- #1

lpettigrew

- 115

- 10

- Homework Statement
- I have found the multiple choice question below but cannot deliberate upon a solution, and am sure there is a problem with my workings. Could anyone help me here?

What is the maximum velocity of an electron emitted from lanthanum under a light of wavelength 150 nm?

A. 1.3 x 10^-3 ms-1

B. 1.3 x 10^3 ms-1

C. 1.3 x 10^6 ms-1

D. There is not sufficient energy to emit an electron.

- Relevant Equations
- 1/2 mv^2 max = hf - Φ

E=hf

Mass of an electron = 9.1*10^-31

Well, to find the maximum kinetic energy of the electron use E=hf, E=hc/λ=6.63*10^-34*3*10^8/1.5 *10^-7

E=1.326 *10^-18 J

1/2m v^2 max=E

Rearrange in terms of v:

v=√2E/m

v=√2*1.326 *10^-18/ *9.1*10^-31

v=1707127... ~ 171000 ms^-1

Where have I gone wrong here?

Well, to find the maximum kinetic energy of the electron use E=hf, E=hc/λ=6.63*10^-34*3*10^8/1.5 *10^-7

E=1.326 *10^-18 J

1/2m v^2 max=E

Rearrange in terms of v:

v=√2E/m

v=√2*1.326 *10^-18/ *9.1*10^-31

v=1707127... ~ 171000 ms^-1

Where have I gone wrong here?