21.

The ratio of amplitude of magnetic field to the amplitude of electric field for an electromagnetic wave propagating in vacuum is equal to

• the speed of light in vacuum

• the reciprocal of the speed of light in vacuum

• the ratio of magnetic permeability to the electric susceptibility of vacuum

• the ratio of magnetic permeability to the electric susceptibility of vacuum

If the momentum of an electron is chagned by p, then the de-Broglie wavelenght associated with it changes by 0.5%. The initial momentum of electron will be

• 200p

• 400p

• p/200

• p/200

A proton carrying 1 MeV kinetic energy is moving in a circular path of radius R in the uniform magnetic field. What should be the energy of an alpha particle to describe a circle of the same radius in the same field.

• 2 MeV

• 1 MeV

• 0.5 MeV

• 0.5 MeV

For the angle of minimum deviation of a prism to be equal to its refracting angle, the prism must be made of  a material whose refractive index

• Lies between 

• Lies between 2 and 

• is less than 1

• is less than 1

A rod of length  10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such way that it end closer to pole is 20  cm away from the mirror. The length of the image is

• 10 cm

• 15 cm

• 2.5 cm

• 2.5 cm

Two radiations of photon energies 1 eV and 2.5 eV, successively illuminate a photosensitive metallic surface of the maximum speeds of the emitted electrons is

• 1:4

• 1:2

• 1:1

• 1:1

The transition from the state n = 3 to n=1 in a hydrogen-like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition from.

• 2→ 1 

• 3 →2

• 4 → 2

• 4 → 2

The half-life to a radioactive nucleus is 50 days. The time interval (t₂-t₁) between the time t₂ when 2/3 of  it has decayed and the time t₁ when 1/3 of it had decayed is

• 30 days

• 50 days

• 60 days

• 15 days

The Input resistance of silicon transistor 100Ω. Base current is changed by 40 uA which results in a change in collector current by 2 mA. This transistor is used as common-emitter amplifier with a load resistance of 4 kΩ. The voltage gain of the amplifier is

• 2000

• 3000

• 4000

• 4000

To get an output Y = 1 in given circuit which of the following input will be correct

• A	B	C
  1	0	0

• A	B	C
  1	0	1

• A	B	C
  1	1	0

• A	B	C
  1	1	0