1.3 Photons

EM wave properties

• consists of an electric wave and a magnetic wave

• These waves travel together and vibrate at right angles to each other to the direction which they are travelling

• In phase with each other

When are EM waves emitted?

When a charged particles loses energy. This can happen when:

• a fast moving electron is stopped or slows down or changes direction

• An electron in a shell of an atom moves to a different shell of lower energy

What are EM waves emitted by?

Charged particles

What are EM waves emitted as?

Short bursts of waves, where each burst leaves the source in a different direction.

Each burst is a packet of EM waves and is referred to as a PHOTON

What is a photon?

A packet of electromagnetic energy

What does the energy of a photon depend on and what is the equation to support this?

The energy of a photon depends on its frequency

Energy = Planck’s constant * frequency

Energy = (Planck’s constant * speed of light) / wavelength

What does a laser beam consist of?

Photons of the same frequency

What is the power of a laser beam equal to?

The energy per second transferred by the photons

Power of the beam = nhf

Explain the equation

Laser power = nhf

Power is equivalent to energy over time

In the equation power = nhf, hf is equivalent to the energy of a photon.

n = the number of photons in the beam passing a fixed point per second

Therefore, if n photons pass a fixed point each second, the energy per second is nhf.