 CBSE [All India]-Set-2-2011

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• Q1

Define electric dipole moment. Write its SI Unit.

Marks:1

Electric dipole moment is a vector quantity whose magnitude is equal to the product of the either magnitude of charges and distance between them. Its direction is from negative charge to positive charge. Its SI Unit is Coulomb-metre (Cm).

• Q2

Write any two characteristic properties of nuclear force.

Marks:1

Two characteristics of nuclear force are:

(i) It acts between two protons or two neutrons or between a proton and a neutron.

(ii) It is short range force and effective up to few femtometres.

• Q3

How are X-rays produced?

Marks:1

X-rays are produced by incidence of highly energetic electrons on a metal target in a special device called Coolidge tube.

• Q4

Where on the surface of Earth is the angle of dip zero?

Marks:1

The angle of dip is zero on the equator of earth.

• Q5

Two bar magnets are quickly moved towards a metallic loop connected across a capacitor ‘C’ as shown in the figure. Predict the polarity of capacitor. Marks:1

As per the given figure, upper side plate will be positive and lower side plate will be negative according to Lenz’s Law. • Q6

What happens to the width of depletion layer of a p-n junction when it is (i) forward biased, (ii) reverse biased?

Marks:1

When p-n junction is forward biased, its depletion layer decreases and in reverse bias, it increases.

• Q7

Define the term ‘stopping potential’ in relation to photoelectric effect.

Marks:1

For a particular frequency of incident radiation, stopping potential is the minimum negative or retarding potential given to the photoelectric plate for which the photocurrent stops or becomes zero.

• Q8

A hollow metal sphere of radius 10 cm is charged such that the potential on its surface is 5 V. What is the potential at the centre of the sphere?

Marks:1

Potential at the centre of sphere is 5 V. It is because inside the metallic hollow sphere, potential remains same as of surface.

• Q9

A thin straight infinitely long conducting wire having charge density λ is enclosed by a cylindrical surface of radius r and length l, its axis coinciding with the length of wire. Find the expression for the electric flux through the surface of cylinder.

Marks:2 In the given figure,

r = radius of cylindrical surface

l = length of cylindrical surface • Q10

Net capacitance of three identical capacitors in series is 2µF. What will be their net capacitance if connected in parallel?
Find the ratio of energy stored in the two configurations if they are both connected to the same source.

Marks:2

Let each capacitor has capacitance C. So, in series connection,

3C = 2µF

or, C = 2/3 µF

In parallel connection,

Cequivalent =C/3 = 2µF/9 = 2/9 µF

Energy stored, U = ½ CV2 So, Useries : Uparallel = 9:1