## Threshold Frequency

Areena H 2K
Posts: 81
Joined: Wed Dec 05, 2018 12:18 am

### Threshold Frequency

Can someone clarify on the threshold frequency? Is it the work function times planck's constant?

SarahCoufal_1k
Posts: 102
Joined: Thu Jul 25, 2019 12:17 am

### Re: Threshold Frequency

I believe Threshold Frequency is the amount of energy of a photon required to displace an electron on a metal surface. The photon needs to at least match the threshold, which will result in a kinetic energy of 0.

Areena H 2K
Posts: 81
Joined: Wed Dec 05, 2018 12:18 am

### Re: Threshold Frequency

Sarah_Coufal_3k wrote:I believe Threshold Frequency is the amount of energy of a photon required to displace an electron on a metal surface. The photon needs to at least match the threshold, which will result in a kinetic energy of 0.

Yes that part makes sense to me but when we're calculating the threshold frequency, is it work function times planck's constant or something else?

Lindsey Chheng 1E
Posts: 110
Joined: Fri Aug 30, 2019 12:16 am

### Re: Threshold Frequency

Areena H 3F wrote:
Sarah_Coufal_3k wrote:I believe Threshold Frequency is the amount of energy of a photon required to displace an electron on a metal surface. The photon needs to at least match the threshold, which will result in a kinetic energy of 0.

Yes that part makes sense to me but when we're calculating the threshold frequency, is it work function times planck's constant or something else?

Threshold Energy is also known as the Work Function, so to calculate threshold energy, we use this equation:
E(photon) - E(energy to remove an e-) = E(excess) ...which can also be expressed as ... E(hv) - (work function) = Ek(1/2 mv)
Work function is expressed in J because it is the amount of energy needed to remove an electron from a metal surface; sometimes it's given in a question, and sometimes you have to solve for it using the above equation and plugging in values you do know for the other variables.

Jasmine 2C
Posts: 184
Joined: Wed Sep 18, 2019 12:18 am

### Re: Threshold Frequency

Threshold energy for the photoelectric effect (shining light on a metal surface and observing whether or not electrons were ejected) is the minimum amount of energy required to remove an electron from the metal surface. Threshold frequency would then be the minimum frequency of the light that gives off the minimum amount of energy needed to remove the electron. Usually, they describe energy as "threshold" because the frequency of light can be greater (thus greater energy than the threshold) and the excess energy would be defined as kinetic energy.

kristi le 2F
Posts: 102
Joined: Thu Jul 11, 2019 12:15 am

### Re: Threshold Frequency

The threshold frequency is synonymous with work function, which is the Energy needed to remove an electron. However, each individual photon must reach this threshold frequency, dependent on wavelength, not intensity. Therefore, light is acting like a particle, not like in the wave model.