3ab. Reflection & Refraction of Light

Question 1

Incident Ray

Definition

Answer 1

The light ray going towards the surface.

Question 2

Reflected Ray

Definition

Answer 2

The light ray going away from the surface.

Question 3

Point of Incidence

Definition

Answer 3

The point at which the incident ray strikes the surface.

Question 4

Normal

Definition

Answer 4

The perpendicular line to the surface at the point of incidence.

Question 5

Angle of Incidence

Definition

Answer 5

The angle between the incident ray and the normal.

Question 6

Angle of Reflection

Definition

Answer 6

The angle between the reflected ray and the normal.

Question 7

2 Laws of Reflection

Answer 7

1. The incident ray, reflected ray and the normal at the point of incidence lie in the same plane.
2. The angle of incidence is equal to the angle of reflection. ∠i = ∠r

Question 8

Regular Reflection

Where it occurs + Characteristics

Answer 8

Occurs at smooth surfaces.

As the surface is smooth, the parallel incident rays are reflected in the same direction and the reflected rays remain parallel to each other.

All the rays have the same angles of incidence and reflection.

The laws of reflection apply for each individual ray.

Question 9

Diffused Reflection

Where it occurs + Characteristics

Answer 9

Occurs at rough surfaces.

As the surface is uneven/rough, the parallel incident rays are reflected in different directions.

The normal at different points on the surface are not parallel to one another.
Angles of incidence and reflection of one ray are different from that of the other rays.

The laws of reflection apply for each individual ray.

Question 10

Characteristics of an image formed in a plane mirror

Answer 10

1. The image is of the same size as the object.
2. The image is upright.
3. The image is virtual (cannot be projected or captured onto a screen).
4. The image is laterally inverted.
5. The distance of the image from the mirror is the distance of the object from the mirror (perpendicular image distance = perpendicular object distance).

Question 11

Refraction

Definition

Answer 11

Refraction is the bending of light as it passes from one medium to another medium of different optical density.

Question 12

Refracted Ray

Definition

Answer 12

The light ray that enters a medium and undergoes a change of direction.

Question 13

Angle of Refraction

Answer 13

The angle between the refracted ray and the normal.

Question 14

Why and how does refraction occur?

Answer 14

When light travels from optically less dense to optically denser medium, the speed of light decreases and light bends towards the normal. i > r

When light travels from optically denser to optically less dense medium, the speed of light increases and light bends away from the normal. i < r

Question 15

Refractive Index

Definition + Formula + Relationship with speed of light

Answer 15

Refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in the medium.
n = c/v
n: refractive index
c: speed of light in vacuum, 3.0 x 10⁸
v: speed of light in medium

The larger the refractive index, the lower the speed of light and the larger the bending of light.

Question 16

2 Laws of refraction

Answer 16

1. The incident ray, refracted ray and the normal at the point of incidence all lie in the same plane.
2. For two given media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. (Snell’s Law, sin i/sin r = constant)

Question 17

Total Internal Reflection

Definition + 2 Conditions

Answer 17

Total internal reflection is the complete reflection of a light ray in an optically denser medium at the boundary with an optically less dense medium.

2 Conditions:

1. Light travels from an optically denser to an optically less dense medium
2. Angle of incidence in the optically denser medium is larger than the critical angle

Question 18

Critical Angle

Definition

Answer 18

Critical angle is the angle of incidence in an optically denser medium for which the angle of refraction in the optically less dense medium is 90°

Question 19

What happens when ∠i is increasing but is…

Less than ∠c + Equal to ∠c + Greater than ∠c

Answer 19

When ∠i is than ∠c:

1. Refraction takes place
2. ∠r increases from 0° to 90°
3. Presence of weak internally reflected ray

When ∠i is equal to ∠c:

1. ∠r equals to 90°
2. Presence of weak internally reflected ray

When ∠i is greater than ∠c:

1. Total internal reflection occurs
2. No refracted ray

Question 20

Why are glass prisms better light reflectors than mirrors

Answer 20

Glass prisms are used to reflect light by total internal reflection in optical instruments (binoculars, periscopes).

Better light refectors than mirros because they:

1. Do not produce multiple reflections
2. Do not have a silvered surface that can wear off

Question 21

5 advantages of using optical fibres over copper wires in telecommunications

Answer 21

1. Data transfer rate is faster
2. Less signal Loss
3. Lighter and cheaper
4. Can carry much more information over long distances
5. Immune to electromagnetic interference

Question 22

2 advantages of using optical fibres in medicine

Answer 22

Used in endoscopes

1. Thin and light (minimally invasive)
2. Flexible (can curve around obstacles in body)