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# Very important numericals physics( term-2)

Important numericals physics term-2 (CBSE)

1. What is apparent position of the object below a rectangular block of glass 6cm thick , if a layer of water 4cm thick is on the top of the glass ? Refractive index of glass and water with respect to air is 3/2 and 4/3 respectively.
2. A screen is placed 100cm from an object  . The image of the object on the screen is formed by a convex lens at two different locations , separated by distance 20cm . calculate the focal length of the lens used.
3. You are given three lenses  L1 , L2,L3 each of focal length 10cm . an object is kept at 15cm in front of L1  ,  as shown in fig. the final image is formed at the focus of L3 find the separation between the lenses.
• 4. A convex lens made up of glass of refractive index 1.5 is  dipped  , in turn ,in (a) a medium of refractive index 1.65 (b)   ) a medium of refractive index 1.33.Will it behave like converging or diverging lens in two cases, explain how focal length changes in two cases .
• 5.Three rays  red  , green and blue are incident on a right angled prism ABC at face AB the refractive indices of the material  of the prism for red, green ,and blue are 1.39,1.44, and 1.47 respectively . Out of the three which colour of ray emerge out of face AC. Trace the path of the three rays after passing through AB.
• 6. State the conditions under which total internal reflection occurs . one face of a prism with a refracting angle of 30 , is coated with silver . A ray incident on  another face at an angle of 45 is refracted and reflected from the silver coated face and retrace its path. Find the refractive index of the material of the prism.
• 7. Find the position of the image formed by the lens combination given in figure
• 8. A diverging lens of focal length f cut into two identical parts ,each forming a plano- convex lens what is the focal length of each part. How the focal length of the lens changes if it bisected axially?
• 9. The image of a needle placed 45cm from a lens is formed on a screen placed 90 cm on the other side of lens. Find displacement of image if object is moved 5cm away from lens.
• 10. A small bulb is placed at  the bottom of a tank containing water to a depth of 80 cm . what is the area of the surface of water through which light of the bulb can emerge out ?Refractive index of water is 1.33 consider the bulb to be a point source.
•  11. Yellow light of wavelength λ= 6000 A illuminate a single slit of width 1 x 10-4 m calculate (i) the distance between two dark lines on either side of the central maximum when the diffraction pattern is on screen kept 1.5 m away from the slits , (ii) the angular spread of the first diffraction minima .

Ans- 1.8 cm , 6x 10-3 rad . 12. Two wavelength of sodium light 590 nm are used in turn , to study the diffraction taking place at the single slit of aperture  2x 10-4 m . The distance between the slits and the screen is 1.5 m . Calculate the separation between the position of first maxima of the diffraction pattern obtained in the two cases .

Ans-6.75×10-5m . 13. (a) In a single slit diffraction , a slit of width d is illuminated by red light of wavelength 650 nm . For what value of  d will (i) the first minimum fall at an angle of diffraction of 300 , and   (ii) the first maximum fall at an angle of diffraction of 300

(b) Why does the intensity of secondary maximum becomes less as compared to the central maximum .

Ans- 1.3 x10-6 m , 1.95×10 ‑6‑ m 14. A monochromatic light of wavelength 500 nm is incident normally on a single slit of width 0.2 mm to produce a diffraction pattern . Find the angular width of the central maximum obtained on the screen . Also estimate the number of fringes obtained in YDSE with fringe width 0.5 mm , which can be accommodate within the region of total angular spread of the central maximum due to single slit .            Ans- ϴ=0 to 2.5×10-3 ; n=D/2 ;D+1 15.A beam of light consisting of two wavelength 800nm and 600 nm is used to obtain the interference pattern in YDSE on a screen placed 1.4 m away . If the two slits are separated by 0.28mm , calculate the least distance from the central bright maximum where the bright fringes of the two wavelengths coincide . Ans- n=3 ; 1.2 cm . 16. In YDSE using monochromatic light of wavelength λ, the intensity of light at a point on the screen where path difference is λ is K units . Find out the intensity of light of light at a point where path- difference is λ/3 . 17. The ratio of the intensity at minima to the maxima in YDSE is 9:25 , find the ratio of the width of the two slits , also find the ratio of amplitude .   Ans- 16:1 . 18. Two wavelength of sodium light of 590 nm and 596 nm are used in turn to study the diffraction taking place at a single slit of aperture 2×10-6 m . The distance between the slit and the screen is 1.5 m . Calculate separation between the position of first maxima and of the diffraction pattern obtained in the two cases .

Ans- 6.75 nm .

19. 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.

20. 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?

21. 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.

22. 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? .

23.The first line of Lyman series in hydrogen spectrum has a wavelength of 1220 Å. Calculate the wavelength of the second member of the series.

24. A nucleus at rest splits up into two parts with velocity ratio 2 : 1 calculate the ratio of their radii of the ratio the two nuclear fragments.

25.The ground state energy of electron in hydrogen atom is – 13.6 eV. Find the kinetic energy and potential energy of the electron in (i) ground state (ii) first excited state.