Science (English Medium) Class 12 - CBSE Question Bank Solutions for Physics

There are two sources of light, each emitting with a power of 100 W. One emits X-rays of wavelength 1 nm and the other visible light at 500 nm. Find the ratio of number of photons of X-rays to the photons of visible light of the given wavelength?

The simple Bohr model is not applicable to He 4 atom because ______.

1. He⁴ is an inert gas.
2. He⁴ has neutrons in the nucleus.
3. He⁴ has one more electron.
4. electrons are not subject to central forces.

Imagine removing one electron from He⁴ and He³. Their energy levels, as worked out on the basis of Bohr model will be very close. Explain why.

If the magnetizing field on a ferromagnetic material is increased, its permeability ______.

A uniform magnetic field gets modified as shown in figure when two specimens A and B are placed in it.

(a)	(b)

1. Identify the specimen A and B.
2. How is the magnetic susceptibility of specimen A different from that of specimen B?

The curve of binding energy per nucleon as a function of atomic mass number has a sharp peak for helium nucleus. This implies that helium nucleus is ______.

• Assertion (A): Diamagnetic substances exhibit magnetism.
• Reason (R): Diamagnetic materials do not have a permanent magnetic dipole moment.

Define the critical angle for a given pair of media and total internal reflection. Obtain the relation between the critical angle and refractive index of the medium.

Calculate the self-inductance of a coil using the following data obtained when an AC source of frequency `(200/pi)` Hz and a DC source are applied across the coil.

A point object in the air is placed symmetrically at a distance of 60 cm in front of a concave spherical surface with a refractive index of 1.5. If the radius of curvature of the surface is 20 cm, find the position of the image formed.

The energy of a photon of wavelength 663 nm is ______.

Which of the following has a permeability less than that of free space?

The energy of a photon of wavelength λ is ______.

• Assertion (A): The deflecting torque acting on a current-carrying loop is zero when its plane is perpendicular to the direction of the magnetic field.
• Reason (R): The deflecting torque acting on a loop of the magnetic moment `vecm` in a magnetic field `vecB` is given by the dot product of `vecm` and `vecB`.

A current of 1A flows through a coil when it is connected across a DC battery of 100V. If the DC battery is replaced by an AC source of 100 V and angular frequency of 100 rad s^-1, the current reduces to 0.5 A. Find

1. the impedance of the circuit.
2. self-inductance of coil.
3. Phase difference between the voltage and the current.

The primary coil having N_P turns of an ideal transformer is supplied with an alternating voltage V_P. Obtain an expression for the voltage V_S induced in its secondary coil having N_S turns.

Mention two main sources of power loss in real transformers.

Which of the following cannot modify an external magnetic field as shown in the figure?

The relative magnetic permeability of a substance X is slightly less than unity and that of substance Y is slightly more than unity, then ______.

The large scale transmission of electrical energy over long distances is done with the use of transformers. The voltage output of the generator is stepped-up because of ______.