Potentiometer – An instrument used to measure accurately the EMF or potential difference is called potentiometer.
Principle– Its working based on the principle that the potential drop across a conductor is directly proportional to the length of the conductor , if constant current passes through the conductor having uniform area of cross-section .
Construction –
POTENTIOMETER
As we know ,
potential V=IR
V = (ρl/A) I
Since current is constant and area of cross-section is uniform so V α l
Or V = K l
K = V/l ( K is a constant called potential gradient)
[ calculation of potential gradient ( students don’t have to derive it in case of potentiometer it is useful for the numerical questions) – if Rh = r and resistance of the wire is r and E is the emf of driver cell then , current through the circuit is , i = E/ (R+r)
There fore potential difference at the end the wire is v= i r
V= {E/ (R+r) } r . so potential gradient K = V/l = {E/ (R+r) } r/l. ]
Potantiometer is preferred over the galvenometer to measure potential difference across a conductor
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THIS ASSIGNMENT PROVIDE ALL IMPORTANT QUESTIONS OF CURRENT ELECTRICITY CHAPTER .
This question paper is designed for quick revision for the students of class 12th appearing in the class test or board examination , if students have to practice the question of current electricity in broad level click on complete assignment of electric current
1 (i)State the working principle of a potentiometer. With the help of the circuit diagram, explain how a potentiometer is used to compare the emf’s of two primary cells. Obtain the required expression used for comparing the emf’s.
(ii) write two possible causes for one sided deflection in a potentiometer experiment.
(iii)Which material is used for potentiometer wire and why?
(iv)how can the sensitivity of a potentiometer be increased?
2. Answer the following
(i) Why are the connections between the resistor in a meter bridge made of thick copper strips?
(ii)Why is it generally preferred to obtain the balance point in the middle of the meter bridge wire?
(iii)which material is used for the meter bridge wire and why?
3. (i)State with the help of a circuit diagram, the working principle of a meter bridge. Obtain the expression used for determining the unknown resistance.
(ii) what happens if the galvanometer and cell are interchanged at the balance point of the bridge?
(iii) why is it considered important to obtain the balance point near the mid- point of the wire?
4. (a) A cell of emf E and internal resistance r is connected across a variable resistor R. Plot a graph showing the variation of terminal potential V with resistance R.
(b) Plot a graph showing the variation of terminal potential difference across a cell of emf E and internal resistance r with current drawn from it. Using this graph how does one determine the emf of the cell?
5. Two conducting wires X and Y of same diameter but different materials are joined in series across a battery. If the number of density of electrons in X is twice than that in Y, then find the ratio of drift velocity of electrons in the two wires.
THIS QUESTION PAPER CONTAINS THE IMPORTANT QUESTIONS OF ELECTROSTATIC POTENTIAL AND CAPACITANCE IT IS IMPORTANT FOR THE BOARD EXAMINATION FOR CLASS 12TH
What do you mean by the term equipotential surface ? Draw the equipotential surface for (i) a point charge, (ii) an electric dipole , (iii) two positive charges of equal magnitude separated by some distance (iv) two uniformly large parallel thin plates having charge density +σ and -σ separated d distance apart. Can two equipotential surface intersect each other ? give reason. Why there is no work done in moving a charge fro one point to other on an equipotential surface? TO DOWNLOAD COMPLETE QUESTIONS PAPER CLICK HERE –ELECTROSTATIC POTENTIAL AND CAPACITANCE
This assignment contains very important questions of ELECTRIC CHARGES AND FIELDS
Explain the following terms –(a) Quantisation of charge . (b) Additivity of charge and (c) conservation of charge.
What is electric field lines ? Draw the field lines for (a) A positive charge (b) A negative charge (c) An electric dipole (d) Two positive charge having equal magnitude separated by some distance, (e) ) Two positive charge having different magnitude separated by some distance, and (f) A plane positively charged sheet (g) A positive point charge (+q) is kept in the vicinity of an uncharged conduction plate. Sketch the electric field lines originated from the point on to the surface of the plate. Also explain why ( I ) Field lines never intersect each other? (ii) Why field lines always comes out normally to the surface ?
What do you mean by the term electric dipole and dipole moment? Is it scaler or vector quantity? Find the electric at a point the (i) axial and (ii) equatorial point , also find the relation between them . Also deduce an expression for the torque acting on a dipole and energy stored in the dipole when it is placed in the uniform electric field E .What will happen to the dipole when it is placed in non – uniform electric field?
