3 m . the angular dispersion of the central max will be ; (a) 300 (b) 600 (c) 900 (d) 1800 .
    14. The width of the diffraction band varies as (a) inversely as the wavelength (b) directly as the width of the slit (c) directly as the distance between slit and the screen (d) inversely as the size of source from which the slit is illuminated .
    15. The polarisation of light prove the ; (a) corpuscular nature of light (b) quantum nature of light (c) transverse wave nature of light (d) longitudinal wave nature of light .
    16. A beam of light strikes a piece of glass at an angle of incidence of 600 and reflected beam is completely plane polarized , then the refractive index of glass is  ; (a) 1.5 (b) √3 (c) √2 (d) 2/3.
    17. A ray of light incident on the surface of a glass plate at an angle of incidence equal to Brewster’s angle ɸ. If µ is the refractive index of the glass then the angle between reflected and refracted rays is ; (a) (90+ɸ) (b) sin-1 (µ cosɸ) (c) 900 (d) sin-1( sinɸ/µ).
    18. A Nicol prism is based on the principle of ; (a) refraction (b) scattering  (c) dichroism (d) double refraction .
    19. Which of these wave can be polarised ? (a)sound wave (b) longitudinal wave on a string (c) transverse wave on a string (d) light wave
    20. Two Nicol prism are first crossed and ten one of them is rotated through 600 , the percentage of incident light transmitted is ; (a) 1.25 (b)25 (c)37.5 (d)50 .
    21. Two polaroids are placed cross to each other , now one of them is rotated through an angle of 450 the percentage of incident light now transmitted through the system is (a)15% (b)25% (c) 50% (d) 60% ( e) 75%.
    22. Waves can’t be polarised is ; (a) light wave (b) electromagnetic wave (c) transverse wave (d) longitudinal wave .
    23. Young’s double slit experiment is made in a liquid . The tenth bright fringe in the liquid lies where the 6th bright fringe lies in the vacuum . The refractive index of the liquid is approximately ; (a) 1.8 (b) 1.54    (c) 1.67     (d)    2      .
    24. If light is polarised by reflection , then the angle between reflected and refracted light is ;  (a) Π     (b) Π/2    (c) Π/3      (d) Π/4
    25. A beam of light strikes a piece of glass at an angle of incidence of 600 and the reflected ray is completely polarised . Then the refractive index of the glass is ;  (a) 1.5   (b) √3    (c) √2  (d)3/2
    26. What does not change on polarisation of light ;  (a) intensity (b) phase (c) frequency (d) wavelength                                                                                                  TO SOLVE OTHER IMPORTANT QUESTIONS OF WAVE OPTICS – CLOCK HERE
  • Diffraction of light

    Diffraction of light

    Diffraction of light

    What is diffraction of light ? conditions for maximum and minimum using single slit experiment, and intensity curve .

    Diffraction of light  –

    When a beam of monochromatic light passes through an aperture or an obstacle comes into the way of light then light is bent at the corners of the aperture or obstacle , this phenomena of light is called diffraction of light

    Diffraction of light at a single slit – when a beam of monochromatic light is made incident on single slit , then we get  diffraction pattern on the screen , which contain bright (maximum) and dark (minimum) band .

    diffraction single slit

     

    Let, AB be a slit of width ‘a’ and parallel beam of a monochromatic light incident on it . All the primary ray incident converges at the center and form a bright fringe, and all the secondary wave gets superimposed and form secondary dark and bright fringes on the screen .

    Let θ be the angle of diffraction  for waves reaching at point P of screen , and AD is the perpendicular drown from ‘A’

    The path difference   between the rays AP and BP

    So path difference , p =   BP – AP = BD

    But from geometry <ANB = θ

    Sinθ= BD/AB ,

    Or,   BD = AB sinθ

    width of the slit AB = a

    Hence path difference ;  p = a sinθ  ……………………………(i)

    Position of central maximum  – the wavelets fall on the lens L along parallel direction of the axis reaches at o in the same phase and form central maximum .

