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CBSE Class 12 Physics Solved Question Paper 2016

Short Answer Type

11. Two long, straight, parallel conductors carry steady currents, I₁ and I₂ , separated by a distance . If the currents are flowing in the same direction, show how the magnetic field set up in one produces an attractive force on the other? Obtain the expression for this force. Hence, define one ampere.

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12. How are em waves produced by oscillating charges?

Draw a sketch of linearly polarised em waves propagating in the Z-direction. Indicate the directions of the oscillating electric and magnetic fields.

OR

Write Maxwell's generalisation of Ampere's circuital law. Show that in the process of charging a capacitor, the current produced within the plates of the capacitor is I =

straight epsilon subscript straight o space dϕ subscript straight E over dt

, where

straight ϕ subscript straight E

is the electric flux produced during charging of the capacitor plates.

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13.

Explain the terms (i) Attenuation and (ii) Demodulation used in Communication System.

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14. Plot a graph showing variation of de Broglie wavelength λ versus

fraction numerator 1 over denominator square root of straight V end fraction

, where V is the is accelerating potential for two particles A and B, carrying the same charge but different masses m₁ and m₂ (m₁ > m₂). Which one of the two represents a particle of smaller mass and why?

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15. A nucleus with mass number A = 240 and BE/A = 7.6 MeV breaks into two fragments, each of A = 120 with BE/A = 8.5 MeV. Calculate the released energy.

OR

Calculate the energy in the fusion reaction:

straight H presubscript 1 presuperscript 2 space plus space straight H presubscript 1 presuperscript 2 space rightwards arrow He presubscript 2 presuperscript 3 space plus space straight n space comma where space straight B. straight E. space of space straight H presubscript 1 presuperscript 2 space equals space 2.23 space MeV space space space space space space space space space space space space straight B. straight E. space of space He presubscript 2 presuperscript 3 space equals space 7.73 space MeV

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16. State Brewster's law.
The value of Brewster's angle for a transparent medium is different for light of different colours. Give reason.

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17. Write three characteristic features in photoelectric effect that cannot be explained on the basis of wave theory of light, but can be explained only using Einstein's equation.

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18.

(a) Explain any two factors that justify the need of modulating a low-frequency signal.

(b) Write two advantages of frequency modulation over amplitude modulation.

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19. (i) Write the functions of three segments of a transistor.

(ii) Draw a circuit diagram for studying the input and output characteristics of a n-p-n transistor in common emitter configuration. Using the circuit, explain how input, output characteristics are obtained.

i) The function of three segments of a transistor are:

Emitter: Emits the majority charge carriers

Collector: Collects the majority charge carriers

Base: Base provides the interaction between the collector and the base

ii) An n-p-n transistor is as shown below:

Input characteristics: The variation between the base current and the base-emitter voltage is obtained. Input characteristics is used to find input dynamic resistance of the transistor as it is represented by the slope.

Output characteristics: A graph representing the variation of the collector current and emitter voltage is obtained, keeping base current fixed. The slope fo the output characteristic graph gives us the output dynamic resistance.

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20. (a) Calculate the distance of an object of height h from a concave mirror of radius of curvature 20 cm, so as to obtain a real image of magnification 2. Find the location of image also.

(b) Using mirror formula, explain why does a convex mirror always produce a virtual image.

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