 # CBSE Delhi-Set-2-2008

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• Q1

What is the direction of the force acting on a charged particle q, moving with a velocity in a uniform magnetic field ?

Marks:1

The force is given by This force is right angles to & .

• Q2

State the reason, why two independent sources of light cannot be considered as coherent sources.

Marks:1

Because, they will produce the phase difference and produce interference.

• Q3

Name the part of the electromagnetic spectrum of wavelength 10-2m and mention its one application.

Marks:1

Microwaves. It is used in radar & communication purposes.

• Q4

A 500 charge is at the center of a square of side 10 cm. Find the work done in moving a charge of 10 C between two diagonally opposite points on the square.

Marks:1

According to the given condition, we have

VOA = VOB

Therefore,  work done is given by

W = q( VOB - VOA)

Hence, W is zero.

• Q5

The plot of the variation of potential difference across a combination of three identical cells in series, versus current is as shown below. What is the emf of each cell? Marks:1

Since all the cells are connected in series so current flowing through each cell is same. Therefore total resistance given by
Rt = 6/1 = 6 Internal resistance of each cell is 6/3 = 2 Now e.m.f. of each cell is  = 2 x 1A = 2 volts

• Q6

An electron and alpha particle have the same de-Broglie wavelength associated with them. How are their kinetic energies related to each other?

Marks:1 • Q7

A converging lens of refractive index 1.5 is kept in a liquid medium having same refractive index. What would the focal length of the lens in this medium?

Marks:1 • Q8

How does the angular separation of interference fringes change, in Young’s experiment, if the distance between the slits is increased?

Marks:1

When the separation between slits is increased, d increases. Therefore fringe width β decreases.

• Q9

Distinguish between an intrinsic semiconductor and p-type semiconductor. Give reason, why, a p-type semiconductor is electrically neutral, although nh>>ne ?

Marks:2

An intrinsic semiconductor is a pure semiconductor where as a p-type semiconductor is a semiconductor doped with trivalent impurity atoms like boron or gallium. An intrinsic semiconductor has same number of holes and electrons while in a p-type semiconductor the number of holes is greater than the number of electrons. Each hole is associated with a nearby negative-charged dopant ion, and thus semiconductor remains electrically neutral as a whole .

• Q10

Define magnetic susceptibility of a material. Name two elements, one having positive susceptibility and the other having negative susceptibility. What does negative susceptibility signify?

Marks:2