CBSE Outside Delhi_Ajmer-Set-3 (2015)
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Q1
When light travels from an optically denser medium to a rarer medium, why does the critical angle of incidence depend on the colour of light?
Marks:1View AnswerAnswer:
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Q2
Define dielectric constant of a medium. What is its S.I. unit?
Marks:1View AnswerAnswer:
Dielectric constant of a medium is the ratio of absolute electrical permittivity of the medium to the absolute electrical permittivity of free space.
It has no units. -
Q3
What is the function of a band pass filter used in a modulator for obtaining AM signal?
Marks:1View AnswerAnswer:
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Q4
A planar loop of rectangular shape is moved within the region of a uniform magnetic field acting perpendicular to its plane. What is the direction and magnitude of the current induced in it?
Marks:1View AnswerAnswer:
As the magnetic field linked with the loop is not changing with time, therefore, there is no current induced in the loop.
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Q5
V–I graph for a metallic wire at two different temperatures T1 and T2 is as shown in the figure. Which of the two temperatures is higher and why?
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Q6
Determine the distance of closest approach when an alpha article of kinetic energy 4·5 MeV strikes a nucleus of Z=80, stops and reverses its direction.
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Q7
Differentiate between amplitude modulated (AM) and frequency modulated (FM) waves by drawing suitable diagrams. Why is FM signal preferred over AM signal?
Marks:2View AnswerAnswer:
In amplitude modulation, the amplitude of the carrier signal is varied in accordance with the instantaneous amplitude of the information signal.
In frequency modulation, the frequency of the carrier signal is varied in accordance with the instantaneous frequency of the information signal.
FM signal is preferred over AM signal due to the following reasons:(i) FM transmission is efficient compared to AM transmission. This is because the transmitted power is constant due to the constant amplitude of FM wave irrespective of modulation index.
(ii) FM reception is almost immune to noise as compared to AM reception. This is because noise is a form of amplitude variation in transmitted signal. So it can be eliminated by using amplitude limiters in the FM receivers.
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Q8
When the electron orbiting in hydrogen atom in its ground state moves to the third excited state, show how the de Broglie wave length associated with it would be affected.
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Q9
Define a wavefront. Using Huygens’ principle, draw the shape of a refracted wavefront, when a plane wave is incident on a convex lens.
Marks:2View AnswerAnswer:
Wavefront is the locus of all the particles of a medium, which are vibrating in the same phase.
When a plane wavefront AB is incident on a convex lens, it is the central part of the incident wavefront AB that travels through the maximum thickness of the convex lens. This results in its delay and the emerging wavefront has a depression in the central portion. This gives a spherical wavefront which converges to a point F which is known as the focus.
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Q10
(a) When a wave is propagating from a rarer to a denser medium, which characteristic of the wave does not change and why?
(b) What is the ratio of the velocity of the wave in the two media of refractive indices
Marks:2View AnswerAnswer:
(i) When a wave is propagating from a rarer to a denser medium, its frequency doesn’t change.
(ii)
