Electromagnetic Waves — Physics STD 12 Science — Question

Mark out the correct options.

1. Diamagnetism occurs in all materials.
2. Diamagnetism results from the partial alignment of permanent magnetic moment.
3. The magnetizing field intensity H is always zero in free space.
4. The magnetic field of induced magnetic moment is opposite to the applied field.

When light is refracted into a medium:

1. Its wavelength and frequency both increase
2. Its wavelength increases but frequency remains unchanged
3. Its wavelength decreases but frequency remains unchanged.
4. Its wavelength and frequency both decrease.

An object 2.5 cm high is placed at a distance of 10 cm   from a concave mirror of radius of curvature 30 cm  The size of the image is

(a) 9.2 cm

(b) 10.5 cm

(c) 5.6 cm

(d) 7.5 cm

A student plots a graph from his reading on the determination of Young modulus of a metal wire but forgets to put the labels. the quantities on X and Y axes may be respectively:

1. Weight hung and length increased.
2. Stress applied and length Increased.
3. Stress applied and strain developed.
4. Length increased and the weight hung.

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In the circuit shown here, E₁ = E₂ = E₃ = 2 V and R₁ = R₂ = 4 ohms.  The current flowing between points A and B through battery E₂ is

(a) Zero	(b) 2 amp from A to B
(c) 2 amp from B to A	(d) None of the above

Between the plates of a parallel plate condenser there is 1mm thick paper of dielectric constant 4. It is charged at 100 volt. The electric field in volt/metre between the plates of the capacitor is

(a) 100

(b) 100000

(c) 25000

(d) 4000000

A metallic loop is placed in a magnetic field. If a current is passed through it, then

(a) The ring will feel a force of attraction

(b) The ring will feel a force of repulsion

(c) It will move to and fro about its centre of gravity

(d) None of these

Tungsten has work function 4.8 eV. We wish to use tungsten as photo-cathode with a 600 nm wavelength. What shall we do?

When radiation of wavelength   is incident on a metallic surface, the stopping potential is 4.8 volts. If the same surface is illuminated with radiation of double the wavelength, then the stopping potential becomes 1.6 volts. Then the threshold wavelength for the surface is

(a) 2

(b) 4

(c) 6

(d) 8

The work function of aluminium is 4.2 eV.If two photons each of energy 3.5 eV strike an electron of aluminium, then emission of electrons will be: