Waves

Question 1

What is a progressive wave?

Answer 1

A progressive wave transfers energy without transferring material and is made up of particles of a medium oscillating.

Example: Water waves consist of water particles moving up and down.

Question 2

Define amplitude in the context of waves.

Answer 2

The maximum displacement from the equilibrium position (units are m).

Question 3

What does frequency (f) measure in waves?

Answer 3

The number of complete oscillations passing through a point per second (units are Hz).

Question 4

What is wavelength (λ)?

Answer 4

The length of one whole oscillation, such as the distance between successive peaks or troughs (units are m).

Question 5

How is wave speed (c) calculated?

Answer 5

Speed is equal to the wave’s frequency multiplied by its wavelength: c = f λ.

Question 6

What is phase in wave terminology?

Answer 6

The position of a certain point on a wave cycle, measured in radians, degrees, or fractions of a cycle.

Question 7

What does ‘in phase’ mean?

Answer 7

Two points on a wave are in phase if they are at the same point of the wave cycle, with the same displacement and velocity.

Question 8

What is a transverse wave?

Answer 8

A wave where the oscillation of particles is at right angles to the direction of energy transfer.

Question 9

Give an example of a transverse wave.

Answer 9

All electromagnetic (EM) waves are transverse.

Question 10

What characterizes longitudinal waves?

Answer 10

The oscillation of particles is parallel to the direction of energy transfer.

Question 11

What is polarisation in wave physics?

Answer 11

A polarised wave oscillates in only one plane. Only transverse waves can be polarised.

Question 12

What is the principle of superposition of waves?

Answer 12

The displacements of two waves are combined as they pass each other, resulting in a vector sum of each wave’s displacement.

Question 13

Define constructive interference.

Answer 13

Occurs when two waves have displacements in the same direction.

Question 14

What happens during destructive interference?

Answer 14

One wave has positive displacement and the other has negative displacement, leading to total destructive interference if they are equal and opposite.

Question 15

What is a stationary wave?

Answer 15

A wave formed from the superposition of two progressive waves travelling in opposite directions with the same frequency, wavelength, and amplitude.

Question 16

What are antinodes?

Answer 16

Regions of maximum amplitude formed where waves meet in phase.

Question 17

What are nodes in a stationary wave?

Answer 17

Regions of no displacement formed where waves meet completely out of phase.

Question 18

How is the first harmonic defined?

Answer 18

The lowest frequency at which a stationary wave forms, characterized by two nodes and a single antinode.

Question 19

What is the formula for calculating the frequency of harmonics?

Answer 19

The frequency of the first harmonic can be used to find higher harmonics by doubling for the second harmonic, tripling for the third harmonic, etc.

Question 20

What does path difference refer to in wave interference?

Answer 20

The difference in the distance travelled by two waves.

Question 21

What is a coherent light source?

Answer 21

A source that has the same frequency and wavelength with a fixed phase difference.

Question 22

Describe Young’s double slit experiment.

Answer 22

An experiment that demonstrates interference of light from two coherent sources, forming a pattern of light and dark fringes.

Question 23

What is diffraction?

Answer 23

The spreading out of waves when they pass through or around a gap.

Question 24

What is a diffraction grating?

Answer 24

A slide containing many equally spaced slits that enhances the sharpness and brightness of interference patterns.

Question 25

What is the formula associated with diffraction gratings?

Answer 25

d sinθ = nλ, where d is the distance between the slits, θ is the angle to the normal, n is the order, and λ is the wavelength.

Question 26

True or False: All electromagnetic waves can be polarised.

Answer 26

False.

Question 27

Fill in the blank: The speed of a wave is equal to the wave’s frequency multiplied by its _______.

Answer 27

[wavelength].

Question 28

What is the equation for the first maximum in diffraction?

Answer 28

d sin θ = λ

This relates the slit separation (d), the angle of diffraction (θ), and the wavelength (λ) for the first order.

Question 29

What is the general equation for maxima in diffraction?

Answer 29

d sin θ = nλ

Here, n is an integer representing the order of the maximum.

Question 30

What is a diffraction grating used for in astronomy?

Answer 30

To obtain line absorption spectra from starlight

This helps identify the elements present in stars.

Question 31

What is the formula for calculating the refractive index (n)?

Answer 31

n = c / cs

Where c is the speed of light in a vacuum and cs is the speed of light in the material.

Question 32

What does a higher refractive index indicate?

Answer 32

The material is more optically dense

Air has a refractive index of approximately 1.

Question 33

What occurs during refraction?

Answer 33

A wave changes direction when entering a different medium

The direction depends on the refractive indices of the materials.

Question 34

What is Snell’s law?

Answer 34

n1 sin θ1 = n2 sin θ2

Used for calculations involving the refraction of light.

Question 35

What happens to light when it moves from a less optically dense medium to a more optically dense medium?

Answer 35

It bends towards the normal

The speed of light decreases in the more dense medium.

Question 36

What is the critical angle (θc)?

Answer 36

The angle of incidence where light is refracted along the boundary

It can be calculated using sin θc = n2 / n1 when n1 > n2.

Question 37

What is total internal reflection (TIR)?

Answer 37

Occurs when the angle of incidence is greater than the critical angle

The incident refractive index must be greater than the refractive index of the second material.

Question 38

What is the purpose of optical fibers?

Answer 38

To carry information in the form of light signals

They consist of an optically dense core surrounded by cladding.

Question 39

What causes signal degradation in optical fibers?

Answer 39

Absorption and dispersion

These can lead to loss of information.

Question 40

What is modal dispersion?

Answer 40

Caused by light rays entering the fiber at different angles

This leads to pulse broadening as rays take different paths.

Question 41

How can modal dispersion be reduced?

Answer 41

By making the core very narrow

This minimizes differences in path lengths.

Question 42

What is material dispersion?

Answer 42

Caused by using light of different wavelengths

This leads to pulse broadening as rays travel at different speeds.

Question 43

How can material dispersion be prevented?

Answer 43

By using monochromatic light

This ensures that all light rays travel at the same speed.

Question 44

What is an optical fiber repeater?

Answer 44

A device that regenerates signals during travel

It helps reduce signal degradation.