A slab of material of dielectric constant K has the same area as

Subject

Physics

Class

CBSE Class 12

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

1.

Two charges of magnitudes – 2Q and + Q are located at points (a, 0) and (4a, 0) respectively. What is the electric flux due to these charges through a sphere of radius ‘3a’ with its centre at the origin?        

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2.

How does the mutual inductance of a pair of coils change when,

(i) distance between the coils is increased and

(ii) number of turns in the coils is increased?

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3.

Two identical cells, each of emf E, having negligible internal resistance, are connected in parallel with each other across an external resistance R. What is the current through this resistance?

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4.

The motion of copper plate is damped when it is allowed to oscillate between the two poles of a magnet. What is the cause of this damping? 

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5.

Welders wear special goggles or face masks with glass windows to protect their eyes from electromagnetic radiations. Name the radiations and write the range of their frequency. 

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6.

A slab of material of dielectric constant K has the same area as that of the plates of a parallel plate capacitor but has the thickness d/2, where d is the separation between the plates. Find out the expression for its capacitance when the slab is inserted between the plates of the capacitor. 


Capacitance having a dielectric of thickness ‘t’ is given by, 

                                 

When the thickness of the plates is reduced to half, t = d/2 then,

 Capacitance becomes, 

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7.

A capacitor, made of two parallel plates each of plate area A and separation d, is being charged by an external ac source. Show that the displacement current inside the capacitor is the same as the current charging the capacitor.  

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8.

Explain the term ‘drift velocity’ of electrons in a conductor. Hence obtain the expression for the current through a conductor in terms of ‘drift velocity’.

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9.

Describe briefly, with the help of a circuit diagram, how a potentiometer is used to determine the internal resistance of a cell.

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10.

(a) For a given a.c.,

(b) A light bulb is rated at 100 W for a 220 V a.c. supply. Calculate the resistance of the bulb. 

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