# CBSE Delhi-Set-3-2009

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• Q1

Differentiate between a ray and a wave front.

Marks:1

Wave front is defined as the locus of all particles oscillating in the same phase during propagation of waves in a material medium. While a straight line drawn perpendicular to wave front gives the direction of propagation of wave and is known as a ray.

• Q2

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.

• Q3

At what angle of incidence should a light beam strike a glass slab of refractive index (3)1/2 . Such that the reflected and the refracted rays are perpendicular to each other?

Marks:1

r + 900 + c0 = 1800 (linear pair)

c0 = 900 – r….(i)

i + r = 900

i = 900 – r

Sin i= Sin (900 – r)

Sin i = Cos r….. (2)  (As sin(900- ) =  cos

• Q4

What is space wave propagation?

Marks:1

When the radio waves from the transmitting antenna reach the receiving antenna either directly, or after reflection from the earth’s surface (or in troposphere) then, the wave propagation is known as ‘space wave propagation’.

• Q5

Name the part of electromagnetic spectrum which is suitable for
(ii)         treatment of cancer tumours

Marks:1

(i) Microwaves.
(ii) X-rays.

• Q6

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.

• Q7

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.

• Q8

Two nuclei have mass numbers in the ratio 2 : 5. 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

• Q9

(i) Sketch the output waveform from an AND gate for the inputs A and B shown in the figure.

(ii)If the output of the above AND gate is fed to a NOT gate, name the gate of the combination so formed.

Marks:2

(i).

(ii). AND +  NOT = NAND

• 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