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CBSE Class 12 Physics Solved Question Paper 2015

Short Answer Type

1. Define capacitor reactance. Write its S.I. units.

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2. What is the electric flux through a cube of side 1 cm which encloses an electric dipole?

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Graph showing the variation of current versus voltage for a material GaAs is shown in the figure. Identify the region of

i) negative resistance

ii) where Ohm’s law is obeyed.

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4. Use Kirchhoff’s rules to obtain conditions for the balance condition in a Wheatstone bridge.

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Name the parts of the electromagnetic spectrum which is

(a) suitable for radar systems used in aircraft navigation.

(b) used to treat muscular strain.

Write in brief, how these waves can be produced.

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A cell of emf ‘E’ and internal resistance ‘r’ is connected across a variable load resistor R. Draw the plots of the terminal voltage V versus
(i) R and
(ii) the current I.

It is found that when R = 4 Ω , the current is 1 A and when R is increased to 9 Ω , the current reduces to 0.5 A. Find the values of the emf E and internal resistance r.

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7.
Two capacitors of unknown capacitances C₁ and C₂ are connected first in series and then in parallel across a battery of 100 V. If the energy stored in the two combinations is 0.045 J and 0.25 J respectively, determine the value of C₁ and C₂. Also, calculate the charge on each capacitor in parallel combination.

When the capacitors are connected in parallel,

Equivalent resistance,

Energy stored in capacitors, E_P =

When the capacitors are connected in series,

Putting this in equation (2), we get

C_{2 =}50 – 11.2 = 38.2 μF

The charge on capacitor is given by, Q = CV

Charge on capacitor 1, C₁ =

Charge on capacitor 2, C₂=

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State the principle of working of a galvanometer.

A galvanometer of resistance G is converted into a voltmeter to measure upto V volts by connecting a resistance R₁ in series with the coil. If a resistance R₂ is connected in series with it, then it can measure upto V/2 volts. Find the resistance, in terms of R₁ and R₂, required to be connected to convert it into a voltmeter that can read upto 2 V. Also find the resistance G of the galvanometer in terms of R₁ and R₂.

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An inductor L of inductance X_Lis connected in series with a bulb B and an ac source.

How would brightness of the bulb change when (i) number of turn in the inductor is reduced, (ii) an iron rod is inserted in the inductor and (iii) a capacitor of reactance X_C = X_L is inserted in series in the circuit. Justify your answer in each case.

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