waves

Question 1

what is meant by amplitude?

Answer 1

the maximum displacement from a peak or a trough to its equilibrium position.

Question 2

what is meant by displacement?

Answer 2

how far a point on a wave ha moved from its undisturbed position.

Question 3

what is meant by phase and phase difference?

Answer 3

phase is the measurement of a position of a certain point along the wave cycle. phase difference is the amount that one wave lags behind another.

Question 4

what is an electromagnetic wave?

Answer 4

an electromagnetic waves are oscillating electric and magnetic fields that progress through space without need for a substance. the vibrating electric field generates a vibrating magnetic field which generates an vibrating electric field further away and so on.

Question 5

why are transverse waves plane-polarising?

Answer 5

the vibrations only stay in one plane. if the vibrations moved from one plane to another then the waves are unhpolarising.

Question 6

what happens if unpolarised light is passed through a polarising filter?

Answer 6

if unhpolarising light is passed through a filter the transmitted light will be polarised as the filter only lets light through that oscillates in a certain direction.

Question 7

what happens if unpolarised light passes through two filters at 90o to each other?

Answer 7

when the unpolarised light passes through the first filter it will be polarised in the direction of the polarising filter. as the next filter is at 90o the light will not be able to pass through. in this situation the filters are said to be crossed.

Question 8

how do you calculate the period of a wave?

Answer 8

1/f

also known as the period for one cycle.

Question 9

how do you calculate the speed of a wave ?

Answer 9

c=distance travelled in one cycle/time taken for one cycle

= frequency x wavelength

Question 10

what is phase difference measured in?

Answer 10

degrees or radians.

Question 11

how do you calculate phase difference?

Answer 11

2πd/wavelength
d = two points that are a distance apart
1 cycle = 360o = 2π radians

Question 12

how can you study different wave properties?

Answer 12

a ripple tank.

Question 13

what is the principle of superposition?

Answer 13

when two waves meet, the total displacement at a point is equal to the sum of the individual displacements at that point.
when a crest meets a crest a supercrest is formed same with a trough.

Question 14

how do stationary waves form?

Answer 14

when to progressive waves continuously move across each other they combine at fixed points along the rope to form points of no displacement called nodes. at a node the two waves are always 180o out of phase so they cancel each other out.

Question 15

what is a node and a antinode?

Answer 15

a node is a point of no displacement and a antinode is the position of maximum displacement.

Question 16

what is interference?

Answer 16

when waves are continuously passing through each other at a constant frequency ant at a constant wave difference you get cancellation and reinforcement occurring at fixed positions

Question 17

what is half a stationary wave called?

Answer 17

the first harmonic, for the fundamental mode of vibration

Question 18

how do you calculate the distance between adjacent nodes?

Answer 18

1/2 x wavelength

Question 19

what happens to the stationary wave if the frequency is gradually increased?

Answer 19

as the frequency is gradually increased the original pattern disappears and a new one is observed (e.g. the first harmonic changes to the second harmonic)

Question 20

how do stationary waves transfer energy to their surroundings?

Answer 20

stationary waves do not transfer energy to their surroundings because the nodes and anti nodes are in fixed positions

Question 21

how is a stationary wave formed?

Answer 21

consider a snapshot of two progressive waves passing through each other. when they are in phase they reinforce each other to produce a large wave, one quarter of a cycle later they have both moved 1/4 of a wave cycle in opposite directions (they are now in anti phase so cancel each other out) after another 1/4 cycle the waves are back in phase therefore producing one large wave.

Question 22

what happens to the amplitude in a stationary wave pattern?

Answer 22

it varies from 0 to a node to maximum amplitude at an antinode.

Question 23

what happens to the phase difference in a stationary wave pattern?

Answer 23

the phase difference is 0 if the two particles are between adjacent nodes or are separated by an even number of nodes, or 180o if the particles are separated by an odd number of nodes.

Question 24

how do you calculate the first harmonic frequency?

Answer 24

c/2L

where c is the speed of the progressive wave and L is the length of the vibrating section

Question 25

how do you calculate the frequency of the second harmonic?

Answer 25

c/L

Question 26

how do you calculate the third harmonic?

Answer 26

3c/2L

Question 27

how is a stationary wave formed on a vibrating string?

Answer 27

when the wave is reflected the crest reverses its phase and travels back along the strip as a trough. when it reaches the vibrator it reflects and then reverses agin. if this crest is then reinforced by a crest created by the vibrator then the amplitude of the crest is then increased

Question 28

how do you calculate the time taken for the wave to travel along the string and back?

Answer 28

2L/c

Question 29

how can the pitch of a note from a stretched string be altered?

Answer 29

increasing the tension or shortening the length increases the pitch.