    Position of secondary minimum  –   if we imagine the slits is divided in two equal halves  AC and CB then every point on the upper half the path difference is λ/2  and same as in lower half . they will reach at the point p in opposite phase and form destructive  interference cause of minimum or dark band , for dark band   a sinθ =  nλ  , where  n= 1,2,3,4………..

    , if θ is very small then , aθ = nλ

    So , θ = nλ/a  .

    Position of secondary maximum  –   we imagine slits is divided in three equal parts so the path difference between these two upper parts will be λ/2 , which will cancelled each other effect , so only third part will be the cause of the diffraction pattern obtained on the screen .

    So ,    a sinθ    = ( 2n+1) λ/2

    If     θ is very small then ,      a θ  =    ( 2n+1) λ/2

    So ,            θ =( 2n+1) λ/2  / a

     

    Intensity- position curve for diffraction of light

    intensity curve

    FOR IMPORTANT QUESTIONS OF RAY OPTICS– CLICK HERE

     

    Central maximum is twice the width of any other secondary maximum –

     

    diffraction central maximum

    For first minimum , from the relation of secondary minimum     θ = nλ/a

    Here value of n=1 ( for first minimum ) , so,  θ = 1λ/a  .

    But  , according to the geometry  θ = y1 / D ( where D is the separation between the slit and screen ) .

    Angular width of the central maximum           2θ = y1 + y2  /D ,

    Or,          2λ/a =  y1+ y2 /D,

    Or ,     Y1 + y2 = 2λD/a

    Therefore , width of the slits = 2( λD/a) = 2  x (width of other secondary maximum).

    Questions based on diffraction of light  – What do you mean by the term diffraction of light ? using single slit show the conditions of central maximum, secondary minimum, secondary maximum and hence draw the intensity curve with position ‘x’ . Using single slit experiment show that (i) the intensity of diffraction fringes increases as order (n) increases .(ii) angular width of the central maximum is twice of first order secondary maximum .

    For important questions based on the chapter wave optics– click here

     

    FOR IMPORTANT QUESTIONS OF DUAL NATURE OF RADIATION AND MATTER- CLICK HERE

  • Important questions of system of particles and rotational motion

    Important questions of system of particles and rotational motion

    Important questions of system of particles and rotational motion

    In this assignment we are providing for the students, Important questions of system of particles and rotational motion . Students who is already   completed the theory and derivation of entire  chapter should solve all the questions given in this assignment ” Important questions of system of particles and rotational motion”. Since numbers  of questions in this assignment is very less, so   it can be revised or solved in very short time .

    System of particle and rotational motion

    assignment

     

    1. Is it possible to open a pen cap with one finger? Why?
    2. When a sphere, ring, disc and spherical shell are coming down on an inclined plane, rolling without slipping, which will reach the ground first?
    3. How will you distinguish between a hard-boiled egg and a raw egg by spinning each on a table top?
    4. Find the torque of a force 7î-3jˆ-5kˆ about the origin which acts on a particle whose position vector is iˆ+jˆ-kˆ.
    5. What is torque? Write its formula in vector form. Handle, to open the door, is always provided at the free edge of a door. Why?
    6. Establish the relation between angular momentum and rotational kinetic energy?
    7. If earth were to shrink suddenly, what would happen to the length of the day?
    8. Derive the relations
    • L = I ω (ii) Ʈ =  Iα
    1. If angular momentum is covered in a system whose moment of inertia is decreased, will its rotational kinetic energy to be also conserved? Explain.
    2. Can a body in translatory  motion have angular momentum? Explain.
    3. A ring, a dice and a sphere all of the same radius and same mass roll down on an inclined plane from the same height h. Which of the three reaches the bottom

    (i)earliest             (ii) latest   ?

    1. Write an expression for the moment of inertia of a circular disc of a mass M and radius R

    (i)about an axis passing through its center, and a perpendicular to its plane.

    (ii) about its diameter.

