waves

Question 1

what is a progressive wave?

Answer 1

• a wave that transfers energy from one point to another without transferring the medium itself

Question 2

what is the displacement of a wave?

Answer 2

• distance of a point on the wave from its equilibrium position

Question 3

what is the amplitude of a wave?

Answer 3

• maximum displacement of a particle in the wave from its equilibrium position

Question 4

what is wavelength?

Answer 4

• distance between points on successive oscillations of the wave that are in phase

Question 5

what is the period of a wave?

Answer 5

• time taken for one complete oscillation

Question 6

what is the frequency of a wave?

Answer 6

• number of oscillations per unit time

Question 7

what is phase difference?

Answer 7

• a measure of how much a point on a wave is infront or behind another

Question 8

what happens when crests or troughs are aligned?

Answer 8

• waves are in phase

Question 9

what happens when crest aligns with troughs?

Answer 9

• waves are in antiphase

Question 10

what are transverse waves?

Answer 10

• waves which the particles oscillate perpendicular to direction of wave travel

Question 11

what are longitudinal waves?

Answer 11

• waves which oscillate parallel to direction of wave travel

Question 12

what are compressions?

Answer 12

• regions of increased pressure

Question 13

what are rarefactions?

Answer 13

• regions of decreased pressure

Question 14

give 3 examples of transverse waves

Answer 14

• electromagnetic waves
• waves on a string
• vibrations on a guitar string

Question 15

give 3 examples of longitudinal waves

Answer 15

• sound waves
• ultrasound waves
• waves through a slinky coil

Question 16

what is polarisation?

Answer 16

• when particle oscillations occur in only one of the directions perpendicular to the direction of wave travel

Question 17

explain the effect of a polarising filter

Answer 17

• restricts oscillations of the wave into a certain direction depending on axis
• intensity of light will decrease

Question 18

explain what happens if unpolarised light is placed infront of two identical polarising filters, with their transmission axis parallel

Answer 18

• filter A will polarise the light in a certain axis
• all of the polarised light will pass through filter B unaffected
• maximum intensity of light observed

Question 19

explain what happens as filter B is rotated anticlockwise at an angle

Answer 19

• intensity of light changes depending on angle
• when A and B have their transmission axis perpendicular to each other, intensity is minimum

Question 20

what graph and equation will intensity of light follow?

Answer 20

cos graph

I = Io cos^2theta

Question 21

how are stationary waves produced?

Answer 21

• superposition of two waves with same frequency and amplitude travelling in opposite directions

Question 22

how do stationary waves differ from progressive waves?

Answer 22

• they store energy, not transfer
• they have nodes and antinodes
• each point has a diff amplitude depending on amount of superposition

Question 23

what are nodes and antinodes?

Answer 23

nodes are regions of no vibration

antinodes are regions of maximum vibrations

Question 24

what is the principle of superposition?

Answer 24

• when two or more waves with the same frequency and amplitude arrive at a point, the resultant displacement is the sum of the displacement of each wave

Question 25

what happens when two progressive waves arrive in phase?

Answer 25

- they cause constructive interference, peaks and troughs line up on both waves - resultant wave has double the amplitude

Question 26

what happens when two progressive waves arrive in antiphase?

Answer 26

- destructive interference occurs - peaks on one wave line up with troughs on other wave, resultant wave has no amplitude

Question 28

whats the rule for number of antinodes and nodes on a stationary wave for harmonics

Answer 28

nth harmonic has n antinodes and n+1 nodes

Question 29

how do you calculate frequency of first harmonic

Answer 29

v = sqrt T / u v = f lambda = f x 2l 2fl = sqrt T / u f = 1/2l sqrt T / u

Question 30

what is constructive interference

Answer 30

when two waves arrive in phase their combind effect makes resultant amplitude larger

Question 31

what is destructive interference

Answer 31

when two waves arrive in antiphase, their combined effect means they cancel each other out

Question 32

what is meant by coherent sources

Answer 32

- same frequency - constant phase difference

Question 33

what is meant by path difference

Answer 33

- difference in distance travelled by two waves from their sources to the point where they meet