### Natural Science

Understanding Colour

Questions:

1. Sketch an appropriate spectral curve for each of t he following objects, remembering to clearly label the
axes with titles and units in the provided graph space.

a) blue star b) yellow i ncandescent light bulb

0
100
200
300
400
500
600
20 21 22 23 24 25 26 27 28 29 30

0
100
200
300
400
500
600
20 21 22 23 24 25 26 27 28 29 30

c) green chalk board d) red sta ge filter light

0
100
200
300
400
500
600
20 21 22 23 24 25 26 27 28 29 30

0
100
200
300
400
500
600
20 21 22 23 24 25 26 27 28 29 30

2. a) What is a key physical difference between the spectral curves in 1 (a) and (b) versus (c) and (d )?

b) How do we show this difference in the spectral curves?

3. a) Sketch two different types of spectral curves to represent the same green dress, clearly labelin g axes
with titles and units.

0
100
200
300
400
500
600
20 21 22 23 24 25 26 27 28 29 30

0
100
200
300
400
500
600
20 21 22 23 24 25 26 27 28 29 30

b) Explain why the two curves you sketched in 3 a) are equivalent for this green dress.

PART B : Light-as-a-Wave Phenomena

4. Consider the following 4 cases of light travelin g from one medium into another. There are three med ia
involved in these cases: air (n=1.0003), water (n=1 .3), and glass (n=1.5). One of the two media is alw ays air
(meaning the other medium is either water or glass) . Label each case with the appropriate medium name
and index of refraction (for each medium 1 and 2), on each diagram.

7. a) Explain the difference, if any, between refra ction and dispersion of white light. Use diagrams to help

b) Explain the difference, if any, between refraction and dispersion of red light. Use diagrams to help

c) Using the same prism in your diagram, expla in the difference in refraction of red and blue light.

rstanding Colour
8. a) How can a total internal reflection of light happen?

b) Consider the following 3 media: air (n=1.0003), water (n=1.333), glass (n=1.5). Consider also the
critical angle values for the following medium-interfaces: water-air (! c = 42°), glass-air (! c =49°), glass-water ( ! c =63°). Sketch three separate examples where

total i nternal reflection of light can happen, using
only the three media listed above. Make sure to pro perly label all your diagrams.

9. a) Sketch the interference wave, in the blank g raph
space, of the two original interfering waves. Make sure
to properly label the y-axis, and to have at least 20 data
points on your graph (roughly 2 per each ‘square box’
along the x-axis).

b) How did you determine the resultant wave?

NATS 1870B: Understanding Colour Assignment 2: Light Part 2
F-W 2014-15

Page 6 of 6
10. Consider the thin-film interference principles as seen in soap bubbles. Sketch and label, at the c orrect
locations in the soap bubble below, the paths of incoming white light and outgoing red and blue light waves
that would interfere to produce the cyan and yellow colours as viewed by the eye.

11. Explain the reasoning for where you drew the in terfering red and blue waves.