    (iii)about a tangent to its own plane.

    (iv) about a tangent perpendicular to the plane of the disc.

    1. How much fraction of the K.E. of rolling is purely (i) translational (ii) rotational ?
    2. Obtain an expression for position vector of center of mass of a two particle system.
    3. What is the difference between rotational kinetic energy and rolling kinetic energy?

    Show that rolling kinetic energy of a rolling body is given by 1/2mv2(( K2/r2)+1) , where r is the radius of the body and K is the radius of gyration of the body.

    1. (i) Define moment of inertia. Write the parallel and perpendicular axis theorem.
    • Derive an expression for moment of inertia of a disc of radius r, mass m
    1. Prove that the rate of a change of the angular momentum of particle is equal the torque of acting on it.
    2. Define moment inertia. Write any two factors which it depends. When the diver leaves the diving board, why does he bring his hand and feet closer together in order to make a some result ?
    3. Derive an expression for moment of inertia of a thin circular ring passing through the centerrotational motionr and perpendicular to the plane of the ring.
    4. (I)Define moment of inertia .write the parallel and perpendicular axis theorem .(II)derive an expression for moment of inertia of a disc of radius r , mass m about the axis along its diameter.
    5. A rope of negligible mass is wound round a hollow cylinder of mass 3kg and radius 40cm . what is the angular acceleration of the cylinder if the rope is pulled by a force of 30N?what is the linear acceleration of the rope?
    6. From a uniform circular disc of diameter d , a circular hole of diameter d/6 and having its center at a distance of d/4 from the center of the disc is scooped out , find the center of mass of the remaining portion .
    7. A uniform ring of mass 10kg and diameter 0.40m rotate with the uniform speed of 2100 rpm, find the moment of inertia and angular momentum of the ring about its geometric axis
    8. A cylinder of mass 5kg and radius 30cm and free to rotate about its axis , receive an angular impulse of 3kg m2/s followed by a similar impulse after every 4 sec . what is the angular speed of the cylinder 30 sec. after the initial impulse ? the cylinder is at rest initially.
    9. Two particles of mass 2kg and 1kg are moving along the same line with speeds 2m/s and 5m/s respectively . what is the speed of the center of mass of the system if both the particles are moving (a) in the same direction (b) in opposite direction ?

     

    TO SOLVE IMPORTANT QUESTIONS ( ASSIGNMENT) OF GRAVITATION CLICK HERE-

     

     

     

     

     

     

  • Important questions of dual nature of radiation and matter

    Important questions of dual nature of radiation and matter

    Important questions of dual nature of radiation and matter

    Dual nature

    In this assignment, important questions of dual nature of radiation and matter , i am trying to provide some important questions based on the chapter dual nature of radiation and matter, student preparing for 12th board exam must solve all the questions , this chapter is little bit easier than other previous chapter of physics class 12th.Numerical based on this chapter is bit  easier than other chapters, so prepare this chapter nicely , and solve all the questions , i am sure that students will get benefit from this assignment of important questions of dual nature of radiation and matter.

