Question

Photoelectrons with a maximum speed of 8.00 × 107 m/s are ejected from a surface in the presence of light with a frequency of 7.50 × 1014Hz. If the mass of an electron is 9.10 × 10-31 kg, calculate the maximum kinetic energy of a single electron, in joules.
7.28 × 10-23 J
5.82 × 10-15 J
2.91 × 10-15 J
3.41 × 10-16 J

Answer 1

KE = 1/2 * mass * velocity^2
KE = 1/2 * 9.10x10^-31 * (8.00x10^7)^2
KE = 1/2 * 9.10x10^-13 * 6.4x10^15
KE = 2.912x10^-15 J or C

Answer 2

Answer:

Maximum kinetic energy, $E_k=2.91\times 10^{-15}\ J$

Explanation:

It is given that,

Speed of photoelectrons, $v_{max}=8\times 10^7\ m/s$

Mass of electrons, $m=9.1\times 10^{-31}\ Kg$

Frequency of light, $\nu=7.5\times 10^{14}\ Hz$

According to Einstein equation :

$h\nu=h\nu_o+\dfrac{1}{2}mv_{max}^2$

Where

υ is frequency of radiation

υ₀ is the threshold frequency

Maximum kinetic energy of single electron is, $E_k=\dfrac{1}{2}mv_{max}^2$

$E_k=\dfrac{1}{2}\times 9.1\times 10^{-31}\times (8\times 10^7)^2$

$E_k=2.91\times 10^{-15}\ J$

Hence, the correct option is (C) " $2.91\times 10^{-15}\ J$ "