# Does a photo-resistor create an AC current?

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1. Jan 25, 2016

### grahas

I'm a high school physics student. I want to do an experiment to see what happens when a high frequency alternating current goes through a magnet. To create the high frequency alternating current could a photo resistor do that for me? Does the photo-resistor create an alternating current with a frequency equal to the light hitting it?

2. Jan 25, 2016

### axmls

No, a photoresistor can only change the value of its resistance depending on the light level, and the frequency of the light doesn't produce an alternating effect.

You could vary between lower current and higher current with a photo resistor and a battery, but that's not exactly what you're asking for (the current would never go negative). Furthermore, I don't even think photoresistors respond quickly enough to alternate the current at even moderate frequencies.

3. Jan 25, 2016

### grahas

Is there any way to achieve an alternating current with a frequency in the range of light, via a mechanical or electrical device?

4. Jan 25, 2016

### axmls

Not to my knowledge. The frequency of light is much, much bigger than, say, microwave frequencies.

5. Jan 25, 2016

### grahas

Well, I'll post back the results of my experiment to close the thread, thanks for the help!

6. Jan 25, 2016

### meBigGuy

Are you saying you want to use the magnet as a conductor? I don't think anything is going to happen. What would you like to see happen?

As for high frequency AC, your wifi network runs at 2.4GHz. Low frequency (red) light is 400,000 GHz.
http://www.laserfocusworld.com/articles/print/volume-49/issue-07/newsbreaks/world-s-fastest-photodetector-has-70-ghz-bandwidth.html [Broken]
Photodetectors respond to the amplitude of the light, not the light frequency

Nothing electrical directly responds at the frequency of light.

Last edited by a moderator: May 7, 2017
7. Jan 26, 2016

### davenn

other than short circuiting the power supply

to the OP ..... definitely not a wise thing to do

8. Jan 26, 2016

### Staff: Mentor

A radio transmitter does that. Just put your magnet next to a cell phone while talking.

What effects would you see? Probably nothing.

9. Jan 26, 2016

### davenn

yes, the standard way is to apply the correct amount of voltage to an appropriate light globe or LED ( Light Emitting Diode)

10. Jan 26, 2016

### meBigGuy

Note that does not actually create a 400,000 GHz AC current (electron flow). It creates a stream of photons with a frequency of 400,000 GHz

11. Jan 26, 2016

### davenn

yes, I realise that ... but it's about the closest he is going to get

12. Jan 27, 2016

### meBigGuy

I got it, and was sure you knew. Just wanted him to be clear.

13. Jan 27, 2016

### davenn

I'm not aware of any way to do what he is asking. Even in the GHz microwave bands above around 30 GHz and up to several 100 GHz,
any oscillation within a Gunn diode or similar device, doesn't as an oscillation of electrons at that freq occur outside the device ( to my knowledge)

Dave

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