    Dual nature of matter and radiation

    1. List important observations made by Lenard which lead to quantum theory of radiations .
    2. State De-Broglie hypothesis . Derive an expression for the De-Broglie wavelength associated with an electron accelerated through a potential V . draw the schematic diagram  of a localized-wave describe the wave nature of the moving electron .
    3. Define the term threshold frequency and stopping potential in relation to the phenomenon of photoelectric effect . how is photoelectric current affected on increasing the (I) frequency (II) intensity of the incident radiations and why?
    4. Sketch the graphs showing the variation of stopping potential with frequency of incident radiations for two photosensitive radiations for two photosensitive materials A and B having threshold frequencies ѵ0 > ѵ0’ respectively . (I) which of the two metals ,A and B has higher work function ? (II) what information do you get from the slope of the  graphs ? (III) what does the value of the intercept of graph  A on the potential axis represent ?                                                                                                                 FOR IMPORTANT QUESTIONS OF RAY OPTICS -CLICK HERE
    5. Draw the graphs showing the variation of photoelectric current with anode potential of a photocell for (I) the same frequencies  but different intensities I1 >I2 >  I3 incident radiation, (II) the same intensities but different frequencies  ѵ1> ѵ2 >ѵ3 of incident radiation . Explain  why the saturation current is independent of the anode potential.
    6. What is the photoelectric current ? Write Einstein’s photoelectric equation and use it to explain (I) independence of photoelectrons from intensity , of incident light , (II) Existence of threshold frequency for emission of photoelectrons.                                                                                                 FOR IMPORTANT QUESTIONS OF WAVE OPTICS AND OPTICAL INSTRUMENT CLICK HERE
    7. An electron of mass m  and charge q is accelerated from rest through a potential difference V  , obtain the expression for the de-Broglie  wavelength  associated with it . if electron and proton are moving with the same K.E. , which one of them will have a large De-Broglie wavelength associated with it ? give reason .
    8. State the dependence of the work function on the K.E. of electrons emitted in a photocell . (a) if the intensity of the incident radiation increases to double of its initial intensity what change occur in the (I) stopping potential and (II)photoelectric current.(b) if the frequency of the incident radiation is doubled what change occur in the (I) stopping potential (II)photoelectric current(III) K.E. of the photo electron emitted
    9. Given below in the graph between frequency of the incident light and maximum kinetic energy of the emitted photoelectron find the value of (I) threshold frequency and (II) work function from the graph.

      dual pic-1
    10. In a photoelectric effect experiment , the graph between the stopping potential V and frequency v of the incident radiation on two different metal plate P and Q  in the fig. (I) which of the two metal plates , P and Q has greater value of work function ?(II)what does the  slope of the lines depict ?

      dual pic-2
    11. Ultraviolet light of wavelength 2271 A from a 100W mercury source is incident on a photocell made of molybdenum metal , if the stopping potential is 1.3 V , estimate the work function of the metal.

    For latest cbse class-12th  physics sample paper click here-

    WHAT IS DIFFRACTION OF LIGHT ? TO KNOW COMPLETE ASSIGNMENT. CLICK HERE-

  • Important questions of atoms and nuclei

    Important questions of atoms and nuclei

    Important questions of atoms and nuclei.

    This topic is important for class 12th student . it is considered this chapter is little bit easier than other previous chapter of physics for board examination point of view . One important reason is that student already studied this chapter in class 11th (chemistry) , so it is easy to learn this chapter . Through “important questions of atoms and nuclei” ,  I am going to provide some important questions based on this topic . Student preparing for board examination of all board should revise all these questions given in ” important questions of atoms and nuclei”.

    Biot -savart's law
    ATOMS AND NUCLEI

    Here is some important questions of atoms and nuclei-

    Atoms- nuclei

    1. Draw a labelled diagram of alpha particle scattering experiment. Give Rutherford observations and discuss the significance of this experiment .
    2. Using postulates of Bohr energy of hydrogen atom ,show that (a) the radii of orbits increases as n2 and (b) the total energy of the electron increases as 1/n2 , where n is the principle quantum number of the atom .
    3. Draw a schematic arrangement of the Gieger -Marsden experiment for studying alpha particle scattering by a thin foil of gold . describe briefly , by drawing trajectories of the scattered alpha particle . haw this studies can be used to estimate the size of the nucleus ?

     

    1. State any two postulates of Bohr theory of hydrogen atom . what is the maximum possible no. of spectral lines observed when the hydrogen atom is in its second exited state ? justify your answer . calculate the ratio of the max. and min. wavelength of the radiation emitted in this process.

     

    1. Using Bohr postulates for hydrogen atom , show that the total energy of the electron in the stationary states can be expressed as the sum of kinetic energy(K) and potential energy (U) , where K=-2U. hence , deduce the expression for the total energy in the nth energy level of hydrogen atom   .

