Quantum - Electromagnetic Waves

Question 1

The electromagnetic Spectrum

Answer 1

• The electromagnetic spectrum is the range of all possible frequencies of radiation
• the spectrum is often split into the high and low-frequency regions, compared with visible light.
• The higher frequency region includes ultraviolet, X-rays and gamma rays. These are all ionising forms of radiation.
• The low-frequency region of the spectrum includes infrared, microwaves and radio waves.
• The frequencies of the different points are: Gamma rays = f > 10^19 Hz
X-rays = 10^16 Hz < f < 10^19 Hz
Ultra Violet = 8 * 10^14 Hz < f < 10^16 Hz
Visible Light = 4 * 10^14 Hz < f < 8 * 10^14 Hz
Infrared = 10^11 Hz < f < 4 * 10^14 Hz
Microwaves = 10^9 Hz < f < 10^11 Hz
Radio Waves = f < 10^9 Hz

Question 2

Photons

Answer 2

• In quantum Physics, light can be viewed as having a particle-like nature.
• The energy of light can be carried in discrete packets or particles, called photons.
• The energy of a photon of light is linked to the frequency of the light by the equation E = hf

Question 3

Continuous absorption and emission spectra

Answer 3

• If a continuous spectrum of light, containing all wavelengths within a range, is passed through gas like hydrogen, dark lines will appear in the spectrum. This is because the electrons in the gas have discrete energy levels.
• If a photon of the right energy, corresponding to the energy gap between a level containing an electron and a higher, empty level hits the atom, it will promote the electron to a higher energy level. This electron will drop down into the initial energy level, re-emitting a photon of the same energy but in a random direction.
• As the energy of a photon is linked to the frequency of light by the equation E=hf this means that for frequencies corresponding to the energy gap, this light will be absorbed and then emitted in a random direction. Only a small amount of light from these frequencies will be emitted in the direction of the detector, causing the “absorption” lines.

Question 4

Speed of electromagnetic waves

Answer 4

• The speed of electromagnetic waves, and the light, is determined by the way in which a material responds to electric and magnetic fields