Transverse Waves The particles vibrate in the opposite direction that the energy is travelling

Longitudinal Waves

The particles vibrate in the same direction that the energy is travelling in

Frequency The frequency of a wave is how many waves that pass a point per second. The closer together the waves (or the shorter the wavelength), the higher the frequency. Frequency is measured in Hertz (Hz)

𝒔𝒑𝒆𝒆𝒅 = 𝒇𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 𝑯𝒛 × 𝒘𝒂𝒗𝒆𝒍𝒆𝒏𝒈𝒕𝒉 (′𝝀′ − 𝒊𝒏 𝒎𝒆𝒕𝒓𝒆𝒔)

• A peak is the tip of the wave, a trough is the bottom of a wave

• Wavelength is the length of one full wave – so from one peak to the next for example. Measured in metres (m)

• Amplitude is the height of the wave from the middle line. The greater the amplitude, the greater the energy of the wave

1. Transparent: A transparent object lets ALL of the light rays through, unchanged. A good example of a transparent object is a glass window. Transparent objects will not cast a shadow.

2. Translucent: A translucent object will let some of the light through, but the light rays are changed in some way. If you look through a translucent object what you see might be darker, blurred or a different colour. Translucent objects will cast a slight shadow.

3. Opaque: Opaque objects will not let any light through at all. They will absorb or reflect ALL of the light rays that hit them - you cannot see through an opaque object. Opaque objects will cast a darker shadow

Light is a type of energy that travels as a transverse wave. They travel in straight lines and are very fast, but their speed depends on what they are travelling through: In a vacuum (like space) it is 300,000,000 m/s! We can draw light using a ray diagram. We use a ruler to draw a straight line representing a ray of light, and we put an arrow on it to show the direction.

Shadows are caused when light rays hit an opaque or translucent object. The area behind the object looks darker because not all of the light rays have passed through the object

YEAR 8 WAVES LEARN SHEET: FOUNDATION TIER

Angle of incidence

THE LAW OF REFLECTION: “The angle of incidence IS THE SAME SIZE AS the angle of reflection”

REFLECTION

TIP:Make sure you can draw and label a diagram like this!

When a light ray travels from one type material into another type of material, it will change direction as follows: 1. If the light ray is going from air into water or glass, it will bend

towards the normal line. The angle of incidence will be bigger then the angle of refraction

2. If the light ray is going from water or glass into air, it will bend away from the normal line. The angle of incidence will be smaller then the angle of refraction

Angle of refraction

Refraction can make underwater objects appear to be in a different place than they are…

(the light ray going in)

(the light ray reflected out)

(A dotted line you draw on at right angles where the light ray hits the mirror)

REFRACTION: Light waves change direction

Light waves can have different wavelengths, our eyes see this as different colours!

Shining white light through a triangular prism at the right angle can separate the

different wavelengths (colours) of white light by refraction

A red apple appears red because it reflects the red wavelengths of light. These then go into our eye, and we see red. The apple absorbs all the other wavelengths / colours (these means they don’t get reflected)

Sound waves are longitudinal waves. Sounds are made when things vibrate. The vibrations are passed on by particles in solids, liquids or gases. Sound needs a substance to pass on the vibrations, so it can travel through solids, liquids and gases but not through a vacuum (like in space). The speed of sound is faster through solids than liquids, and slowest through gases. This is because the particles are very close together in solids and so the energy is more likely to be passed from one particle to the next.

Sound waves can be shown on an

oscilloscope. (see right)

The frequency of a wave is the number of vibrations each second. The unit for frequency is hertz (Hz). If you listen to a sound with a frequency of 100 Hz, one hundred waves reach your ear every second. High pitched sounds have a high frequency, and low pitched sounds have a low frequency. THE SPEED OF SOUND is about 330m/s in air. You can work out the speed of sound using the speed equation:

LOWEST FREQUENCY

HIGHEST FREQUENCY

The Electromagnetic (‘EM’) Spectrum

LEARN IT IN ORDER! 1. Radio waves 2. Microwaves 3. Infrared waves 4. Visible light 5. Ultraviolet 6. X-rays 7. Gamma rays

Radio waves 1 Have the longest wavelengths 2 Used in communications 3 Carry radio, TV, mobile phone signals 4 Highest frequency radio waves- • Carry more information • Have a shorter range

Microwaves Used in communication: can pass through atmosphere for satellite communications in space Used in cooking e.g microwave ovens which heat water molecules

Infrared-IR All objects emit IR. The hotter the object the more IR it emits IR waves heat objects. Uses: heaters, IR scanners, IR cameras, remote controls, optical fibres and communications

Visible light Optical fibres carry information e.g. internet. Other uses: photography, photocopying

X-Rays and Gamma Rays X rays are used in hospital to see broken bones. Gamma rays are used to sterilise equipment. Both types of wave damage living cells as they pass through. Large doses can kill cells. Smaller doses can cause cancer

Summary Questions: Y8 Waves Foundation Tier PAGE 1 1. Define a transverse and longitudinal wave. 2. Draw a labelled diagram of a transverse wave. 3. Define wavelength, frequency and amplitude. Give

units. 4. Calculate the speed of a wave with a frequency of 50Hz

and wavelength of 3m. 5. Give 2 examples each of transparent, translucent and

opaque objects. 6. What can happen to a light wave when it hits an object? 7. How is a shadow caused? 8. How would the shadow change if you moved the light

source closer to the object casting the shadow? PAGE 2 1. What is the law of reflection. 2. Study the reflection ray diagram on p2 for 1 minute.

Then try do draw it out from memory, fully labelled. Repeat until you can do it.

3. Define refraction and draw a ray diagram of a light ray passing through a glass block.

4. If a light ray travelled from water into air at an angle, would it bend towards the normal or away from the normal? Draw it.

PAGE 3 21. What is different about light waves of different colour? 22. Which colour has the largest wavelength and which the

shortest? 23. Complete the sentence: “White light is a mixture of…….” 24. What do white objects do well with light waves? 25. What do black objects do well with light waves? 26. How do our eyes see black objects? 27. Explain why a red apple in white light appears red. PAGE 4 21. What type of wave is a sound wave? 22. How do sound waves travel? 23. What materials can sound waves travel through? 24. Of these, what material does sound travel through the

fastest? 25. What can’t sound travel through and why? 26. What device can show you sound waves on a screen? 27. Draw what a loud, high pitched sound would look like on

this machine.

PAGE 5 21. Write out the components of the electromagnetic

spectrum in order of highest frequency to lowest frequency.

22. Describe some uses and risks of each component you have listed in Q19.