 # Physics: 2017: CBSE: [All India]: Set – II

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• Q1

A bar magnet is moved in the direction indicated by the arrow between two coils PQ and CD. Predict the direction of the induced current in each coil.

Marks:1

According to the Lenz’s law, the polarity of the induced emf is such that it opposes the change in magnetic flux responsible for its production.

As North pole of bar magnet is moving away from the coil PQ so the right end of the coil will develop South Pole i.e, induced current as seen from the left end will be anticlockwise.

As south pole of bar magnet is moving towards the coil CD so the left end of the coil will develop North Pole i.e, induced current as seen from the left end will be clockwise.

• Q2

Write the relation for the speed of the electromagnetic waves in terms of the amplitudes of electric and magnetic fields.

Marks:1

The speed of the electromagnetic waves is determined by the ratio of peak value of electric and magnetic fields:

• Q3

Nichrome and copper wires of same length and same radius are connected in series. Current I is passed through them. Which wire gets heated up more? Justify your answer.

Marks:1

Nichrome wire has higher value of resistivity as compared to copper wire. So nichrome wire will get heated up more as heat developed on passing current through a wire.

We know that:

Heat developed,H=I2Rt.

where, I is the current flowing through the wire,

R is the resistance of the wire and

T is the time duration for which current flows

through the wire.

Greater the value of resistivity, greater is resistance R.

• Q4

How does the angle of deviation of a glass prism vary, if the incident violet is replaced by red light? Give reason.

Marks:1

Angle of minimum deviation is directly proportional to the refractive index. Refractive index of red light is less than the refractive index of violet light in glass prism. Thus, angle of minimum deviation will decrease if the incident violet light is replaced by red light.

• Q5

Name the phenomenon which shows the quantum nature of electromagnetic radiation.

Marks:1

The phenomenon of Photoelectric effect shows the quantum nature of electromagnetic radiation.

• Q6

Find the condition under which the charged particles moving with different speeds in the presence of electric and magnetic field vectors can be used to select charged particles of a particular speed.

Marks:2

When particle moves in magnetic and electric field then to select charge,

Magnetic force on charge = Electric force on Charge • Q7

Identify the electromagnetic waves whose wavelength lie in the range

Write one use of each.

Marks:2

(a) Gamma rays fall in range of wavelength. They are used for the treatment of cancer.

(b)Infrared rays fall in range of wavelength. They are used in thermal imaging cameras.

• Q8

Draw the intensity pattern for a single slit diffraction and double slit interference. Hence, state two differences between interference and diffraction patterns.

Marks:2

The intensity pattern for a single slit diffraction is as shown below:

The intensity pattern for a double slit interference is as shown below:

Double Slit interference

Differences in the intensity patterns:

1. In interference, the region of minimum intensity is perfectly dark whereas in diffraction, it is not perfectly dark.

2. The width of fringes in interference is always equal. On the other hand, in diffraction, the width of fringes is never equal.

• Q9

Unpolarised light passed through a polaroid P1. When this polarized beam passes through another polaroid P2 and if the pass axis of P2 makes angle θ with the pass axis of P1, then write the expression for the polarized beam passing through P2. Draw a plot showing the variation of intensity when θ varies from 0 to 2π.

Marks:2

When an unpolarised light passes through polariser P1 , its intensity becomes I0/2 and light becomes polarised.

When this polarised light passes through P2 , then the intensity is given by “The Law Of Malus”

Now the intensity pattern is :