A-level Physics (Advancing Physics)/Light as a Quantum Phenomenon/Worked Solutions

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1. How much energy does a photon with a frequency of 50 kHz carry?

2. A photon carries 10−30J of energy. What is its frequency?

3. How many photons of frequency 545 THz does a 20W monochromatic bulb give out each second?

First calculate the amount of energy given out per. second:

Then, calculate the amount of energy carried by each photon:

Then divide the former by the latter to give the number of photons n:

4. In one minute, a monochromatic bulb gives out a million photons of frequency 600 THz. What is the power of the bulb?

First calculate the energy carried by one photon:

Then work out the energy carried by 1,000,000 photons:

Then work out the power of the bulb:

...maybe its a nanobulb.

5. The photons in a beam of electromagnetic radiation carry 2.5μJ of energy each. How long should the phasors representing this radiation take to rotate?

First calculate the frequency of each photon:

(That's one nasty gamma ray.)

Then calculate the time taken for one 'wavelength' to go by: