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

To Access the full content, Please Purchase

• Q1

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.

• Q2

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.

• Q3

What is the direction of induced currents in metal rings 1 and 2 when current I in the wire is increasing steadily?

Marks:1

The direction of induced currents in both the ring can be predictedusing Lenz’s lens.

As, induced current opposes the cause of increasing of magnetic flux. So, it will be clockwise in ring 1 and anticlockwise in ring 2.

• Q4

In which directions do the electric and magnetic field vectors oscillate in an electromagnetic wave propagating along the x-axis?

Marks:1

The electric and magnetic field vectors will be in the Y-Z plane. They will be mutually perpendicular.

• Q5

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

H = I2Rt,is known as Joule’s law of heating.

Where H is the amount of heat produced when a current I flows through a conductor of resistance R for a time t. In joule’s law of heating, H is directly proportional to resistance of the material. Hence, nichrome offers higher resistance than copper wire, so, it will heat-up faster.

• Q6

Write two properties of a material suitable for making (a) a permanent magnet, and (b) an electromagnet.

Marks:2

(a) Permanent magnets are made up of the materials which have high retentivity and high coercivity.

(b)Electromagnets are made up of the materials which have high permeability and low retentivity.

• Q7

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.

• Q8

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 :

• Q9

Why does current in a steady state not flow in a capacitor connected across a battery? However momentary current does flow during charging or discharging of the capacitor. Explain.

Marks:2

Initially,the capacitor is uncharged. When it is connected across a battery,(top plate of the capacitor is connected to the positive terminal of the battery and the bottom plate is connected to the negative terminal) positive charge starts to accumulate on the top plate of the capacitor and negative charge begins to accumulate on the bottom plate. At steady state capacitor becomes fully charged with voltage equal to the supply voltage,hence from now it behaves like open circuit as net voltage in circuit is zero so current is also equal to zero.

So, when an uncharged capacitor is connected to a battery, current flows for a very short duration, until the capacitor is fully charged, and then flow of current stops.