State and prove Gauss theorem . Using Gauss’s theorem find the magnetic field at a point due to (i) straight charged wire , (ii) plane charged sheet , show that it is independent of distance of the point from the sheet , and (iii) charged spherical shell also plot the graph between electric field and separation of point from the centre of the shell. Using Gauss’s law also derive an expression for the electric field between two uniformly charged parallel sheets of charge density σ and -σ respectively
(i)Define electric flux , write its SI unit . (ii)The electric field components due to a charge inside the cube of side 0.1m are shown below Ex=αx , where α =500N/C-m EY=0,EZ=0Calculate (a) The flux through the cube (b)the charge inside the cube CLICK HERE TO DOWNLOAD-Very important questions for ELECTRIC CHARGES AND FIELD
OBJECTIVE TYPE QUESTIONS OF ELECTROSTATICS FOR THE STUDENTS PREPARING FOR JEE/ NEET/AIIMS.
OBJECTIVE TYPE QUESTIONS OF ELECTROSTATICS questions will help the students to practice the entire chapter of ELECTROSTATICS …..Having solved these question students will be able to solve all questions in all competitive examinations based on this chapter . Section A is for NEET and XII(board), section B is for JEE students.
Here is another set of important objective questions for class 12th which contain all important questions of electric field and potential only, it will help the students to practice this chapter well , for board examination point of view .
THIS VIDEO HOW TO SELECT COACHING CENTER FOR JEE AND NEET/AIIMS PREPRATION WILL HELP THE STUDENTS THAT WHICH COACHING CENTER SHOULD HE JOIN OR SHOULDN’T HE JOIN . WHAT KIND OF STUDENTS SHOULD JOIN SUCH KIND OF CLASSROOM….
Laws of motion assignment deals with the questions based on the topic , Inertia, newton’s first ,second and third laws,momentum ,impulse,linear momentum all kind of friction , and circular motion.
In this topic we will, discuss about working of cyclotron , its principle, construction and its limitations. (** this topic is removed from the syllabus of class 12th, board examination).To know the complete syllabus click on the given link-
It is a device used to accelerate positive charged particles like proton, deutron , alpha particles etc . with desired velocity.
Principle– Its working based on the principle that a positive charge particle can be accelerated to a sufficient high energy with the help of oscillating electric field with the help of perpendicular strong magnetic field .
Construction– It consist two D-shaped chamber ( Dees) D1 and D2 , which are placed slightly separated with each other between two poles of the magnet N- pole and S–pole ( as shown in figure. ) Dees are connected with an high frequency oscillator ( cause of variable electric field).
Working and theory– suppose initially the D1 is negative and D2 is positively charged , then the positive charged particle at point P starts to move towards D1 , but due to perpendicular magnetic field it starts moving on a circular path. If r is the radius of the circular path then ,
mv2/r = qvB
So r = mv/qB ;
Time taken by the charged particle to complete half cycle t= ∏r/v = ∏m/qB ;
When particle reaches to D1 at the same time D1 becomes positively charge and D2 negatively then again charge particle starts to move towards D2 with the circular path with greater radius . similarly charge particle remain describing the circular path with greater radius and greater speed and at an instant it ejected through the window with high kinetic energy .
Maximum energy of charged particle– suppose v0 , r0 is the is the maximum velocity and maximum radius of the circular path followed by the charged particle ,
Then ,m v02/ r0 = B q v0 or , v0 = Bq r0/m ,
Therefore maximum kinetic energy k = ½ mv02 = B2 q2 r02 / 2m ;
Cyclotron frequency –
Angular velocity ω= Bqr/mr = Bq/m ……………..(3)
here frequency f=ω/2∏ = Bq/2∏m ( here frequency is independent of velocity)………….(4)
limitations of cyclotron-
When a positive ion is accelerated by the cyclotron , it moves with greater speed when it becomes closer to speed of light or comparable with speed of light , then mass of the particle increases according to the given relation m= m0 /√(1-v2/c2) where m0 is the mass of the charged particle , v is the speed of charged particle , c is the speed of light . But cyclotron doesn’t discuss about variable masses .
Cyclotron is suitable for accelerating heavy particles only . i.e electron can not be accelerated through cyclotron .
The uncharged particle can not be accelerated by the cyclotron.
To watch the video on motion of a charged particle in magnetic field click here-
CURRENT ELECTRICITY
