Questions
Waves - Sound - Light – Water
The best way to remember the information in this chapter is to get a pen and paper and write down your answers
before clicking on the Answer link which will take you to the correct page. You may have to read through some of the page before you find the answer, if the answer you have written is not right; change it to the correct answer by copying down the information from the correct page.
What do Waves do
2
Describe the movement of Particles in a Longitudinal Wave.
3
Give an Example of something which travels as a Longitudinal Wave.
4
Describe the movement of Particles in a Transverse Wave.
5
How would you measure the Amplitude of a Transverse Wave?
6
What does the Amplitude tell you about a Wave?
7
How would you measure the Wavelength of a Transverse Wave?
8
What Unit is Wavelength measured in?
9
Define Frequency.
10
What Unit is Frequency measured in?
11
What is the Period of a Wave?
12
Give the Equation which connects Period and Frequency.
13
Give the Equation which connects Velocity, Frequency and Wavelength.
14
What Velocity has a Wave with Frequency 3250 Hz and Wavelength 0·1 m?
15
What Wavelength has a Wave with Frequency 500 Hz and Velocity 330 m/s?
16
What Frequency has a Wave with Wavelength 10 m and Velocity 25 m/s
· Waves transmit energy without transmitting matter. This means that waves can move energy (or information)
from one place to another without moving any substance (stuff) from one place to another.
The amount of energy which a wave has depends on its amplitude.
· Most waves move through substance but only move it backwards and forwards (longitudinal) or side to side (transverse) while the wave passes. After the wave has gone, the substance is back where it started but energy has been carried by the wave from its origin (where it begins) to its destination (where it finishes).
One type of wave (electromagnetic) does not need any substance to get it from its origin to its destination.
It can travel through a vacuum (nothing) so these waves can travel from stars to planets through space
(space is a vacuum). When a longitudinal wave moves through a material, the particles of the material move backwards and forwards
along the direction in which the wave is travelling. Below is a picture of a longitudinal wave travelling along a spring.
· Rarefaction (pronounced rair - ree - fac - shun) is the name given to the region where the coils of the spring are pulled apart.
· Compression is the name given to the region where the coils of the spring are pushed together.
· The wavelength can be measured as the distance between the centres of two compressions. Examples of longitudinal waves are ( Sound) Transverse Waves.
to the direction in which the wave is traveling. The particles either move up and down or from side to side
as the wave goes past (like waves on the surface of the sea). After the wave has gone, the particles are back where they started.
Electromagnetic waves are transverse waves which do not need a substance to travel through
Below is a picture of a transverse wave.
The amplitude of the wave : is measured from the peak (or trough) to the mid-point.
Amplitude can be defined as "the maximum displacement from the average position".
Amplitude is a measure of how much energy the wave has.
The wavelength : is the distance between two peaks or the distance between two troughs.
Wavelength can be defined as "the distance the wave has traveled during one complete cycle".
Wavelength is given the symbol l(Greek lambda, pronounced lam-der), and is measured in metres because it is a distance.
Frequency is defined as "the number of complete cycles (complete waves) in one second".
Hertz is the unit of frequency (symbol Hz).
1 Hertz = 1 cycle per second.
The period of a wave is defined as "the time taken for one complete cycle".
The period = 1 ÷ frequency. This can be rearranged to give
Frequency = 1 ÷ period. The only equation you need for waves is
Velocity or Speed = Frequency x Wavelength
v = f x lThis equation is important!
The equation can be rearranged to give
Q1. A sound wave has a frequency of 3250 Hz and a wavelength of 0·1 m. What is its velocity?
A1. Use v = f x l
v = 3250 x 0·1 = 325 m/s.
Q2. A sound wave travels with a velocity of 330 m/s and has a frequency of 500 Hz. What is its wavelength?
A2. Use l = v ÷ f Q3. A wave at sea travels with a velocity of 25 m/s. If it has a wavelength of 10 m, what is its frequency?
A3. Use f = v ÷ l
f = 25 ÷ 10 = 2·5 Hz.
Note - always make sure that you give the units for your answer and that the units are correct.
If the wavelength is given in centimeters, convert it to metres before doing the calculation.