11: General Wave Properties

Question 1

Define wave.

Answer 1

A wave is a disturbance that transfers energy from one place to another without transferring matter.

Question 2

How are waves made?

Answer 2

A wave is made up of periodic motion, which is motion repeated at regular intervals.

Question 3

What is a medium?

Answer 3

The substance through which the wave travels (i.e: air, water)

Question 4

Describe how energy is transferred in a medium. [2m]

Answer 4

The source oscillates, transferring energy to the particles within the medium [1m], which vibrate as the wave passes through them. The kinetic energy of the particles is then transferred to the particles furher away [1m], causing them to vibrate as well.

Question 5

Name and define the two types of wave motion.

Answer 5

Transverse wave:
Direction of wave travel is perpendicular to the direction of oscillation.

Longditudinal wave:
Direction of wave travel is parallel to the direction of oscillation.

Question 6

What are the different points of a wave called?

Answer 6

Transverse wave:
Troughs (lowest) and crests (highest).

Longditudinal wave:
Rarefactions (particles far apart) and compressions (particles close together).

Question 7

State a similarity of transverse and longditudinal waves.

Answer 7

Both transfer energy from the source to points further away.

Question 8

Define equilibrium.

Answer 8

The point on a wave where particles rest undisturbed. (i.e: the middle line on a displacement graph)

Question 9

Points in a wave are in phase if they…

Answer 9

…have the same direction of motion, same speed, and same displacement from their equilibrium position.

Question 10

Define wavelength (λ) and state its SI unit.

Answer 10

The shortest distance between any two points in a phase (also the distance between successive wavelengths).

SI unit: metre (m)

Question 11

Define aplitude (A) and state its SI unit.

Answer 11

The maximum displacement of a point from its equilibrium position. (i.e: the value of the crest and trough)

SI unit: metre (m)

Question 12

What does a displacement-distance graph represent?

Answer 12

The displacements of all particles in a wave at a particular point in time.

Question 13

What does a displacement-time graph represent?

Answer 13

The displacements of one particle over a time interval.

Question 14

Define period (T) and state its SI unit.

Answer 14

The time taken to produce one complete wave (also equivalent to the time taken for a wave to travel a distance equal to its wavelength).

SI unit: seconds (s)

Question 15

Define frequency (f) and state its formula and SI unit.

Answer 15

The number of complete waves produced per second.

f = 1/T
SI unit: hertz (Hz)

Question 16

The higher the frequency, the…

Answer 16

…greater number of waves produced per second.

Higher freq. = shorter period

Question 17

Define wave speed (v) and state its formula and SI unit.

Answer 17

The distance travelled by a wave per unit time.

v = fλ

Question 18

Define wave speed (v) and state its formula and SI unit.

Answer 18

The distance travelled by a wave per unit time.

v = fλ
SI unit: metre per second (m s^-1)

Question 19

✰ Define wavefront.

Answer 19

An imaginary line on a wave that joins all adjacent points that are in phase. (They can be straight lines, concentric circles, or any other shape depending on the waves produced.) The distance between successive wavefronts is one wavelength.

Question 20

Explain why, when travelling through water of different depths, the frequency of a wave remains constant, but its wavelength increases in deeper water.

Answer 20

The frequency of a wave depends on the frequency of its source. If the same wave is travelling across water of different depths, its frequency would not change.

Wavelengths of waves are longer in deeper water as the wave speed v of the wave increases, implying an increase in wavelength λ.

[v = fλ, where f is a constant when the source remains unchanged. Therefore, and increase in v implies an increase in λ, and vice-versa.]