photoelectric effect (1 Viewer)

[edd91]

Is it true to say, that if you had a photoelectric probe on a data logger and compared lights of varying frequncy but same intensity, the current should be same, assuming the work function of the probe is below the lowest frequency colour you use

 

[Calculon]

Intensity changes current
Frequency changes voltage
This works according to the quantum theory of light

 

[edd91]

Yep, so different colours at same frequency will have same reading on the data logger, because it measures current, right??
Sweet

 

[George W. Bush]

no - if I'm not wrong, the same intensity of light would be the same amount of energy radiated per unit time. However, higher frequency lights emit photons of more energy, thus emit less photons per second - meaning less photons can be liberated.

For example, if we have two lights of 20 units intensity - a red and a blue. The red one emits, say, 20 photons (1 unit energy each), and the blue emits 5 (4 units energy each).

The red light can liberate 20 electrons, while the blue can only liberate 5 (with a greater max KE)

 

[Zarathustra]

Originally posted by George W. Bush
no - if I'm not wrong

You're never wrong

 

[edd91]

Originally posted by George W. Bush
no - if I'm not wrong, the same intensity of light would be the same amount of energy radiated per unit time. However, higher frequency lights emit photons of more energy, thus emit less photons per second - meaning less photons can be liberated.

For example, if we have two lights of 20 units intensity - a red and a blue. The red one emits, say, 20 photons (1 unit energy each), and the blue emits 5 (4 units energy each).

The red light can liberate 20 electrons, while the blue can only liberate 5 (with a greater max KE)

Oh really?
Are you sure? Dont meen to sound cynical, but isn't the intensity just the amount of photons given off?

 

[edd91]

George W. I hate to say this but I think you'rw wrong, intensity is purely the flux of photons, its independant to frequency

 

[Xayma]

Originally posted by edd91
Yep, so different colours at same frequency will have same reading on the data logger, because it measures current, right??
Sweet

Different colours of light have difference frequencies.

Intensity is the amount of photons released per unit time.

The energy of each individual photon is only dependent on its frequency (from E=h/f).

 

[edd91]

Originally posted by Xayma
Different colours of light have difference frequencies.

Intensity is the amount of photons released per unit time.

The energy of each individual photon is only dependent on its frequency (from E=h/f).

Yess, so two lights (blue and red) of the same intensity would produce the same current assuming the metal will liberate electrons to both these colours?
http://lectureonline.cl.msu.edu/~mmp/kap28/PhotoEffect/photo.htm
Why does this applet increase current with frequency then its really confusing me

 

[Xayma]

It shouldnt change, each electron can only absorb one photon, and since the charge on an electron is constant, then the current will be constant (once it is at equilibrium between amount of photons being emitted and electrons reaching the other side)

 

[Calculon]

Work with the one photon, one electron idea:

- each photon can only knock off one electron
- a photon must have a certain energy before it can knock off an electron (and hence a higher frequency, since E=hf)
- intensity is the number of photons
- frequency is the energy of photons

 

[edd91]

So whats the go with the applet

 

[Xayma]

The applet is wrong. Notice that as you decrease the voltage the current decreases this is not the case experimentally (if you have done the experiment you will see it), the current decreases rapidly with the voltage near the end.

 

[t-i-m-m-y]

no - if I'm not wrong, the same intensity of light would be the same amount of energy radiated per unit time. However, higher frequency lights emit photons of more energy, thus emit less photons per second - meaning less photons can be liberated.

For example, if we have two lights of 20 units intensity - a red and a blue. The red one emits, say, 20 photons (1 unit energy each), and the blue emits 5 (4 units energy each).

The red light can liberate 20 electrons, while the blue can only liberate 5 (with a greater max KE)

hey edd.. this was something along the lines of what i was trying to say in the OCAU forums. nothing other than what he/she said.