PHY 11 - Light and Geometrical Optics

Question 1

What is the approximate speed of light in a vacuum ?

Answer 1

295 000 000 m/s

Question 2

What is refraction of light dependent on ?

Answer 2

The density of the medium

e.g. water = low density and therefore minimum refraction

Question 3

What is meant by the rarer medium in terms of light ?

Answer 3

The least dense medium

Question 4

What happens to light when it passes from a rarer to a denser medium ?

Answer 4

It is refracted towards the normal (90º to the surface)

Question 5

What happens to light when it passes from a denser to a rarer medium ?

Answer 5

It is refracted away from the normal (90º to the surface)

Question 6

What is the difference between the angle of incidence and the angle of refraction ?

Answer 6

They are equal

Question 7

Why do we see colour ?

Answer 7

Different wavelengths of light make up the visible portion of the light spectrum (the electro-magnetic spectrum)

Question 8

Describe the two aspects of the theory of light

Answer 8

1. Particulate - referring to a packet of energy called a photon e.g. used to describe the photoelectric effect
2. Wavy - e.g. light interference and diffraction

Question 9

Why does diffraction occur ?

Answer 9

When waves of light bend at the interface between two different media.

Question 10

Describe the optical domain of the electromagnetic wave theory ?

Answer 10

It corresponds to the following range of wavelengths:

0.4µ< h (visible) < 0.8µ

(µ = microns = 10^-6 metres)

Question 11

What is an electromagnetic field ?

Answer 11

At every point of the field there are two perpendicular vectors:

E: Electrical field vector

B: Magnetic induction field vector

Question 12

What is polarized light ?

Answer 12

The electromagnetic wave front is polarized in a straight line when E and B are fixed at all times.

Therefore, it is light that has waves in only 1 plane.

Question 13

What is reflection in terms of light ?

Answer 13

The process by which light rays bounce back into a medium from a surface with another medium.

Question 14

What is the difference between an incident and a refracted ray ?

Answer 14

The ray that arrives from the source is the incident ray, the reflected ray is the ray that bounces back

Question 15

What are the laws of reflection ?

Answer 15

The angle of incidence equals the angle of reflection at normal.

Question 16

What are spherical mirrors ?

Answer 16

They are non-plane mirrors which may have the reflecting surface concave (converges light) or convex (diverges light)

Question 17

What is a vertex ?

Answer 17

The centre of a mirror

Question 18

Describe the convention for lower and upper case letters in terms of light optics

Answer 18

Upper case: refer to a point

Lower case: refer to a distance

Question 19

What is refraction ?

Answer 19

The bending of light as it passes from one transparent medium to another. This is caused by the different speeds of light in the two media

Question 20

What is the relationship between wavelength and speed ?

Answer 20

Longer wavelengths travel faster in a medium than shorter wavelengths (ie. longer wavelengths are more subject to refraction)

Question 21

What is dispersion of light ?

Answer 21

The separation of white light (ie. all colours together) into individual colours by differential refraction

Question 22

What are the laws of refraction ?

Answer 22

1. The incident ray, the refracted ray and the normal ray all lie in the same plane
2. The path of the ray (incident and refracted parts) is reversible

Question 23

What is the critical angle in terms of light optics ?

Answer 23

Question 24

Explain why when looking at an object under water from above the surface, the object appears closer than it actually is ?

Answer 24

Question 25

What is a lens ?

Answer 25

A transparent material which refracts light

Question 26

What is the difference between converging and diverging lenses ?

Answer 26

Converging lenses refract toward the axis, diverging lenses refract away from the axis.

Question 27

What are aberrations in terms of light optics ?

Answer 27

E.g. A nick or a cut in a convex lens might create a microscopic are of concavity, causing divergent light instead of convergent light. The image will be less sharp or clear as the number or sizes of aberrations increase.