A light beam of wavelength 500 nm is incident on a metal having work function of 1.25 eV, placed in a magnetic field of intensity B. The electrons emitted perpendicular to the magnetic field B, with maximum kinetic energy are bent into circular arc of radius 30 cm. The value of B is × 10-7 T Given h c=20 × 10-26 J -m, mass of electron =9 × 10-31 kg

Question

A light beam of wavelength 500 nm is incident on a metal having work function of 1.25 eV, placed in a magnetic field of intensity B. The electrons emitted perpendicular to the magnetic field B, with maximum kinetic energy are bent into circular arc of radius 30 cm. The value of B is × 10-7 T Given h c=20 × 10-26 J -m, mass of electron =9 × 10-31 kg (A)  (B)  (C)  (D)

Tardigrade Admin · Accepted Answer

By photoelectric equation (h c/λ)-φ=k max k max =(1240/500)-1.25 ≈ 1.25 r=(√2 m k/e B) B=(√2 m k/e r) =125 × 10-7 T

By photoelectric equation λhc​−ϕ=kmax​ kmax​=5001240​−1.25≈1.25 r=eB2mk​​ B=er2mk​​ =125×10−7T

By photoelectric equation
$\frac{h c}{λ} - ϕ = k_{m a x}$
$k_{m a x} = \frac{1240}{500} - 1.25 \approx 1.25$
$r = \frac{2 mk}{e B}$
$B = \frac{2 mk}{er}$
$= 125 \times 1 0^{- 7} T$