Stuff

Question 1

Define light.

Answer 1

Light is an electromagnetic wave within a certain portion of the electromagnetic spectrum.

Question 2

What is the electromagnetic spectrum?

Answer 2

The classification of electromagnetic waves by energy.

Question 3

What are the different categories of the electromagnetic spectrum, in order of increasing energy?

Answer 3

radio waves
microwaves
infrared light
visible light
ultraviolet light
X-rays
gamma rays

Question 4

What are the colours associated with visible light, in order of increasing energy?

Answer 4

red
orange
yellow
green
blue
indigo
violet

Question 5

White ______ light is composed of a _______ _______ of colours.

Answer 5

visible | continuous sequence

Question 6

Compare luminous and non-luminous sources.

Answer 6

Luminous sources produce their own light. Non-luminous sources do not.

Question 7

Give three examples of luminous sources.

Answer 7

The Sun, a light bulb, a lit match, a flashlight…

Question 8

Give three examples of non-luminous sources.

How are non-luminous sources seen?

Answer 8

Tree, textbook, pencil, bicycle…

They can only be seeing by using reflected light

Question 9

What is incandescence?

Answer 9

When light is produced resulting from high temperature

Question 10

Give three examples of incandescence.

Answer 10

light from candle
light from a stove’s burner
incandescent light bulb

Question 11

What is electric discharge?

Answer 11

When light is produced by passing electric current through a gas.

Question 12

Give two examples of electric discharge.

Answer 12

lightning

neon signs

Question 13

What is phosphorescence

Answer 13

When visible light is produced from the absorption of ultraviolet light. This results in the emission of visible light over an extended period of time.

Question 14

How do glow-in-the-dark objects glow?

Answer 14

They are coated with phosphors which undergo phosphorescence. When they absorb UV light, they keep some of the energy and release lower-energy visible light.

Question 15

What is fluorescence?

Answer 15

When visible light is emitted immediately resulting from the absorption of ultraviolet light.

Question 16

Where is fluorescence used in products?

Answer 16

fluorescent dye in highlighter pens, as well as in laundry detergent to make clothing glow
compact fluorescent lights (CFLs)

Question 17

Fluorescent lights make use of both _____ _____ and ______

Answer 17

electric discharge | flourescence

Question 18

What is chemiluminescence?

Answer 18

When light is produced directly from a chemical reaction with little or no heat produced.

Question 19

Where is chemiluminescence used?

Answer 19

Light sticks

Question 20

What is bioluminescence?

Answer 20

When light is produced in living organisms from a chemical reaction with little or no heat produced.

Question 21

Where is bioluminescence found? Give three examples.

Answer 21

Fireflies, glow-worms, some fish

Question 22

Why do living organisms use bioluminescence?

Answer 22

To protect themselves from predators and attract mates.

Question 23

What are some properties of light?

Answer 23

It is the fastest thing ever observed to move
Reflects off surfaces
Refracts when moving from one medium to another
Travels in straight lines

Question 24

What is the difference between specular and diffuse reflection?

Answer 24

Specular reflection is when light reflects off a smooth surface. Angles of incidence and reflection will be the same for all rays hitting the surface.

Diffuse reflection is when light reflects off an irregular or dull surface. Angles of incidence and reflection will be different for the rays. The image will be fuzzy and/or warped.

Question 25

Explain apparent depth.

Answer 25

When an object is submerged in a transparent medium like water, the light coming from it will refract away from the normal as it exits the water into less optically dense air. When the eye sees the refracted ray, the brain extrapolates the ray backwards in a straight line which creates a virtual image in the water. The resulting image is higher than the actual object.

Question 26

What are the conditions for total internal reflection to happen? What actually happens?

Answer 26

Light must travel more slowly through the first medium than the second (refracts away from normal)

The angle of incidence is larger than the critical angle.

No refraction occurs in the second medium and instead the ray is reflected back into the first medium.

Question 27

Why do lasers emit light of a very pure colour?

Why is laser light so intense?

Answer 27

It produces electromagnetic waves of the same energy level throughout.

The electromagnetic waves travel in exactly the same direction, concentrated in one narrow beam.

Question 28

What is refraction?

Answer 28

When light bends when it travels from one medium to another.

Question 29

What is the index of refraction?

Answer 29

The ratio of the speed of light in a vacuum to the speed of light in a medium.

n=c/v
n=sin(angle of incidence)/sin(angle of refraction)

Question 30

What are two applications of total internal reflection?

Answer 30

Diamonds have a very high index of refraction, and thus a very small critical angle. This means that a lot of light undergoes internal reflection inside the diamond. This causes a sparkling effect when the light exits the top of the diamond.

Triangular prisms are much more useful for reflecting light than mirrors because they reflect almost 100% with total internal reflection. Mirrors, on the other hand, lose some light through absorption. This is why optical devices such as cameras and binoculars use prisms instead of mirrors.