Q. The electric field associated with a light wave is given by E = E_{0 }sin[(1.57 × 10^{7})(x – ct)] . Find the stopping potential when this light is used in an experiment on photoelectric effect with the emitter having work function 1.9 eV

(a) 1.2 V

(b) 1.1 V

(c) 2V

(d) 2.1 V

Ans: (a)

Sol: On comparing with equation ,

E = E_{0 }sin(kx − ωt)

ω = 1.57× 10^{7 }c

⇒ 2πν = 1.57 × 10^{7} × 3 × 10^{8}

ν =( 1.57 × 10^{7} × 3 × 10^{8} )/2π

A/c to Einstein’s photoelectric equation

hν = φ + K_{max}

⇒ hν = φ + eV_{0}

V_{0} = ( hν − φ)/e

On putting standard values we get ,

V_{0} = 1.2 volt