Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A laser pointer sends out mW of red light of wavelength nm. A photocell catches all of the light, and of the photons free an electron. Use eV nm and C. Find (a) the energy of one photon, (b) the number of photons each second and (c) the photocurrent.
A photon has energy , with eV nm. Einstein's equation is . So , a straight line of slope V s. A beam of power sends photons each second.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. One photon. .
Step 2. Photons each second. W, so .
Step 3. Electrons each second. .
Step 4. The current. .
Answer: eV; photons each second; .
Check. If every photon freed an electron, the current would be 500 times larger: mA.
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