Chapter 8: Light

Question 1

What is a convergent ray?

Answer 1

A beam of light where the light rays converge onto a point

Question 2

What is a divergent ray?

Answer 2

A beam of light where the light rays originate from a point and spread out

Question 3

Where does the incident ray, reflected ray and normal meet at?

Answer 3

The point of incidence

Question 4

How is the angle of incidence related to the angle of relfection?

Answer 4

They are equal to each other

Question 5

What are the characteristics of a plane mirror image?

Answer 5

The image is the same size as the object, the image is laterally inverted, the image is upright, the image is virtual, the distance of the image from the mirror is equal to the distance of the object from the mirror

Question 6

Why does light refract?

Answer 6

Light travells at different speeds in different mediums. When light travells from one medium to another, it will change speed at the boundary of the two media, which causes light to bend

Question 7

Which ray undergoes a change in direction?

Answer 7

The refracted ray

Question 8

When light enters a denser medium, what happens?

Answer 8

Light slows down, and the refracted ray bends towards the normal

Question 9

When light enters a less dense medium, what happens?

Answer 9

Light speeds up, and refracted ray bends away from the normal

Question 10

What happens to the light ray when it enters a medium parallel to the normal?

Answer 10

There is no refraction

Question 11

How can the refractive index be found using the speed of light in a medium?

Answer 11

refractive index (n) = speed of light in vacuum (c) / speed of light in medium (v)

Question 12

How can the refractive index be found using the ray of incidence, ray of refraction, and one of the refractive indexes of a medium?

Answer 12

refractive index i (ni) x sin i = refractive index r (nr) x sin r

Question 13

How can the refractive index be found using real and apparent depth of an object?

Answer 13

refractive index (n) = real depth / apparent depth

Question 14

How can the critical angle of an object be found?

Answer 14

sin critical angle (c) = 1 / refractive index (n)

Question 15

What happens when the angle of incidence is less than the critical angle of an object?

Answer 15

Light is refracted, a small amount of light is reflected

Question 16

What happens when the angle of incidence is equal to the critical angle of an object?

Answer 16

The emergent ray is perpendicular to the normal, and the refracted ray travells along the plane of the surface of the object

Question 17

What happens when the angle of incidence is more than the critical angle of an object?

Answer 17

Total internal reflection occurs, no light passes through the point of incidence, and is only reflected within the object

Question 18

What is meant by the critical angle

Answer 18

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 19

What are the two conditions for total internal reflection to take place?

Answer 19

The light ray must originate from a optically denser medium, and the angle of incidence must be greater than the critical angle

Question 20

What is a lens?

Answer 20

A transparent optical medium, made of glass or plastic, which has a curved surface

Question 21

Why does a beam of light refract as it enters a lens?

Answer 21

As the upper and lower surface of a lens is curved, light rays on the surface of the lens experience different incidence angles, and this causes the light rays to refract. The speed of light also slows down when entering a lens as it is an optically denser medium

Question 22

Why are distant objects used to determine the focal point of a lens?

Answer 22

The light rays entering the lens has to be parallel to each other for the image formed to be clear and sharp. Therefore, and object needs to be far away to ensure the light rays will be parallel

Question 23

What is the focal length of a lens?

Answer 23

The distance between the lens and the screen where the image of the object is formed

Question 24

What is the focal point of a lens?

Answer 24

The point where all of the light rays that pass through a lens converge

Question 25

What equation relates the distance of the object from the lens, the distance of the image from the lens, and the focal length?

Answer 25

1 / distance of object from the lens (u) + 1 / distance of image from the lens (v) = 1 / focal length (f)

Question 26

How can the focal length be found if the object is far away?

Answer 26

Since 1 / distance of object from lens (u) is negligable, distance of image from lens (v) = focal length (f)

Question 27

What is a real image?

Answer 27

A real image is formed when light actually converges and forms on a screen, and happens when the object is placed outside the focal length

Question 28

What is a virtual image?

Answer 28

A virtual image is formed when light appears to have converged, and when the object is placed within the focal length

Question 29

How can the linear magnification of an image be found?

Answer 29

Linear magnificiation = Distance of image from lens / Distance of object from lens = Image height / Object height

Question 30

What type of image is formed when the distance of object from the lens is less than or equal to the focal length?

Answer 30

A virtual, upright and magnified image

Question 31

What type of image is formed when the distance of object from the lens is more than the focal length, but less than twice the focal length?

Answer 31

A real, inverted and magnified image

Question 32

What type of image is formed when the distance of object is equal to twice the focal length?

Answer 32

A real and inverted image

Question 33

What type of image is formed when the distance of object is more than twice the focal length?

Answer 33

A real, inverted and diminisihed image