Topic 4 - Waves

Question 1

Displacement

Answer 1

The distance from the equilibrium position at an instant in time.

Question 2

Amplitude

Answer 2

The amplitude of an oscillator is the maximum displacement of the particles from the equilibrium position.

Question 3

Time Period (T)

Answer 3

The time taken by a wave to complete one full cycle. It can be measured as the time it takes to
oscillate from a point back to the same point in the next cycle.

Question 4

Frequency

Answer 4

Frequency is a measure of how often something happens, in this case how many complete oscillations occur in every second. It is linked to time period of the wave.

Question 5

Phase Difference

Answer 5

The phase difference of two waves is the horizontal distance a similar part of one wave leads or lags the other wave.

Phase difference is measured in fractions of a wavelength, degrees or radians.

Question 6

Superposition of waves

Answer 6

Superposition is when two waves are superimposed on eachother and add up.

The phenomenon is described by the Principle of Superposition, which states:

When two waves are travelling in the same direction and speed, at any point on the combined wave the total displacement of any particle equals the vector sum of displacements of the waves.

Question 7

Constructive interference

Answer 7

When two waves of identical wavelength are in phase, they form a new wave with an amplitude equal to the sum of their individual amplitudes.

Question 8

Destructive interference

Answer 8

Destructive interference occurs when the peaks of one wave overlap the troughs, or lowest points, of another wave (when the maxima of two waves are 180 degrees out of phase). As the waves pass through each other, the peaks and troughs cancel each other out to produce a wave with zero amplitude.

Question 9

Features of Simple Harmonic Motion

Answer 9

1. the acceleration of the object is directly proportional to its displacement
   from its equilibrium position.
2. the acceleration is always directed towards the equilibrium position.

Question 10

Longitudinal Waves

Answer 10

A wave where the displacement of the medium, direction of propagation and direction of energy transfer are all parallel.

e.g. sound waves

Question 11

Transverse Waves

Answer 11

a transverse wave; the oscillations are perpendicular to the direction of propagation and energy transfer.

e.g. water, the waves of the EM spectrum

Question 12

The Electromagnetic Spectrum in the order of decreasing wavelength.

Answer 12

radio, microwave, infra-red, visible, ultraviolet, X-ray, gamma rays

Question 13

Standing Waves

Answer 13

Standing wave, also called stationary wave, is a combination of two waves moving in opposite directions, each having the same amplitude and frequency snd speed.

Question 14

Coherence (of waves)

Answer 14

For two waves to be coherent they need to maintain constant phase difference.

Question 15

Diffraction

Answer 15

Diffraction is when waves pass through a gap and spread out.
The amount of diffraction depends on the size of the
wavelength compared to the size of the gap.

Question 16

The meaning of plane polarisation of light waves

Answer 16

When light waves vibrates or oscillates in only one plane

Question 17

Why sound waves cannot be plane-polarised

Answer 17

Sound waves are longitudinal. Only transverse waves can be plane polarized.

Question 18

What is the refractive index?

Answer 18

The refractive index of a material is a measure of how easy it is for light to travel through it.

Question 19

Refraction

Answer 19

refraction is the change in direction of a wave passing from one medium to another caused by its change in speed.

Question 20

What is a node ?

Answer 20

A node is a position on a wave where the displacement of the medium is always zero

Question 21

What happens to the frequency when a wave passes from one medium to another?

Answer 21

frequency is unchanged.

Question 22

What happens to speed when a wave passes from a less optically dense medium to a more optically dense medium?

Answer 22

Speed decreases i.e., the wave slows down

Question 23

The visible light spectrum in order of longest to shortest wavelength and lowest to highest frequency.

hint: remember roy.g.biv

Answer 23

red, orange, yellow, green, blue, indigo, violet

Question 24

What is meant by the phase difference?

Answer 24

“The cycle difference between two waves at the same point”.

The phase difference between two points depends on the fraction of a whole cycle that lies between them. (Their positions!)

Question 25

What is meant by the refractive index?

Answer 25

The refractive index determines how much the path of a light ray is bent, or refracted, when entering a material. (linked to snells law)

Question 26

What is meant by the critical angle?

Answer 26

The critical angle is the angle of incidence, for which the angle of refraction is 90°.

Question 27

What are harmonics?

Answer 27

The frequencies at which standing waves are formed.

The first harmonic is the lowest frequecy at which a standing wave is formed

Question 28

What is meant by the superposition of waves?

Answer 28

When two waves meet, the resultant displacement is the sum of their individual displacements.

Question 29

(Double slit experiment) How are minima formed in the interference pattern?

Answer 29

The light waves from the two slits interfere (superpose).

When they are a half wavelength out of phase, minima form due to destructive interference.

Question 30

What is the relationship between the wavelength of light and the refractive index?

Answer 30

Lower refractve index (of the material which the light is travelling in) means longer wavelength. and vice versa

Question 31

What harmonics are possible, when you have a pipe with one closed end and one open end?

Answer 31

Only odd harmonics (i.e. 1,3,5,7,9… etc)