In a photocell bichromatic light of wavelength 2475 mathringA and 6000 mathringA are incident on cathode whose work function is 4.8 eV. If a uniform magnetic field of 3 × 10-5 Tesla exists parallel to the plate, the radius of the path describe by the photoelectron will be (mass of electron .=9 × 10-31 kg )

Question

In a photocell bichromatic light of wavelength 2475 mathringA and 6000 mathringA are incident on cathode whose work function is 4.8 eV. If a uniform magnetic field of 3 × 10-5 Tesla exists parallel to the plate, the radius of the path describe by the photoelectron will be (mass of electron .=9 × 10-31 kg ) (A) 1 cm (B) 5 cm (C) 10 cm (D) 25 cm

Tardigrade Admin · Accepted Answer

Energy of photons corresponding to light of wavelength

λ_{1} = 2475 \overset{˚}{A}

is

E_{1} = \frac{12375}{2475} = 5 e V

and that corresponding to

λ_{2} = 6000 \overset{˚}{A}

is

E_{2} = \frac{12375}{6000} = 2.06 e V

As

E_{2}^{'} < W_{0}

and

E_{1} > W_{0}

Photoelectric emission is possible with

λ_{1}

only. Maximum kinetic energy of emitted photoelectrons

K = E - W_{0} = 5 - 4.8 = 0.2 e V

Photoelectrons experience magnetic force and move along a circular path of radius

r = \frac{2 mk}{QB} = \frac{2 \times 9 \times 1 0 ^{- 31} \times 0.2 \times 1.6 \times 1 0 ^{- 19}}{1.6 \times 1 0 ^{- 19} \times 3 \times 1 0 ^{- 5}}

= 0.05 m = 5

cm

Q. In a photocell bichromatic light of wavelength 2475A˚ and 6000A˚ are incident on cathode whose work function is 4.8eV. If a uniform magnetic field of 3×10−5 Tesla exists parallel to the plate, the radius of the path describe by the photoelectron will be (mass of electron =9×10−31kg)

1 cm

5 cm

10 cm

25 cm