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ISC Class 12 Physics Solved Question Paper 2009

Short Answer Type

21.

(i) What is meant by:

(1) Drift velocity and

(2) Relaxation time?

(ii) A metallic plug AB is carrying a current I (see Figure 4 below). State how the drift velocity of free electrons varies, if at all, from end A to end B.

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22. Figure below shows a uniform manganin wire XY of length 100 cm and resistance 9 Ω, connected to an accumulator D of emf 4 V and internal resistance 1 Ω through a variable resistance R. E is sa cell of emf 1.8 V connected to the wire XY via a jockey J and a central zero galvanometer G. It is found that the galvanometer shows no deflection when XJ = 80 cm. Find the value of R.

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23. Obtain an expression for magnetic flux density ‘B’ at the center of a circular coil of radius R and having N turns, when a current I is flowing through it.

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24.

(i) State any two differences between a moving coil galvanometer and a tangent galvanometer.

(ii) What is the use of a Cyclotron?

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25. What is meant by the time constant of an LR circuit? When the current flowing through a coil P decreases from 5A to 0 in 0.2 seconds, an emf of 60 V is induced across the terminals of an adjacent coil Q. Calculate the coefficient of mutual inductance of the two coils P and Q.

Time constant: Time constant for series RL circuit may be defined as the time in which the current rises from zero to 0.632 of its final steady value.

Here,

e_m = 60 V

dl = 5 - 0 = 5 A

and

dt = 0.25

We know,

open vertical bar straight e subscript straight m close vertical bar space equals space M space fraction numerator d I over denominator d t end fraction C o e f f i c i e n t space o f space m u t u a l space i n d u c t a n c e comma space M space i s comma space M space equals space open vertical bar e subscript m close vertical bar space x space fraction numerator d t over denominator d I end fraction space equals space 60 space x space fraction numerator 0.2 space over denominator 5 end fraction space equals space 2.4

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26.

When an alternating emf e = 300 Sin (100 πt + π/6) Volt is applied to a circuit, the current I through it is I = 5.0 Sin (100 πt - π/6) ampere. Find the :

(i) Phase difference between the emf and the current.

(ii) Average power consumed by the circuit.

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27. Obtain an expression for resonant frequency ‘f₀’of a series LCR circuit.

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28.

In which part of the electromagnetic spectrum, do the following radiations lie:

(i) Having wavelength of 20 nm

(ii) Having frequency of 10 MHz

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29. A thin convex lens which is made of glass (refractive index 1.5) has a focal length of 20 cm. It is now completely immersed in a transparent liquid having refractive index 1.75. Find the new focal length of the lens.

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