3.1 Progressive And Stationary Waves

Question 1

Define frequency and give units

Answer 1

Number of waves passing a point per second

Hz (Hertz)

Question 2

Define wavelength

Answer 2

The distance between 2 adjacent peaks/troughs on a wave

Question 3

Define amplitude

Answer 3

Max. displacement of wave from equilibrium position

Question 4

How can you find out time period of a wave using its frequency

Answer 4

T= 1/f

Question 5

What’s phase difference and what’s it measured in

Answer 5

How much a wave lags behind another wave

Measured in radians, degrees or fraction of a cycle

Question 6

What’s a longitudinal wave

Answer 6

Where oscillation of particles is parallel to direction of energy transfer

Rarefactions (low pressure areas)

Compressions (high pressure areas)

Question 7

What’s a transverse wave

Answer 7

Waves where particle oscillations are perpendicular to direction of energy transfer

Question 8

How fast do EM waves travel in a vacuum

Answer 8

3x10^8 m/s

Question 9

True or False? Magnetic field and electric field in an EM wave are parallel to each other

Answer 9

False

Electric and magnetic field are at 90 to each other (perpendicular)

Question 10

What does a polarising filter do

Answer 10

Only allows oscillations in one plane

Question 11

How is polarisation used as evidence of nature of transverse waves

Answer 11

It can only occur if a waves oscillation are perpendicular to its direction of travel (as they are in transverse waves)

Question 12

How’s polarisation used in antennas

Answer 12

TV and radio signals are usually plane-polarised by orientation of rods on transmitting aerial, so receiving aerial must be aligned in same plane of polarisation to receive signal at full strength

Question 13

What’s a stationary wave

Answer 13

Wave which transfers no energy and whose positions of max. and min. amplitude are constant

Question 14

What’s a node

Answer 14

Point on a stationary wave where the displacement is 0

Question 15

What’s an antinode

Answer 15

Point on a stationary wave with max. displacement

Question 16

What are conditions for a stationary wave to be produced

Answer 16

Waves must be of same frequency, wavelength and amplitude

Must be travelling in opposite directions

Conditions are often met when a wave is reflected back onto itself

Question 17

How are stationary waves produced

Answer 17

When 2 progressive waves that are travelling in opposite directions in same plane superpose each other and have the same frequency, wavelength and amplitude

Question 18

What’s constructive interference

Answer 18

Where waves meet in phase and so antinodes (regions of max. amplitude) form

Question 19

What’s destructive interference

Answer 19

Where waves are completely out of phase and so nodes (regions of no displacement) form

Question 20

Describe first harmonic for a stationary wave with 2 closed ends

Answer 20

Consists of 2 nodes at either end and an antinode in the middle

Question 21

Describe second harmonic with one open end and one closed end

Answer 21

Consists of 2 nodes and 2 antinodes with one of the nodes at closed end and one antinode at open end

Question 22

What’s a progressive wave

Answer 22

Transfers energy from one point to another without transfer of material

Question 23

Diff between progressive and stationary

Answer 23

Progressive transfers energy and stationary doesn’t