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

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

**2. A photon carries 10 ^{-30}J 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: