Lecture 6 - What is Colour

Question 1

What is colour

Answer 1

Wavelength of light

Question 2

What is wavelength

Answer 2

distance between 2 peaks on same wave

Question 3

What is frequency

Answer 3

the number of complete waves generated per second

Question 4

What is period

Answer 4

How long a wave takes to go through the full range of motion

Question 5

What is light characterised by

Answer 5

Light is characterised by its wavelength or its frequency

Question 6

Colour temperature

Answer 6

• Thermal sources of light emit radiant energy in proportion to their temperature - commonly observed when piece of metal is heated

Question 7

What happens when a piece of metal is heated

Answer 7

It changes colour

Question 8

What colour does the metal glow when temperature increases and how

Answer 8

Red

Emit light - radiant energy - heat - glows red

Question 9

What colour is very hot

Answer 9

Blue

Question 10

What is a blackbody radiator

Answer 10

Perfect blackbody - theoretical object ( not exist in reality )

Question 11

What does a blackbody radiator do

Answer 11

ABSORB all radiation that falls on it - it would not reflect or transmit any radiation
Best emitter of radiation

Question 12

Does a blackbody radiator absorb or reflect

Answer 12

Absorb

Question 13

What is an example of a blackbody radiator and why

Answer 13

Stars
Blackholes
Good at absorbing all wavelenghts, but not perfect

Question 14

What is property of something that is NOT a blackbody radiator

Answer 14

• White/shiny silver surfaces
• Worst absorbers
• Poor emitters
• Best reflecters

Question 15

Example of something that is NOT a blackbody radiator and why

Answer 15

Radiators

Painted white - infrared radiation is emitted gradually - poorly - emit heat slowly

Question 16

Link between temperature and wavelength

Answer 16

Increase in temp = shorter wavelengths

As temp increases, there’s a shift in wavelengths emitted

Question 17

What is the shorter wavelength

Answer 17

Blue

Question 18

What can a blackbody be specified by

Answer 18

Its colour temperature

Question 19

What source is at a temp of 3000K

Answer 19

Warm white compact fluorescent and LED lamps

Question 20

What source is at a temp of 5000K

Answer 20

Cool white fluorescent lamps ( hotter temp but cooler )

Question 21

Colour temp and sensation link

Answer 21

Higher colour temp ( warmer ) - colder sensation

Question 22

What is CIE ( x,y) Colour Space

Answer 22

Specifies colours graphically using x,y co-ordinates

Question 23

If its closer to centre is it more or less saturated and what is the colour

Answer 23

Closer to centre - less saturated - white

Question 24

If its further from edges ( chart ) it more or less saturated

Answer 24

More saturated

Question 25

The co - ordinates x,y map the colour with respect to what

Answer 25

Hue and saturation

Question 26

What are the spectral colours

Answer 26

Correlated to a specific wavelength

Question 27

Where is the lines of purples located

Answer 27

Along bottom

Question 28

How can achromatic colour also be achieved

Answer 28

With many different mixtures of light

Question 29

What is additive colour mixing

Answer 29

- Mixing of light - Superposition of RED, GREEN and BLUE lights - Almost all visible colours can be obtained by additive colour mixing of 3 colours - Involves primary colours

Question 30

What is cyan

Answer 30

Red

Question 31

What is magenta

Answer 31

Green

Question 32

What is tello

Answer 32

Blue

Question 33

Where is additive colour mixing used

Answer 33

Computer monitors

Question 34

What are the 3 primary colours and what colour do they produce when mixed

Answer 34

Red, green, blue | Produce white

Question 35

What is subtractive colour mixing

Answer 35

Colours created by partially/completely subtracting ( absorbing ) some wavelengths of light and not others

Question 36

Where is subtractive colour mixing used

Answer 36

Coloured pigments, dyes, paints, inks

Question 37

In colour printing what are usually the primary colours

Answer 37

Cyan, Magenta, Yellow and Black