Tuesday, 16 September 2014

Important question of electricity Class 12


Q.1 Define drift velocity and derive an expression for it and prove that I = neAVd
Q.2 State Kirchhoff’s laws and apply it to derive Wheatstone’s bridge principle.
Q.3 Draw V - I graph for ohmic and non-ohmic materials. Give one example for each.
Q.4 Define the term 'resistivity' and write its S. I. Unit. Derive the expression for the
resistivity of a conductor in terms of number density of free electrons and relaxation time.
Q.5 State the principle of potentiometer. Draw a circuit diagram used to compare the e.m.f. of two primary cells. Write the formula used. How can the sensitivity of a potentiometer be increased?
Q.6 Two cells of emf 1.5 V and 2 V and internal resistance 1 ohm and 2 ohm respectively are connected in parallel to pass a current in the same direction through an external resistance of 5 ohm. (i) Draw the circuit diagram. (ii) Using Kirchhoff's laws, calculate the current through each branch of the circuit and potential difference across the 5 ohm resistor.
Q.7 A cylindrical metallic wire is stretched to increase its length by 5%. Calculate the percentage change in its resistance.
Q.8
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Q.9 (a) Define emf. of a cell? On what factors does it depend?
(b) Figure below shows a 2.0v potentiometer used for the determination of internal resistance of a 1.5v cell. The balance point of the cell in open circuit is 76.3cm. When a resistance of 9.5 ohm is used in external circuit of the cell the balance point shifts to 64.8cm length of the potentiometer. Determine the internal resistance of the cell                                                    

. Q.10    
Physics Classes By Er.Shyam Pachori add: C.L 81 D.D Nagar               Mob.: 9039803981 Batches MWF Time: 3:30 - 5 pm        

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