# Threshold frequency

1. Jan 26, 2005

### Gogsey

What is the equation used to solve for the threshold frequency?

Is the threshold frequency the minimum amount of energy requird to free an electron from the nucleus?

2. Jan 26, 2005

### Sirus

$$W=hf_{0}$$

where $W$ is the work function, $h$ is Planck's constant, and $f_{0}$ is the threshold frequency. I believe the answer to your second question is yes.

3. Jan 27, 2005

### rgshankar76

We talk of threshold frequency because the energy of the photon is h*f. That energy should be sufficient enough to knock out the electron.

4. Jan 29, 2005

### maverick280857

To be precise this is just sufficient energy to bring an electron to the surface but not quite to knock it out of the metal. (Again this depends on how you interpret "knock out"). Thats why in the so called Einstein equation for photoelectric effect, there's a second term which accounts for the kinetic energy of the ejected photoelectron...if this term were zero, the electron would--in principle--stay there.

5. Jan 29, 2005

### Sirus

That is true. The full equation is

$$E_{photon}=W+E_{K}_{max}$$

As you can see, the equation for $W$ as a function of threshold frequency is derived from this by setting the kinetic energy of the photoelectron to zero.

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