# Calculating the energy of light

1. Oct 18, 2007

### wisdom32

Okay, im doing experiments on calculating the energy of light by measuring the voltage on a voltmeter. Now, im varying the wavelength of the light by using filters of different colours. Will i be able to get different readings if i use a milivoltmeter ? Also, once ive gotten the readings in voltage, how can i convert them to joules ?

P/s : What does the INF mean on a resistance box ?

Thanks.

2. Oct 18, 2007

### Chi Meson

It depends on what kind of cell you are using to detect the light (size and material, multiple cells in series etc.), and on the method you employ, but you should generally require an ability to measure up to a 0.5 volt or full volts. (Look up "stopping potentials" under photoelectric effect).

See if you can use an electronic multi-meter, one that can switch between different orders of magnitude

See if you can find filters that come with spectrum charts that indicate the intensity of transmission of each wavelength of light. Available from many drama departments (for stage-lighting filters).

"INF" probably means "infinite resistance," a fancy word for off.

3. Oct 19, 2007

### wisdom32

does solar cell the dimension of 10cm x 10 cm differ from a photocell ? when a solar cell that receives light from a sun is called solar cell and any other light source would be called photo cell , is that right ? thanks

4. Oct 19, 2007

### Chi Meson

Something called a photocell might be a "photoresistor." And a photoresistor could be one of two kinds. There are the photoresistors that will decrease their resistance as the intensity of light is increased, and there are photoresistors that will increase the resistance as intensity is increased.

A solar cell will usually be a straightforward "phtotelectric effect" voltaic cell. It could again be called a photocell; this word does to seem to have an absolute definition. In this latter case, the maximum voltage produced will be proportional to the maximum frequency of the incident light.

Without knowing more particulars about the cell you are using, you might have a difficult time measuring the absolute energy of the incident light. You could use any of these to measure the proportional changes of energy in the light as the color changes.

5. Oct 20, 2007

### wisdom32

im planning to measure the maximum power by plotting a graph of current against voltage. i dont think this circuit if mine is right
http://img99.imageshack.us/img99/9167/97481115ua3.th.jpg [Broken]

because ive been getting 0V when the resistance box is turned on. but when i remove the resistance box, the voltmeter shows reading. how am i to set up the right and correct circuit ?

Last edited by a moderator: May 3, 2017
6. Oct 24, 2007

### wisdom32

please can anyone help me ?