Light

Question 1

What are the laws of reflection?

Answer 1

1. The angle of incidence equals the angles of reflection
2. The incident ray, reflected ray and normal all lie in the same plane

Question 2

What are the five properties of a image formed by a plane mirror?

Answer 2

1. Same size
2. Upright
3. Virtual
4. Laterally inverted
5. Same distance behind the mirror as the object in front

Question 3

What is a real image?

Answer 3

An image which can be projected onto a screen

Question 4

What is a virtual image?

Answer 4

An image which cannot be projected onto a screen

Question 5

Diagram of reflection on a plane mirror?

Answer 5

Look in Book

Question 5

Diagram of reflection on a periscope?

Answer 5

Look in Book

Question 6

Diagram of reflection of light for image formation?

Answer 6

Look in Book

Question 7

What is refraction?

Answer 7

The bending of light due to its change in speed after moving from one medium to another with a different refractive index.

Question 8

What are the requirements for refraction?

Answer 8

1 – Ray passes from one medium into another with a different refractive index.

2 – At an angle of incidence > 0 degrees.

Question 9

What are examples of refraction?

Answer 9

• Glasses
• Eyes
• Telescope
• Magnifying Glass

Question 10

Does all light pass through when it is refracted?

Answer 10

When light passes from one medium, say air, to another, say glass, part is reflected back into the first medium ( 4% ) and the rest passes into the second medium with its direction changed.

Question 11

Diagram of refraction through a water drop?

Answer 11

Look in Book

Question 12

Diagram of refraction through a glass block?

Answer 12

Look in Book

Question 13

What changes in the light when it enters the glass from air?

Answer 13

Speed - Decreases
Wavelength - Decreases
Frequency - Constant

Question 13

What changes in the light when it exits glass into air?

Answer 13

Speed - Increases
Wavelength - Increases
Frequency - Constant

Question 14

Why does certain colours of light refract less or more?

Answer 14

The amount of refraction that takes place depends on the change of speed in light.

Violet light refracts more as it experiences a greater change of speed than red light

Question 15

What is dispersion?

Answer 15

When white light passes through an new medium the different colours of light are refracted by different amounts.

Red light slows down the least and refracts the least
Violet light slows down the most and refracts the most

Question 16

What is the critical angle?

Answer 16

The critical angle is the (limiting) angle of incidence which gives an angle of reflection of 90 degrees

Question 16

What two conditions are necessary for total internal reflection?

Answer 16

1. The angle of incidence is greater than the critical angle
2. The ray must be incident from a higher refractive index medium to a lower refractive index medium

Question 17

How does total internal reflection take place when the angle of incidence is less than the critical angle

Answer 17

Refracts as normal with 4% reflecting internally

Question 17

How does total internal reflection take place when the angle of incidence is equal to the critical angle

Answer 17

Refracts at a 90 degree angle with 4% reflecting internally

Question 18

How does total internal reflection take place when the angle of incidence is greater than the critical angle

Answer 18

Does not refract and reflects 100% internally

Question 19

Explain how optical fibre cables satisfy TIR?

Answer 19

Their core has a very high refractive index and the cladding that surrounds their core has a very low refractive index. Meaning as long as I > C, TIR takes place

Question 20

What are non-medical uses of optical fibre?

Answer 20

Long distance communication as they allow transfer of large quantities of data along the cable at high speeds over large distances.

Bomb Disposal

FBI - Surveillance

Borescope - Used by engineers to inspect aircraft engines, gas turbines, steam turbines and diesel engines etc

Question 21

How is optical fibre used in the medical industry?

Answer 21

An endoscope is an instrument that allows images from inside a person body to be seen by a physician.

They use fibre optic cables to deliver non-coherent light into the body and take coherent light from the body back to an eyepiece to form a clear image

Question 22

What is meant by coherent cables?

Answer 22

The fibre going from the body or object to the eye or computers needs to be coherently

They have the same spatial relationship

Question 23

What are the properties of a converging lens?

Answer 23

• Thicker at the centre
• Thinner at its edges
• Serves to converge light

Question 24

What are the properties of a diverging lens?

Answer 24

• Thinner at the centre
• Thicker at its edges
• Serves to diverge light

Question 25

What is a lens?

Answer 25

A carefully ground or moulded piece of transparent material which refracts light to form an image

Question 26

What are other names for converging lenses?

Answer 26

Biconvex and Convex

Question 27

What are other names for converging lenses?

Answer 27

Biconcave and Concave

Question 28

All does light converge on the focal point of a converging lens?

Answer 28

All rays parallel to the principal axis, converge and pass through the focal point of the lens

Question 29

All does light rays diverge on the focal point of a diverging lens?

Answer 29

All rays travelling parallel to the principal axis appear to diverge from the focal point.

Question 30

How do you find the focal length of a converging lens?

Answer 30

The focal length of a converging lens is the distance from the optical centre to the focal point.

Look in book for diagram which explains this well

Question 31

What is the method for using a distant object to find the focal length of a converging lens.

Answer 31

1. Locate a distant object and place a metre stick in the objects direction
2. Place a convex lens mounted on a lens stand at the 5cm mark
3. Place a white screen behind the lens in line with the scale
4. Move the screen backwards and forwards until a sharp, inverted and diminished image forms of the distant object.
5. Record the screen and lenses positions, the difference between them is equal to the focal length of the convex lens.
6. Repeat the experiment a few times and take an average for accuracy and reliability

Question 32

Diagram for a converging lens?

Answer 32

Look in Book

Question 32

Diagram for a converging lens?

Answer 32

Look in Book

Question 33

Diagram for diverging lens for forming an image?

Properties of that image?

Answer 33

Look in Book

Diminished, Upright, Virtual

Question 34

Diagram for converging lens for forming an image?

(When the object is behind 2F)

Properties of that image?
Examples?

Answer 34

Look in Book

Inverted, Diminished, Real

Examples: Eyes and Cameras

Question 35

Diagram for converging lens for forming an image?

(When the object is between 2F and F)

Properties of that image?
Examples?

Answer 35

Look in Book

Magnified, Inverted, Real

Examples: Projector

Question 36

Diagram for converging lens for forming an image?

(When the object is on the focal point)

Properties of that image?
Examples?

Answer 36

Look in book

The object is formed at infinity and parallel rays

Question 36

Diagram for converging lens for forming an image?

(When the object is in front of the focal point)

Properties of that image?
Examples?

Answer 36

Look in Book

Magnified, virtual, Upright

Examples: Magnifying Glass

Question 37

What is a luminous and non-luminous object?

Answer 37

A luminous object is an entity that produces its own light, either naturally or artificially.

Non-luminous objects, on the other hand, do not produce their own light and can only reflect light from external sources.