## Threshold Energy Question

Drake_Everlove_1K
Posts: 19
Joined: Sat Sep 24, 2016 3:02 am

### Threshold Energy Question

Hi,

So I am a bit perplexed by the following equation, which is apparently true in both instances:

hv = threshold energy

hv = threshold energy + 1/2mv^2

(1/2mv^2 = kinetic energy)

In the first equation, the energy of what is being solved for?
In the second equation, what energy is being solved for?

How are both equations true? The second one just adds a variable. I'm so confused how they can both be true.

Junghyuk_Park_1I
Posts: 34
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Threshold Energy Question

The first equation is used when an electron has not been ejected with an exit velocity off of the solid metal once the light source hits it. The second equation is used when the electrons have been ejected with a kinetic energy (which implies velocity). Basically, both equations are talking about the same thing, just different situations (electrons being ejected and not ejected). I hope this helps!