Waves and optics- waves (4)

Question 1

Define frequency and give its units

Answer 1

The number of waves passing through a point per second

(hertz) Hz

Question 2

Define wavelength

Answer 2

The distance between two adjacent peaks on a wave

Question 3

Define amplitude

Answer 3

The maximum displacement of the wave from its equilibrium point

Question 4

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

Answer 4

T= 1/f

Question 5

What is phase difference and what is it measured in?

Answer 5

How much a wave lags behind another wave.

Mesured in radians, degrees or fractions of a cycle

Question 6

What is a longitudinal wave?

Answer 6

A wave in which the oscillations of the particles are parallel to the direction of energy transfer
There are rarefractions and compressions

Question 7

What is a transverse wave? Give examples

Answer 7

Waves where the particles oscilations are perpendicular to the direction of energy transfer.
For exaple: electromagnetic waves

Question 8

How fast do electromagnetic waves travel in a vacuum?

Answer 8

3 x 10^8 m/s

Question 9

True of false? The magnetic field and electric field in an electromagnetic wave are parallel to each other.

Answer 9

False

The electric and magnetic field are at right angles to each other.

Question 10

What does a polarising filter do?

Answer 10

Only allows oscillations in one plane

Question 11

How is a polarising filter used as evidence of the nature of transverse waves?

Answer 11

Polarisation can only occur if a wave’s oscillations are perpendicular to its direction of travel (as theyare in transverse waves)

Question 12

How are polarisers used in antennas?

Answer 12

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

Question 13

What is a stationary wave?

Answer 13

A wave which transfers no energy and where the postions of maximum and minimum amplitude are constant

Question 14

What is a node?

Answer 14

A point on a stationary wave where the displacement is 0

Question 15

What is an antinode?

Answer 15

A point on a stationary wave with maximum displacement

Question 16

What are the conditions for a stationary wave to be produced?

Answer 16

• The waves must be of the same frequency, wavelength and amplitude
• They must be travelling in opposite directions
  These conditions are often met when a wave is reflected back onto itself

Question 17

How are stationary waves produced?

Answer 17

A stationary wave is formed from the superpostion of 2 progressive waves, travelling in opposite directions in the same plane, with the same frequency, wavelength and amplitude.

• Where the waves meet in phase, constructive interference occurs so antinodes form
• Where the waves meet completely out of phase, destructive interference occurs and nodes form.

Question 18

Describe the first harmonic for a stationary wave with two closed ends

Answer 18

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

Question 19

Describe the second harmonic for a stationary wave with one open end and one closed end

Answer 19

It consists of two nodes and two antinodes, with one of the nodes at the closed end and one of the antinodes at the open end