Dual Nature of Radiation and Matter · Question 43

A 200 W sodium street lamp emits yellow light of wavelength 0.6 . Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

1. 1.5 1020
2. 6 1018
3. 62 1020
4. 3 1019

Monochromatic radiation emitted when electron in hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be 3.57 V. The threshold frequency of the material is

1. 4 1015 Hz
2. 5 1015 Hz
3. 1.6 1015 Hz
4. 2.5 1015 Hz

An -particle moves in a circular path of radius 0.83 cm in the presence of a magnetic field of 0.25 Wb/m2. The de Broglie wavelength associated with the particle will be

1. 1 A
2. 0.1 A
3. 10 A
4. 0.01 A

The threshold frequency for a photosensitive metal is 3.3 1014 Hz. If light of frequency 8.2 1014 Hz is incident on this metal, the cut-off voltage for the photoelectron emission is nearly

1. 1 V
2. 2 V
3. 3 V
4. 5 V

Photoelectric emission occurs only when the incident light has more than a certain minimum

1. power
2. wavelength
3. intensity
4. frequency

Light of two different frequencies whose photons have energies 1 eV and 2.5 eV respectively illuminate a metallic surface whose work function is 0.5 eV successively. Ratio of maximum speeds of emitted electrons will be

1. 1 : 4
2. 1 : 2
3. 1 : 1
4. 1 : 5

Electrons used in an electron microscope are accelerated by a voltage of 25 kV. If the voltage is increased to 100 kV, then the de Broglie wavelength associated with the electrons would

1. increase by 2 times
2. decrease by 2 times
3. decrease by 4 times
4. increase by 4 times

In photoelectric emission process from a metal of work function 1.8 eV, the kinetic energy of most energetic electrons is 0.5 eV. The corresponding stopping potential is

1. 1.8 V
2. 1.3 V
3. 0.5 V
4. 2.3 V

In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by

1. increasing the potential difference between the anode and filament
2. increasing the filament current
3. decreasing the filament current
4. decreasing the potential difference between the anode and filament

A radioactive nucleus of mass M emits a photon of frequency and the nucleus recoils. The recoil energy will be

1. Mc2 - h
2. h2 2/2Mc2
3. zero
4. h