Characteristics of Waves Science A Physics – P1 Topic 5a : Characteristics of Waves

What is a Wave? All waves carry energy without transferring matter. Light, infra red, and microwaves all make things warm up (which shows that they can carry energy). Loud sounds can make things vibrate or move. Even the quietest sound can move your ear drum.

Amplitude (A) When a wave travels through any material, it causes the particles making up that material, to move from their position of rest. The particles can be moved a little or a lot. The maximum movement away from the rest position is known as the amplitude.

Amplitude (A) The amplitude corresponds to the loudness which is measured in decibels (dB). The amplitude is a measure of the energy carried by the wave. The greater the amplitude, the louder the sound, and the more energy it has. Loud sound Quiet sound This is where an amplifier gets its name - an amplifier makes sounds louder.

Wavelength () The wavelength is one complete wave cycle. It is the distance between any specific point on one wave and the same point on the next wave. For example, from peak to peak or trough to trough. Wavelength is given the symbol  after the Greek letter lambda.

Example: What is the amplitude and wavelength of the wave below: Wavelength = 0.5 cm Amplitude = 10cm Amplitude = 10cm Wavelength = 0.5 cm Wavelength = 0.5 cm Amplitude = 10cm Amplitude = 10cm Wavelength = 0.5 cm

Activity 1 Now Complete Exercise 1.

Question 1 Amplitude = 5 cm Wavelength = 4 cm Horizontal displacement (cm) Amplitude = 5 cm Wavelength = 4 cm

Question 2 Amplitude = 3 cm Wavelength = 10 cm Horizontal displacement (cm) Amplitude = 3 cm Wavelength = 10 cm

Question 3 Amplitude = 10 cm Wavelength = 20 cm Horizontal displacement (cm) Amplitude = 10 cm Wavelength = 20 cm

Question 4 Amplitude = 8 cm Wavelength = 6 cm Horizontal displacement (cm) Amplitude = 8 cm Wavelength = 6 cm

Question 5 Amplitude = 4 cm Wavelength = 3.2 cm

Q6 – Amplitude 4 cm, Wavelength 8 cm

Q7 – Amplitude 3.5 cm, Wavelength 6 cm

Q8 – Amplitude 2 cm, Wavelength 5 cm

Q9 – Amplitude 3 cm, Wavelength 6 cm

Frequency (f) Wave frequency relates to the number of waves per second. 1 second for waveform to pass The number of waves passing a specific point per second, is known as the frequency. It is measured in units called hertz (Hz). If the above wave took one second, it has a frequency of 4Hz. The pitch of a sound is determined by its frequency.

High frequency - High pitch Low frequency - Low pitch Frequency (f) All sounds are made by objects vibrating. The faster that an object vibrates, the higher the pitch of the sound produced. The more frequent the vibrations, the greater the frequency. High frequency - High pitch Low frequency - Low pitch

Wave Equation All waves obey the wave formula: = Wave Speed (v) (v) Frequency (f) x (f) Wavelength () () (metre/second, m/s) (Hertz, Hz) (metre, m) Point the cursor over the formula triangle to show the 3 formulas...

Example. 3 waves travel at the same speed but have different frequencies & wavelengths. Complete the Table Speed (m/s) Frequency (Hz) Wavelength (m) Wave 1 16 8 Wave 2 32 Wave 3 2 16 x 8 = 128 m/s 128  32 = 4 m 128 m/s 128  2 = 64 Hz 128 m/s

Activity 2 Now Complete Exercise 2.

2 × 12 = 24 m/s 5 × 12 = 60 m/s 10 × 12 = 120 m/s 20 × 12 = 240 m/s These waves all have a wavelength of 12m. Calculate their speed if they have the following frequencies. 2Hz ........... 5Hz ……….. 10Hz ……… 20Hz ……… 1Hz ……….. 0.5Hz ……... 1000Hz …… 8Hz ………. 2 × 12 = 24 m/s 5 × 12 = 60 m/s 10 × 12 = 120 m/s 20 × 12 = 240 m/s 1 × 12 = 12 m/s 0.5 × 12 = 6 m/s 1000 × 12 = 12000 m/s 8 × 12 = 96 m/s

These waves have a frequency of 10Hz These waves have a frequency of 10Hz. Find the wavelength if they have the following speed. 3 m/s ........... 40 m/s…….. 100 m/s…… 0.3 m/s …… 2500 m/s….. 0.2 m/s …... 50 m/s …… 20 m/s ……. 3 ÷ 10 = 0.3 m 40 ÷ 10 = 4 m 100 ÷ 10 = 10 m 0.3 ÷ 10 = 0.03 m 2500 ÷ 10 = 250 m 0.2 ÷ 10 = 0.02 m 50 ÷ 10 = 5 m 20 ÷ 10 = 2 m

These waves have a wave speed of 4 m/s These waves have a wave speed of 4 m/s. Find the frequency if they have the following wavelength. 2 m ........... 8 m …….... 0.5 m …..… 40 m …..… 0.4 m ….…. 0.2 m …..... 50 m ……… 20 m …..…. 4 ÷ 2 = 2 Hz 4 ÷ 8 = 0.5 Hz 4 ÷ 0.5 = 8 Hz 4 ÷ 40 = 0.1 Hz 4 ÷ 0.4 = 10 Hz 4 ÷ 0.2 = 20 Hz 4 ÷ 50 = 0.08 Hz 4 ÷ 20 = 0.2 Hz

An alternative method to calculate speed. Speed can also be calculated using the formula below: Speed (m/s)= Distance (m) Time (s)

d This can also be remembered as a triangle. Just cover the part you want to find to reveal the formula needed. e.g to find time, cover t and we are left with d s x t

The ripples on a pond take 4s to travel 0. 8m The ripples on a pond take 4s to travel 0.8m. Calculate the speed of the ripples. = 0.8/4 = 0.2 m/s

Waves - Key Terms

Practical Investigation 1. Activity 3 Now Complete Practical Investigation 1.