# CBSE [All India]-Set-3-2012

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• Q1

Two wires of equal length, one of copper and the other of manganin have the same resistance. Which wire is thicker?

Marks:1

We know that,

Thus, manganin is thicker.

• Q2

A bar magnet is moved in the direction indicated by the arrow between two coils PQ and CD. Predict the directions of induced current in each coil.

Marks:1

The direction of induced current will be clockwise in both the coils. In first coil, the direction of induced current is from P to Q and in the second coil the direction is from C to D.

• Q3

For the same value of angle of incidence, the angles of refraction in three media A, B  and C are 15°, 25° and 35° respectively. In which medium would the velocity of light be minimum?

Marks:1

Therefore, velocity of light is minimum in medium ‘A’.

• Q4

A proton and an electron have same kinetic energy. Which one has a greater de-Broglie wavelength and why?

Marks:1

• Q5

Mention the two characteristic properties of the material suitable for making core of transformer?

Marks:1

Two characteristic properties of the material suitable for making core of transformer are:
(i) It should have low coercivity and low retentivity.
(ii) It should have a smaller hysteresis loop.

• Q6

A charge ‘q’ is placed at the centre of a cube of side l. What is the electric flux passing through each face of the cube?

Marks:1

• Q7

How does the fringe width, in Young’s double-slit experiment, change when the distance of separation between the slits and screen is doubled?

Marks:1

On doubling the distance of separation between the slits and screen, the fringe width becomes twice.

• Q8

The speed of an electromagnetic wave in a material medium is given by   being the permeability of the medium and  its permittivity. How does its frequency change?

Marks:1

• Q9

An electric dipole is held in a uniform electric field.
(i) Show that the net force acting on it is zero.
(ii) The dipole is aligned parallel to the field. Find the work done in rotating it through an angle of 180°.

Marks:2

(i)

(ii)
W = change in potential energy
= Ufinal – Uinitial
= (–pE cos180°) – (–pE cos0°)
= 2pE