Optics

Question 1

What is light ?

Answer 1

An electromagnetic wave consisting of coupled electric and magnetic fields that vary periodically as they move through space.

The electric and magnetic fields are perpendicular and described as transverse in nature.

Question 2

Examples of electromagnetic waves

Answer 2

Radio waves, X-rays and infra - red, and light

Question 3

What is the distance between subsequent wave crests known as?

Answer 3

Wavelength. (λ)

Question 4

What is the vertical height of the wave known as?

Answer 4

Amplitude.

Question 5

What is the time taken for corresponding points on a wave to pass a fixed point known as?

Answer 5

Period (T)

Question 6

What is the number of corresponding points passing in unit time known as?

Answer 6

Frequency (f).

Question 7

What is the speed (c) of an electromagnetic wave in a vacuum?

Answer 7

3.0 x 10^8 m/s

Question 8

How are speed, frequency and wavelength related in an equation?

Answer 8

c = f x λ

Question 9

What does frequency (f) equal?

Answer 9

f = 1/T

T = time period

Question 10

What is superposition of waves?

Answer 10

When two or more sinusoid waves act at the same place then the result can be found be adding the individual waves algebraically.

Question 11

What is constructive interference?

Answer 11

If two waves have the same amplitude and frequency and are in phase, the waves will reinforce each other resulting in doubling their amplitudes.

Question 12

What is destructive interference?

Answer 12

If two waves meet that are completely out of phase, at every point the amplitudes have the same magnitude but opposite sign, then they cancel each other out.

Question 13

What is a ray?

Answer 13

Light treated as a form of energy which travels in straight lines.

Question 14

What is a beam?

Answer 14

A collection of rays.

Question 15

What is the law of reflection?

Answer 15

When a bean of light is reflected from a smooth surface, the angle of reflection equals the angle of incidence.

Øi = Ør

Question 16

What is regular reflection?

Answer 16

If a parallel beam of light falls on a plane mirror, it is reflected as a parallel beam

Question 17

What is diffuse reflection ?

Answer 17

If the surface is not smooth or is irregular, the surface will reflect the light diffusely (many directions).

Question 18

What is lateral inversion?

Answer 18

How an object in a mirror appears to be further back within the mirror, and at the same distance as the object is in front of the mirror.

Question 19

What can a laterally inverted image in a plane mirror be described as?

Answer 19

Unreal / virtual

Question 20

What are the features of a concave mirror?

Answer 20

The centre of curvature (C) is in front of the mirror, the centre of the mirror is called pole (P).

A narrow beam of rays is reflected so that all rays coverage to a principal focus point (F) in front of the mirror and is described as REAL as the actually light passes through it.

Question 21

What are the features of a convex (diverging) mirror?

Answer 21

The centre of curvature (C) is behind the mirror.

A narrow beam of rays is reflected to form a divergent beam which appears to come from a point behind the mirror.

It provides a virtual/unreal image.

Question 22

What is spherical aberration?

Answer 22

Light rays from a point on a object that are reflected at different distances from the axis of spherical mirror do not converge at a single point.

Question 23

How do rays behave under spherical aberration?

Answer 23

Rays reflected from outer parts of the mirror converge at focal points closer to the mirror than those reflected near the mirrors axis.

Therefore sharp images are produced at the axis of the mirror.

Question 24

What do concave mirrors with parabolic cross sections produce?

Answer 24

High quality images that do not undergo spherical aberration.

Landing lights, search lights.

Question 25

What three points should be considered when constructing ray diagrams?

Answer 25

1. A ray travelling parallel to the principle axis, which after reflection actually passes through the principle focus or appears to diverge from it. 2. A ray travelling through the centre of curvature which strikes the mirror normally is reflected back along the same path. 3. A ray travelling through the principal focus is reflected parallel to the principal axis.

Question 26

What image does ray diagram 1 produce ?

Answer 26

Real, inverted and diminished.

Question 27

What image does ray diagram 2 produce?

Answer 27

Real, inverted and the same size as the object.

Question 28

What image does ray diagram 3 produce ?

Answer 28

Real, inverted and magnified.

Question 29

What is linear magnification?

Answer 29

A ratio between the size of image and the size of an object.

Question 30

Magnification equation

Answer 30

Magnification = image height / object height = image distance / object distance.

Question 31

Laws of refraction

Answer 31

If light passes obliquely from air to water, its velocity changes which causes its direction to change. This is refraction. The greater the ratio between the velocities in the mediums, the greater the refraction is. The refracted ray is in the same place as the incident ray and the normal to the medium at the point of incidence but in the opposite side of the normal from the incident ray.

Question 32

What happens if light goes from a medium of high velocity to a medium of low velocity? (Air into water)

Answer 32

It will refract towards the normal.

Question 33

What happens if light goes from a medium of low velocity to a medium of high velocity? (Water into air)

Answer 33

It will refract away from the normal.

Question 34

What is the index of refraction?

Answer 34

The ratio between the velocity of light in free space and it’s velocity in the medium. n = c / V Where c = velocity of light in free space, V = velocity of light in the medium

Question 35

What is Snell’s law?

Answer 35

n1 x sin (i) = n2 x sin (Ø)

Question 36

What is dispersion?

Answer 36

The bending power of the material dependant on the frequency.

Question 37

Critical angle of incidence

Answer 37

SinØc = n2 / n1

Question 38

What are the conditions for total internal reflection ?

Answer 38

The light ray must be attempting to travel from a medium of higher refractive index to a medium with a lower refractive index. The angle of incidence must be greater than the critical angle Øc .

Question 39

What is a lens?

Answer 39

A portion of transparent medium bounded by two curves.

Question 40

Convex lenses are …

Answer 40

Thicker in the middle than at the edges and are known as converging lenses.

Question 41

Concave lenses are …

Answer 41

Thinner in the middle than at the edges and are known as diverging lenses.

Question 42

What is the principal axis of a lens ?

Answer 42

A straight line joining two centres of curvature and is perpendicular to the surfaces where it passes through them.

Question 43

What is the principal focus of a lens?

Answer 43

The point in the principal axis to which all the rays close to and parallel to the axis, converge. Or, where they appear to diverge after refraction.

Question 44

What is the optical centre of lens?

Answer 44

A fixed point for any particular lens and coincides with geometric centre of a symmetrical lens.

Question 45

What is the focal length of a lens?

Answer 45

The distance from the principal focus to the optical centre of a lens.

Question 46

What is a fibre optic?

Answer 46

A central core surrounded by a layer of material called cladding, followed by a jacket. The core transmits the light waves and the cladding keeps the light waves within the core and provides strength to the core. The jacket provides protection from moisture and abrasion.

Question 47

What are the advantages of fibre optics ?

Answer 47

They can carry signals with much less energy loss than copper cables and at a higher bandwidth, resulting in more information transmitted longer distances with less repeaters required. They are thinner, lighter and require less insulation space.