A parallel beam of light is incident normally on a plane surface absorbing 40% of the light and reflecting the rest. If the incident beam carries 60 W of power, the force exerted by it on the surface is

1. $3.2\times {10}^{-8} N$

2. $3.2\times {10}^{-7} N$

3. $5.12\times {10}^{-7} N$

4. $5.12\times {10}^{-8} N$

Calculate the energy of a photon with momentum $3.3\times 0^{-13} kg-m{s}^{-1}$, given Planck's constant to be $6.6\times {10}^{-34} Js$

1. $7.3\times {10}^4 J$

2. $9.9\times {10}^{-5} J$

3. $1.3\times {10}^5 J$

4. $8.1\times {10}^3 J$

Photons with energy 5 eV are incident on a cathode C in a photoelectric cell. The maximum energy of emitted photoelectrons is 2 eV. When photons of energy 6 eV are incident on C, no photoelectrons will reach the anode A, if the stopping potential of A relative to C is :

1.  +3V

2.  +4V

3.  -1V

4.  -3V

The photoelectric threshold wavelength of silver

is 3250 x 10^-10 m. The velocity of the electron

ejected from a silver surface by the ultraviolet

light of wavelength 2536 x 10^-10 m is :

(Given h= $4.14\times {10}^{-15} \mathrm{eVs}$ and $\mathrm{c}=3\times {10}^8 {\mathrm{ms}}^{-1}$)

1. $\approx 0.6\times {10}^{6}m{s}^{-1}$

2. $\approx 61\times {10}^{3}m{s}^{-1}$

3. $\approx 0.3\times {10}^{6}m{s}^{-1}$

4. $\approx 0.3\times {10}^{5}m{s}^{-1}$

A 5 W source emits monochromatic light of wavelength 5000 Å. When placed 0.5 m away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 m, the number of photoelectrons liberated will be reduced by a factor of:

1. 4

2. 8

3. 16

4. 2

The work function of the photosensitive material is 4.0 eV. The longest wavelength of light that can cause photoelectric emission from the substance is (approximately) :

1. 3100 nm

2. 966 nm

3. 31 nm

4. 310 nm

A proton and an $\alpha -$particle are accelerated from rest to the same energy. The de-Broglie wavelength ${\lambda }_p$ and ${\lambda }_{\alpha }$ are in the ratio:

1. 2:1

2. 1:1

3. $\sqrt{2}:1$

4. 4:1

A particle is dropped from a height H. The de-Broglie wavelength of the particle as a function of height is proportional to

1. H

2. H^1/2

3. H⁰

4. H^-1/2

The energy of a photon of green light of wavelength 5000 $\stackrel{0}{A}$ is-

1. $3.459\times {10}^{-19} J$

2. $3.973\times {10}^{-19 }J$

3. $4.132\times 0^{-19} J$

4. $8452\times {10}^{-19} J$

Consider a metal exposed to light of wavelength 600 nm. The maximum energy of the electron doubles when light of wavelength 400 nm is used. The work function in eV is:

1. 1.50 eV

2. 1.02 eV

3. 1.94 eV

4. 2.76 eV