Question

83Bi214 83ndergoes a beta minus decay. Its daughter then alpha decays. What remains? (A) 84Po214 (C) oHg0 (E) 8,Bi209 (B) 82Pb210 (D) 86Rn210 Copper has a work function of 48 eV. What wavelength of the electro- magnetic spectrum will produce photoelectrons with the lowest kinetic energy? (A) 4.1 x 10-26 m (B) 9.5 x 10-25 m (C) 2.6 x 10-7 m (D) 1.3 x 10-6 m (E) 5.8 x 10-7 m

Answer 1

(1) ²¹⁴Bi₈₃ which undergoes a beta minus decay.

²¹⁴Bi₈₃ $\overset{\beta -}{\rightarrow}$ ²¹⁴Po₈₄

Its daughter then alpha decays. What remains?

²¹⁴Po₈₄ $\overset{\alpha }{\rightarrow}$ ²¹⁰Pb₈₂

Option (B) : it will be correct.

(2) We know that, Copper has a work function of 4.8 eV.

converting eV into J :

_$\varphi$ = [(4.8 eV) (1.6 x 10^-19 J/eV)]

_$\varphi$ = 7.68 x 10^-19 J

What wavelength of an electromagnetic spectrum will produce photoelectrons with the lowest kinetic energy?

using a formula, we have

$\lambda$ = h c / _$\varphi$

where, h = planck's constant = 6.63 x 10^-34 J.s

c = speed of light = 3 x 10⁸ m/s

then, we get

$\lambda$ = [(6.63 x 10^-34 J.s) (3 x 10⁸ m/s)] / (7.68 x 10^-19 J)

$\lambda$ = [(1.989 x 10^-25 J.m) / (7.68 x 10^-19 J)]

$\lambda$ = 2.589 x 10^-7 m

$\lambda$ = 2.6 x 10^-7 m

Option (C) : it will be correct.