Waves

Question 1

What is a longitudinal wave?

Answer 1

A wave in which the direction of vibration of the particle is parallel to the direction in which the wave travels (propagates). Longitudinal waves have compressions and rarefactions.

Question 2

What is a transverse wave?

Answer 2

A wave in which the direction of vibration of the particle is perpendicular to the direction in which the wave travels (propagates). Transverse waves have peaks and troughs.

Question 3

Give 2 examples of longitudinal waves

Answer 3

Sound waves and primary seismic waves

Question 4

Give 2 examples of transverse waves

Answer 4

Electromagnetic waves and vibrations in strings

Question 5

What is polarisation?

Answer 5

Vibrations in on plane only

Question 6

Can longitudinal waves be polarised?

Answer 6

No, only transverse waves can be polarised.

Question 7

What is the displacement?

Answer 7

distance and direction from equilibrium position

Question 8

What is the amplitude

Answer 8

maximum displacement of a vibrating particle.

Question 9

What is the phase difference between two particles?

Answer 9

the fraction of a cycle between the two vibrations.

Question 10

What is refraction?

Answer 10

When waves pass across a boundary between two mediums, they change speed and hence direction. When it enters a less dense substance, the speed increase and thus the wave refracts away from the normal.

Question 11

What is diffraction?

Answer 11

the spreading out of waves when they pass through a gap or by an obstacle. The narrower the gap, the more the waves spread out.

Question 12

What is superposition?

Answer 12

When waves pass through each other they combine, can be destructive or constructive.

Question 13

What are stationary waves?

Answer 13

formed from two progressive waves. Have points of cancellation and reinforcement.

Question 14

What are nodes?

Answer 14

points of no displacement

Question 15

what are anti-nodes

Answer 15

points of maximum displacement

Question 16

What is interference?

Answer 16

as waves pass through each other at constant frequency and constant phase difference, cancellation and reinforcement occurs at fixed positions.

Question 17

What are coherent sources of waves?

Answer 17

same frequency with a constant phase difference.

Question 18

Do freely vibrating stationary waves transfer energy?

Answer 18

no

Question 19

What is the phase difference between two vibrating particles on a stationary wave?

Answer 19

zero- if the particles are separated by an even number of nodes. or adjacent nodes,
180 degrees- if the two particles are separated by an odd number of nodes.

Question 20

Differences between stationary and progressive waves

Answer 20

for progressive waves, all particles vibrate at same frequency and same amplitude. for stationary waves, all particles except those at nodes vibrate at the same frequency. amplitude varies from zero at nodes to maximum at antinodes.

Question 21

What does the pitch of a note correspond to?

Answer 21

frequency

Question 22

Explain how an oscilloscope works

Answer 22

uses two pairs of deflecting plates, one horizontal and one vertical. electron is deflected by the plates which will alter its position on the screen. the displacement of the spot is proportional to the applied pd.

Question 23

Why does refraction occur?

Answer 23

this is because the speed of the light waves is different in each substance.

Question 24

What are the conditions for total internal reflection

Answer 24

the incident substance has a larger refractive index than the other substance.
the angle of incidence exceeds the critical angle

Question 25

What happens when light diffracts through two slits?

Answer 25

alternate bright and dark fringes appear on the screen, they are the same width. fringes are evenly spaced and parallel to the double slits.

Question 26

Why are dark and bright fringes formed in double slit interference?

Answer 26

light fringes occur when waves arrive in phase with each other. Where a dark fringe is formed, light arrives 180 degrees out of phase and so the two sources cancel each other out.

Question 27

To measure the fringe separation, why would you measure across several fringes?

Answer 27

It reduces the percentage error in the readings.

Question 28

Why are the double slits described as coherent sources?

Answer 28

they emit light waves of the same frequency with a constant phase difference.

Question 29

how does laser light differ from non-laser light?

Answer 29

laser light is highly monochromatic

laser light is a source of coherent light

Question 30

What is observed when light is diffracted by a single slit?

Answer 30

the central fringe is twice as wide as each of the outer fringes. The intensity of each fringe decreases with greater distance from the central fringe. The outer fringes are much less intense than the central fringe. Each of the outer fringes is the same width.

Question 31

Why is light transmitted by a diffraction grating in certain directions only?

Answer 31

because the light passing through each slit is diffracted, the diffracted light waves from adjacent slits reinforce each other in certain directions only, and cancel out in all other directions.