# CBSE Delhi-Set-3-2008

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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

Name the absorbing material used to control the reaction rate of neutrons in a nuclear reactor.

Marks:1

Cadmium rods are the absorbing material used to control the reaction rate of neutrons in a nuclear reactor.

• Q3

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.

• Q4

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.

• Q5

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

Marks:1

• Q6

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.

• Q7

How does the power of a convex lens vary, if the incident red light is replaced by violet light?

Marks:1

The power increases because the refractive index of a material is more for violet colour.

• Q8

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

• Q9

Draw a ray diagram of a compound microscope. Write the expression for its magnifying power.

Marks:2

Ray diagram for the formation of image in a compound microscope

Magnifying power:- M = (L/f0) (1 + D/fe)
Where M = Magnifying power.

L   = Length of microscope tube (= v).

fo   = Focal length of objective lens.

D   = Least distance of distinct vision.

fe   = Focal length of eye piece.

• Q10

A ray of light passing through an equilateral triangular glass prism from air undergoes minimum deviation when angle of incidence is 3/4th of the angle of prism. Calculate the speed of light in the prism.

Marks:2

We have,
A= 600
i1= i2 = (3/4)A = 450  (according to given condition)
Determining the value of ,
A + = i1+i2.

or 600 = 450+450.

= 900 - 600 = 300.

The speed of light is given by,