How to find planks constant from a given graph?

by phys02
Tags: constant, graph, planks
phys02 is offline
Apr18-10, 07:17 AM
P: 4
Hi everyone, I can't seem to calculate Planks constant (h) from this graph. I thought it should simply be the gradient? So I used h= (f1-f2)/(Ua-Ua2) but found it to be nothing near the actual constant of 6.63*10^34!
Any help would be greatly appreciated!
Attached Thumbnails
Phys.Org News Partner Science news on
Simplicity is key to co-operative robots
Chemical vapor deposition used to grow atomic layer materials on top of each other
Earliest ancestor of land herbivores discovered
jeppetrost is offline
Apr18-10, 07:39 AM
P: 88
It depends on what the graph is showing.
When U is in volts, you can't use U = h*f, since U isn't the energy.
RoyalCat is offline
Apr18-10, 11:42 AM
P: 672
I'm assuming [tex]U_a[/tex] is the stopping potential.

Derive the relationship between the stopping potential and the frequency of the photons in a photoelectric effect experiment.

I'll help you get started, the stopping potential is that potential at which an electron with maximal kinetic energy cannot reach the other electrode. It doesn't have enough energy. Contemplate what energy it leaves the metal with, and how much energy it has left as it approaches the second electrode, and where that energy goes, and you should have your answer.

From there, the relationship between the stopping potential and frequency shown in the graph should be straight-forward to deduce. You're only off by a factor of the electron charge (e=1.602 * 10^-19 C)

Register to reply

Related Discussions
finding planks constant from photoelectric effect Introductory Physics Homework 6
Planks Constant Introductory Physics Homework 3
planks length to planks volume? Quantum Physics 2