OP - How is Light Produced? - Week 1

Question 1

At what temperature do objects begin to emit visible light?

Answer 1

1.5K

Question 2

Name the two categories of light production.

Answer 2

Incandescence

Luminescence

Question 3

Define colour temperature.

Answer 3

Temperature at which a black body at the corresponding temperature would emit that wavelength.

Question 4

Define black body. Why is it named so?

Answer 4

The ideal incandescent source is called a black body. It is called a black body because the ideal incandescent source must also be a perfect absorber. The perfect absorber must be black.

Question 5

Describe Wein’s displacement law.

Answer 5

Peak wavelength decreases with temperature.

Question 6

Describe Planck’s law.

Answer 6

Extended Wien’s law to short wavelengths and gave the shape of the intensity versus wavelength curve for different colour temperatures.

Question 7

Describe Stefan-Boltzmann’s law.

Answer 7

Total amount of radiation emitted varies as the fourth power of the temperature.
σT^4

Question 8

How do real sources of incandescence differ from black bodies?

Answer 8

They always emit less radiation than the black body at the same temperature, because real bodies are grey, not black.

Question 9

Define luminescence.

Answer 9

Production of light by non-thermal or non-incandescent means.

Question 10

Name 4 types of luminescence.

Answer 10

Fluorescence
Phosphorescence
Chemi-luminescence

Question 11

Define electro-luminescence. Name examples.

Answer 11

Luminescence caused by electrical 
activity.
Gas lamps
Gas lasers
Solid states, LEDs, diodes

Question 12

How does electro-luminescence work? Name 2 ways.

Answer 12

Ionised gas can reassemble releasing light.
Atoms struck by electrons can have their electrons move up a shell. When they return to ground state, they release light.

Question 13

How do LEDs work?

Answer 13

Has 2 parts, n-type and p-type.
n-type is negatively charged with a lot of electrons.
p-type is positive, and has few electrons.
When a voltage is applied, a current flow is induced, and electrons meeting the deficiency results in the release of light.

Question 14

Describe the reaction used by the firefly to produce bioluminescence.

Answer 14

luciferin + luciferase + ATP + oxygen = excited product + luciferase + light

Question 15

Describe the difference between fluorescence and luminescence.

Answer 15

Luminescence - generation of light via a chemical reaction.

Fluorescence - absoprtion of light at one wavelength, and re-emission at another