Waves GCSE Physics

Objectives of the Lesson Understand the concept of wave motion in the physical world Recall that there are two types of wave motion- Longitudinal and Transverse Explain the difference between the types of waves and use the correct terms for each State some examples of each of the types of wave motion

Waves Introduction A wave can be described as a disturbance that travels through a medium from one place to another. Medium – a substance which something is transmitted or carried through e.g.. air

Examples of waves Sea wave (medium- liquid, water) Shotgun blast (medium- gas, air)

Types of Waves- Transverse Wave motion vs Particle motion

Watch one particle Describe its motion

Transverse wave… In terms of the wavelength, what is the length of the red line on the graph? Wavelength λ – distance from one point on one wave to the same point on the next wave (for example- from crest to crest) CrestCrest TroughTrough Wavelength λ Wave spreads Wave movement Light travels as a transverse wave Wave movement is at right angles to the direction that the wave is travelling Amplitude – maximum displacement from its undisturbed position Amplitude

Types of Waves- Longitudinal Wave motion vs Particle motion

Keep your eye on 1 particle Describe its motion

If the diagram shows the motion of the wave in 1 second then what is the frequency of the wave? Frequency – the number of waves passing a point every second (Hz) Longitudinal wave Rarefaction Compression Sound waves travel as longitudinal waves Wave movement is parallel to the direction the wave is travelling

Water Waves Water waves are an example of waves that involve a combination of both longitudinal and transverse motions. As a wave travels through the water, the particles travel in clockwise circles.

Longitudinal Vs Transverse Create a table with two column headings, Longitudinal and Transverse Wave motion is at right angles to the direction of the wave Wave motion is parallel to the direction of the wave Amplitude is maximum displacement from the wave’s rest position Frequency is the number of waves passing a point in one second Wavelength is the distance from one crest to the next crest Wavelength is the distance from one compression to the next compression This is how sound energy moves This is how light travels

Graph action…

Objectives of the Lesson Recall the wave equation and use it to solve simple problems Describe, using simple wavefront diagrams, how plane waves are reflected at a plane barrier, refracted at a plane boundary

The Wave Equation Speed (v) = Frequency (f) x Wavelength (λ) m/s Hz m

Example What is the speed of a water wave of frequency 4 Hz and wavelength 3 cm? v = f x λ = 4 x (3 / 100) = 0.12 m/s

Try this one… What is the wavelength of a sound wave of frequency 264 Hz and speed 330 m/s? v = f x λ 330 = 264 x λ λ = 330 / 264 = 1.25 m What is the distance between one compression and the next rarefraction on this wave? 1.25 / 2 = m

Question Time Pg 105 Question 1 a) parts i) – iv)

Objectives of the Lesson Describe, using simple wavefront diagrams, how plane waves are reflected at a plane barrier, refracted at a plane boundary

Ripple Tank Wave motion Crest Trough

Wave Diagrams Law of Reflection- The angle of incidence is always equal to the angle of reflection Wave front (crest)

The angle the wave hits the barrier at is 23 degrees. 1. What is the angle of incidence? 2. Draw the three waves after they have hit the barrier and label the angle of reflection and include the normal line. Example 23º Normal line Angle of incidence 67º Angle of reflection 67º

Objectives of the Lesson Describe, using simple wavefront diagrams, how plane waves are reflected at a plane barrier, refracted at a plane boundary

Shallow water Deep water

Refraction- For a wave moving from deep to shallow, the wavelength will shorten because the wave slows down. The f ff frequency of the wave stays the same Refraction Shorter Wavelength- waves speed slower Shallow water Deep water λ λ wavefront

Refraction If the incident wave travels at an angle and meets shallow water, then the wave will be refracted (shifted) towards the normal Angle of refraction Angle of incidence Normal line Shallow water Deep water Angle of incidence Angle of refraction >

Refraction What do you think will happen when a wave travels into deeper water? Draw a diagram with labels to represent the situation.