## Kinetic Energy

H-Atom ($E_{n}=-\frac{hR}{n^{2}}$)

Kennedi2J
Posts: 101
Joined: Wed Sep 18, 2019 12:20 am

### Kinetic Energy

In the equation, E= work function + KE (kinetic energy), how do we know when kinetic energy is equal to 0?

Lelija Kazlauskas 3J
Posts: 50
Joined: Thu Jul 11, 2019 12:16 am

### Re: Kinetic Energy

Kinetic energy is equal to (1/2)mv^2, so the result must always be either positive or zero (which would be if either v or m were equal to 0).

Posts: 104
Joined: Fri Aug 09, 2019 12:16 am

### Re: Kinetic Energy

There is kinetic energy when the energy of the photons being aimed at the metal is greater than the work function. Therefore, if the energy of the photon is equal to the work function there is no kinetic energy. The kinetic energy is the excess energy from the photon therefore if there is no excess (they are equal to each other) then there is no kinetic energy.

Keerthana Sivathasan 2E
Posts: 101
Joined: Wed Sep 18, 2019 12:22 am

### Re: Kinetic Energy

Instead use E(kinetic)=hf-(work function) to see when kinetic energy is equal to 0.

pmokh14B
Posts: 107
Joined: Sat Aug 17, 2019 12:15 am

### Re: Kinetic Energy

Kinetic energy is zero when the work function iis equal to the energy of the photon hitting the metal. If a problem asks how much energy is required to eject an electron from a surface of the metal you would also make KE equal to zero.