Section 3 - Waves: 3.1 - Progressive and Stationary Waves

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 position.

Question 4

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

Answer 4

T = 1/f

Question 5

What is phase difference, and what is it measured in?

Answer 5

How much a particle / wave lags behind another particle / wave. Measured in radians, degrees, or fractions of a cycle.

Question 6

What is a longitudinal wave?

Answer 6

A wave in which the oscillation of the particles is parallel to the direction of energy transfer.
There are rarefactions (areas of low pressure) and compressions (areas of high pressure).

Question 7

What is a transverse wave? Give examples.

Answer 7

Waves where the particle oscillations are perpendicular to the direction of energy transfer.
For example: electromagnetic waves

Question 8

How fast do electromagnetic waves travel in a vacuum?

Answer 8

3 x 10^8 m/s

Question 9

True or False? The magnetic field and electric field in a 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 polarisation 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 they are in transverse waves).

Question 12

How are polarisers used in antennas?

Answer 12

TV and radio signals 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 receive the signal at full strength.

Question 13

What is a stationary wave?

Answer 13

A wave which transfers no energy and whose positions 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 superposition 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 (regions of maximum amplitude) form.
● Where the waves meet completely out of phase, destructive interference occurs and nodes (regions of no displacement) 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.