Science (English Medium) Class 12 - CBSE Important Questions for Physics

Define a wavefront.

Write two important advantages of reflecting telescope over a refracting telescope.

Why are infra-red waves often called heat waves? Explain.

Write the S.I. unit of mutual inductance.

State the two Kirchhoff’s rules used in electric networks. How are there rules justified?

In a single slit diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of the central diffraction band?

Define electric flux.

Four point charges Q, q, Q and q are placed at the corners of a square of side 'a' as shown in the figure.

Find the

1) resultant electric force on a charge Q, and

2) potential energy of this system.

A 10 V cell of negligible internal resistance is connected in parallel across a battery of emf 200 V and internal resistance 38 Ω as shown in the figure. Find the value of current in the circuit.

State Ampere’s circuital law.

The susceptibility of a magnetic material is 0·9853. Identify the type of magnetic material. Draw the modification of the field pattern on keeping a piece of this material in a uniform magnetic field.

The teachers of Geeta’s school took the students on a study trip to a power generating station, located nearly 200 km away from the city. The teacher explained that electrical energy is transmitted over such a long distance to their city, in the form of alternating current (ac) raised to a high voltage. At the receiving end in the city, the voltage is reduced to operate the devices. As a result, the power loss is reduced. Geeta listened to the teacher and asked questions about how the ac is converted to a higher or lower voltage.

1) Name the device used to change the alternating voltage to a higher or lower value. State one cause for power dissipation in this device.

2) Explain with an example, how power loss is reduced if the energy is transmitted over long distances as an alternating current rather than a direct current.

3) Write two values each shown by the teachers and Geeta.

Name the electromagnetic radiations used for (a) water purification, and (b) eye surgery.

The figure shows a ray of light falling normally on the face AB of an equilateral glass prism having refractive index`3/2`, placed in water of refractive index `4/3`.Will this ray suffer total internal reflection on striking the face AC? Justify your answer.

When a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle. Explain why?

State Huygen’s principle.

If one of two identical slits producing interference in Young’s experiment is covered with glass, so that the light intensity passing through it is reduced to 50%, find the ratio of the maximum and minimum intensity of the fringe in the interference pattern.

Using Huygens’ principle, verify the laws of reflection at a plane surface.

If light of wavelength 412.5 nm is incident on each of the metals given below, which ones will show photoelectric emission and why?

A hydrogen atom initially in the ground level absorbs a photon, which excites it to the n = 4 level. Determine the wavelength and frequency of the photon.