 #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 ms1
B. 1.3 x 10^3 ms1
C. 1.3 x 10^6 ms1
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?