     

    1. The energy of an electron in the ground state of hydrogen atom is -13.6 Ev. (i) what does the negative sign signify ? (ii)how much energy is required to take an electron in this atom from the ground state to the first exited state?

     

     

    1. In Bohr theory of hydrogen atoms, calculate the energy of the photon emitted during a transition of the electron from first exited state to its ground state . write in which region of the electromagnetic spectrum this transition lies. Given R=1.03 * 107m-1.
    2. The electron in a given Bohr orbit has a total energy of -1.5Ev. calculate its(i) kinetic energy(ii)potential energy (iii) wavelength of the radiation emitted , when this electron makes a transition to the ground state.
    3. The energy level diagram of an element is given below . identify using necessary calculations , which transition corresponds to the emission of the spectral line of wavelength 102.7 nm . which transition corresponds to the emission of radiation of maximum wavelength?

    .

    atoms and nuclei

     

     

    1. The ground state energy of hydrogen atom is -13.6 eV.  ( I ) What is the potential energy of an electron in the third exited state? (ii) what will be the maximum and minimum wavelength of the emitted  radiation of Lyman series of hydrogen spectrum.

     

    1. State and explain the law of radioactive decay. Plot the graph of showing the number  (N)  of undecayed nuclei as a function of time (t) for a given radioactive sample having half life T1/2.depict in the plot the number of undecayed nuclei at (i) t=3T1/2­ (ii) t=5T1/2.

     

    1. How the size of nuclei is experimentally determined ? write the relation between the radius and mass number of the nucleus . show that the density of the nucleus is independent of its mass number. Two nuclei of mass number in the ratio 27:125. What is the ratio of their nuclear radius and , ratio of their densities.

     

    1. (i)Define the activity of the radioactive material and write its SI unit. plot a graph showing the variation of activity with respect to time of a given radioactive sample.(ii) what is meant by half life time of a radioactive element ? the half life of a radioactive sample is 30s calculate (a) the decay constant and (b)time taken for the sample to decay by 3/4thof the initial value .explain alpha , beta and , gama decay with an example . if an element 238X 92 converted into another element 222Y90 find the no of alpha and beta particles emitted.

     

    1. Draw the binding energy per nucleon curve . using the curve state clearly how the release in energy in the process of nuclear fission and nuclear fusion can be explained.

     

    1. Draw a plot of potential energy of a pair of nucleons , as a function of their separation . write two important conclusions which you can draw regarding the nature of nuclear force. Also, explain the mass of a nucleus , in the ground state is always less than total mass of its constituents neutron and proton .

     

    1. We are given the following atomic masses ; 238 U92 =238.05079u; 234 Th90=234.04363u ; 237Pa91=237.05121u; 1H1=1.00783u; 4He2=4.00260 u ;(a) calculate the energy released during alpha decay of uranium (b) calculate the kinetic energy of alpha particle ,and (c) show that ; 238 U92 cannot spontaneously emit a proton.

     

    1. The activity of a radioactive sample drop to 1/16 th of its initial value in 32 years . find the mean life of the sample .

     

     

  • test paper for class 11th

    test paper for class 11th

     test paper for class 11th

    this test paper specially design for the students of class 11th( physics) . this question paper covers questions from chapter 1st to chapter 6th . student can check there preparation using this test paper . this question paper also contain very important questions , so  students must try to solve these question  test paper for class 11th.

    projectile

                                                            Test -11th

    M.M.-30                                                                                                      TIME-1:00  

    All questions are compulsory , section- A contains 5 questions each carry 1 mark, section- B contains 7 questions each carry 2 marks ,section- C contains  12 questions each carry 3 marks , section-D  contains 3 questions each carry 5 marks.

      SECTION (A )                                                                                                                               

    1. The volume of an object as a function of time is calculated by where t is time in seconds and v is in cubic meter. Determine the dimensions of constants A and B.

