# CBSE Delhi-Set-2-2009

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• Q1

The figure shows a plot of three curves a, b, c showing the variation of photocurrent vs collector plate potential for three different intensities I1, I2 and I3  having frequencies   respectively incident on a photosensitive surface.

Point out the two curves for which the incident radiations have same frequency but different intensities.

Marks:1

Curve a, b represents same frequency. The value of stopping potential is same for radiations having same frequency and is independent of the intensity of the incident radiation. Thus, a and b are the two curves for which the incident radiations have same frequency but different intensities.

• Q2

Draw a diagram to show refraction of a plane wave front incident in a convex lens and hence draw the refracted wave front.

Marks:1

Light travels slower in lens than in air. Thus, refracted wave front is converging spherical wave front A`P2B`.

• Q3

Name the electromagnetic radiation to which waves of wavelength in the range of 10-2 m belong. Give one use of this part of EM spectrum.

Marks:1

The electromagnetic radiation to which the waves of wavelength in the range of  10-2 belongs is Microwaves.
These waves are widely used in Radar.

• Q4

What is ground wave propagation?

Marks:1

When the radio waves emitted from the transmitting antenna propagate along the surface of the earth so as to reach the receiving antenna, the wave propagation is known as ground wave propagation.

• Q5

Two nuclei have mass numbers in the ratio 1 : 3. What is the ratio of their nuclear densities?

Marks:1

Density of nuclear matter= mass of nucleus / volume of nucleus

=(3m)/(4R03)

As m and R0 are constants, therefore density  is independent of the mass number of atoms of all elements.

So, nuclear density is same for all nuclei, therefore,

1/2 =1

• Q6

Unpolarized light is incident on a plane surface of glass of refractive index  at angle i. If the reflected light gets totally polarized, write the relation between the angle i and refractive index .

Marks:1

When the reflected light gets totally polarized after passing through the glass then, the relation between the angle  of incidence(i) and the refractive index () is given by

= tan iP     ( Brewster’s Law)
Where,

ip = polarizing angle.

• Q7

You are given following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct an astronomical telescope?

## Lenses

Power (P)

Aperture (A)

L1

3D

8 cm

L2

6D

1 cm

L3

10D

1 cm

Marks:1

Focal length of eyepiece should be smaller than that of objective.
So, power of eyepiece should be greater as compared to an objective.

 L1 3 D 8 cm Objective L3 10D 1 cm Eye piece

We will use L1 lens as an objective and L3 lens as an eyepiece to construct the astronomical telescope.

• Q8

Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid. Why?

Marks:1

Magnetic field lines can be entirely confined within the core of toroid because field lines form closed loops, but in case of straight solenoid it is not possible as it will violate Ampere’s law.

• Q9

A radioactive nucleus ‘A’ undergoes a series of decays according to the following scheme:

The mass number and atomic number of A4are 172 and 69 respectively. What are these numbers for A?

Marks:2

• Q10

By what percentage will the transmission range of a TV tower be affected when the height of the tower is increased by 21%?

Marks:2