Chapter 10: Light

Question 1

Types of light rays

Answer 1

Parallel
Convergent
Divergent

Question 2

First law of reflection

Answer 2

The first law of reflection states that the incident ray, reflected ray and the normal at the point of incidence all lie in the same plane

Question 3

Second law of reflection

Answer 3

The second law of reflection states that the angle of incidence is equal to the angle of reflection (i = r)

Question 4

Reflection

Answer 4

The rebounding of light at a surface

Question 5

Incident ray

Answer 5

Light ray that hits the reflecting surface

Question 6

Point of incidence

Answer 6

The point at which the incident ray hits the reflecting surface

Question 7

Normal

Answer 7

The perpendicular to the reflecting surface at the point of incidence

Question 8

Reflected ray

Answer 8

Light ray that bounces off the reflecting surface

Question 9

Angle of incidence

Answer 9

The angle between the incident ray and the normal

Question 10

Angle of reflection

Answer 10

The angle between the reflected ray and the normal

Question 11

Types of reflection

Answer 11

Regular
Diffuse (irregular)

Question 12

Characteristics of regular reflection

Answer 12

Occurs at smooth surfaces eg mirrors

The law of reflection holds true for each individual ray: angle of incidence = angle of reflection

Parallel incident rays are reflected in the same direction as the surface is smooth. All rays have the same angles of incidence and reflection

The normal at all points of incidence are parallel to one another

Question 13

Characteristics of diffuse reflection

Answer 13

Occurs at rough surfaces eg cloth

The law of reflection holds true for each individual ray: angle of incidence = angle of reflection

Parallel incident rays are reflected in different directions because the surface is uneven. The angles of incidence and reflection of one ray are different from those of another ray

The normal at all points of incidence are not parallel to one another

Question 14

Characteristics of a plane mirror image

Answer 14

The image is of the same size as the object

Laterally inverted

Upright

Virtual

Its distance from the mirror is equal to the distance of the object from the mirror

Question 15

Applications of mirrors

Answer 15

Vision testing

Blind corner mirror

Periscope

Question 16

Refracted ray

Answer 16

Light ray that enters a medium and undergoes a change of direction

Question 17

Refraction

Answer 17

The bending of light as light passes from one optical medium to another

Question 18

First law of refraction

Answer 18

The first law of refraction states that the incident ray, refracted ray and the normal all lie in the same plane

Question 19

Second law of refraction (Snell’s Law)

Answer 19

The second law of refraction states that, for two given media, the ratio of the sine to the angle of incidence to the sine of the angle of refraction is a constant

sin i / sin r = constant

Question 20

Refractive index of a medium

Answer 20

The ratio of the speed of light in vacuum to the speed of light in the medium
n = c / v
n = sin i / sin r

Question 21

Critical angle

Answer 21

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

Question 22

Total internal reflection

Answer 22

the complete reflection of a light ray inside an optically denser medium at its boundary with an optically less dense medium

conditions:
1. the light ray in an optically denser medium strikes its boundary with an optically less dense medium
2. the angle of incidence is greater than the critical angle of the optically denser medium

applications:
binoculars
periscopes
single lens reflex (SLR) cameras

Question 23

Focal length

Answer 23

the distance between the optical centre and the focal point