 CBSE Outside Delhi_Ajmer-Set-1 (2015)

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• Q1

Define dielectric constant of a medium. What is its S.I. unit?

Marks:1

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.

• Q2

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?

Marks:1

• Q3

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:1

As the magnetic field linked with the loop is not changing with time, therefore, there is no current induced in the loop.

• Q4

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:1

• Q5

What is the function of a band pass filter used in a modulator for obtaining AM signal?

Marks:1

• Q6

A variable resistor R is connected across a cell of emf ε and internal resistance r as shown in the figure. Draw a plot showing the variation of

(i)  terminal voltage V and (ii) the current I, as a function of R

Marks:2

(i) Terminal voltage across a cell is given by

As resistance, R increases, current in the circuit decreases and so, the terminal voltage increases.

(ii) The current across a circuit is given as

The current decreases with increase in R.

• Q7

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.

Marks:2

• Q8

Define a wavefront. Using Huygens’ principle, draw the shape of a refracted wavefront, when a plane wave is incident on a convex lens.

Marks:2

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.

• Q9

(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:2

(i) When a wave is propagating from a rarer to a denser medium, its frequency doesn’t change.

(ii)

• Q10

Differentiate between amplitude modulated (AM) and frequency modulated (FM) waves by drawing suitable diagrams. Why is FM signal preferred over AM signal?

Marks:2