     

    1. A stone is thrown such that its horizontal range is 4 times the maximum height. Find the angle of projection.

     

    1. A cricket ball of mass 150 g has an initial velocity m/s and final velocity  m/s after being hit. Calculate the change in momentum.
    2. What happens to coefficient of friction when the weight of a body is doubled ?
    3. If a man in an elevator drops his briefcase but it does not fall to the floor, what can you conclude about the elevator’s motion?

     

    SECTION-B

     

    1. When a particle rotates in a circle, a central force acts on it directed towards the center of rotation. Why does this force does no work on the particle?
    2. A cubical block rests on a plane of coefficient of friction √3. The angle through which the plane be inclined to the horizontal so that the block just slides down will be what? Also define angle of repose.
    3. Show that the path followed by the particle given angular projection is parabolic.
    4. If a projectile is projected with same initial velocity at two different angles α and β with the horizontal , if horizontal distance covered in both the cases are same thin find the ratio of there maximum height attained in both cases.
    1. The block of mass M moving on the frictionless horizontal surface collides with the spring of spring constant k and compress it by length L. Calculate the maximum momentum of the block after collision.               
    1. Explain impulse-momentum theorem. Give some practical applications of impulse.
    2. State and explain work energy principle using calculus method.

             SECTION-C

    1. The displacement of a body is proportional to t3, where t is time elapsed , then what will be the nature of velocity-time and acceleration – time graph. Also plot the position time graph for the uniform motion of an object along a straight line , if (i) x0=positive , v=negative and magnitude of velocity is constant (ii) both x0 and v are negative  and magnitude of velocity is constant.
    1. Explain Parallax method, how it is used to find the radius of the planet ?
    1. The escape velocity v of a body depends on the (i) acceleration due to gravity,(ii)the radius R of the planet. Establish dimensionally the relation for the escape velocity. Also write the dimension of gravitational constant G.
    1. Define acceleration due to gravity. Obtain relations to show how the value of ’g’ changes with (i) altitude , (ii) depth .

     15. state and derive Kepler’s laws of area and periods for circular orbits.

    1. A man can jump 1.5 m on earth . calculate the height he may be abled to jump on a planet whose density is one quarter that of earth and whose radius is one third that of earth.

     19.A uniform circular disc of radius R is rolling on a horizontal surface . Determine the tangential velocity (i) at the upper most point ,(ii)at the center of mass and (iii) at the point of contact. 

    1. A body is moving with uniform acceleration , its velocity after 5 sec is 25m/s and after 8 sec is 34m/s. calculate distance it cover in 15th sec .
    1. A pump on the ground floor of a building can pump up water to fill a tank of volume 30 m3 in 15 min. If the tank is 40 m above the ground , how much electric power is consumed  by the pump , the efficiency of the pump is 30%.

     22.Define spring constant , write the characteristics of the force during the elongation of the spring . Derive the relation for the potential energy stored when it is elongated by the distance X .

    1. (i) A light and heavy body have same kinetic energy , which of the two have more momentum and why? (ii) If kinetic energy of a body is increased by 300% , find the % increase in its momentum.
    1. Two blocks of mass 2kg and 5kg are connected by a light and inextensible string passing over a frictionless pulley . the block of mass 2 kg is free to slide on a surface inclined at an angle of 300 with the horizontal whereas 5 kg block hangs freely . find the acceleration and tension in the string.

     SECTION-D

    1. What do you mean by Banking of roads. What is the need of banking a circular road. Discuss the motion of car on banked circular road(with friction).

    A vehicle running with speed 72 km/hr applies brakes producing a retardation of 3 m/s2 while taking a turn of radius 100 m. Find the acceleration.

    1. State and prove the theorem of (i) parallel axis and , (ii) perpendicular axis . Also  find the moment of inertia of a circular disc about the axis perpendicular to the plane and passing through the center .
    1. How does a perfectly elastic collision is different from perfectly inelastic collision ? Two particles of mass m and M having velocities u1 and ­u­2 respectively make an head on collision .Derive the relation for their final velocities . discuss the following special cases (i)m=M (ii) m>M and  u2=0