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

Longitudinal Waves The particles vibrate/oscillate 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 100% of the light rays straight through, unchanged. We say the light rays have been ‘transmitted’ through the object. A good example of a transparent object is a glass window. Transparent objects will not cast a shadow.

2. Translucent: A translucent object will transmit some of the light, but the light rays are changed in some way: Some of the light rays may be absorbed, and/or reflected. Because of this, if you look through a translucent object what you see might appear darker, blurred and/or a different colour. Translucent objects will cast a slight shadow.

3. Opaque: Opaque objects will not transmit any light at all. They will absorb or reflect 100% 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! It is slower in air though. In fact, the more dense the substance is, the slower light will travel through it. When light rays hit an object they can be: a) transmitted b) reflected c) refracted d) absorbed 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

FINAL POINT for page 1: ‘LUMINOUS’ objects give off their own light (like a light bulb) and ‘NON-LUMINOUS’ objects don’t. We only see non-luminous things because light rays (from luminous objects) bounce off them into ours eyes!

Angle of incidence

THE LAW OF REFLECTION: “Angle of incidence = angle of reflection”

REFLECTION

plane mirror

Incident ray

The image that is formed in a plane mirror: a) is virtual (ie isn’t real). b) is upright. c) is the same shape and size as the object it is reflecting. d) appears to be the same distance ‘behind’ the mirror as the

object is in front.

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

Diamond Glass Water Air Vacuum (space)

LEAST DENSE

MOST DENSE

When a light ray travels from one material into another material at an angle, it will change direction as follows: a) If the light ray is entering a more dense

material, it will bend towards the normal line. The angle of incidence will be bigger then the angle of refraction (i1>r1)

b) If the light ray is entering a less dense material, it will bend away from the normal line. The angle of incidence will be smaller then the angle of refraction (i2<r2)

Angle of refraction

cladding inner core

normal

Total internal reflection at the boundaries

When you shine a light ray at the boundary between one substance and another, and you pass a ‘critical angle’, then the light ray will stop refracting and will reflect instead. This is called TOTAL INTERNAL REFLECTION

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

An important use of total internal reflection is with optical fibres. Optical fibres use light to send information (like video/audio/internet data) at extremely fast speeds!

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

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. The sound travels in all directions because the particles move in all directions unless something stops them.

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:

Ultrasound is the name given to sound waves that have frequencies greater than 20000Hz. It's too high pitched for human hearing, but many animals, such as dogs, cats and bats can hear ultrasound. Humans use ultrasound machines for many things. One of the most well known is to check the condition of a foetus (unborn baby in the womb) The ultrasound waves reflect off the foetus and a computer sensor detects the echoes and can build a picture from it!

Bats use ‘echolocation’ to find prey –they give off pulses of ultrasound And they detect the echoes as the sound waves reflect off small insects

An echo is a reflected sound wave. Humans and animals make use of echoes in different ways

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

Ocean Depth Sound travels at 1500 m/s in seawater. Ships send a pulse of sound and time how long it takes for the echo to return This is twice the depth of the sea (the sound wave went down and back again)

To find the depth they use the speed equation: Distance = speed x time BUT they need to divide the time they measured in half because the sound went to the bottom and back, so took twice as long!

Summary Questions 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. What is the relationship between wavelength and frequency? 5. Calculate the speed of a wave with a frequency of 50Hz and

wavelength of 3m. 6. What is the wavelength of a wave with a speed of 330m/s and a

frequency of 11Hz? 7. What is the difference between luminous and non luminous

objects? 8. Give 2 examples each of transparent, translucent and opaque

objects. 9. What can happen to a light wave when it hits an object? 10. How is a shadow caused? 11. How would the shadow change if you moved the light source

closer to the object casting the shadow? 12. What is the law of reflection. 13. 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.

14. What are the features of an image formed in a plane mirror? 15. A man stands in front of a mirror. Draw a diagram showing how

the virtual image is formed in the mirror. 16. Define refraction and draw a ray diagram of a light ray passing

through a glass block. 17. If a light ray travelled from glass into diamond at an angle,

would it bend towards the normal or away from the normal? 18. What is the ‘critical angle’? 19. Define total internal reflection and give 1 use of it. 20. What is different about light waves of different colour?

21. Which colour has the largest wavelength and which the shortest?

22. Complete the sentence: “White light is a mixture of…….” 23. What do white objects do well with light waves? 24. What do black objects do well with light waves? 25. How do our eyes see black objects? 26. Explain why a red apple in white light appears red. 27. What colour would a red apple in blue light appear? Explain your

answer (use a diagram if you wish). 28. What type of wave is a sound wave? 29. How do sound waves travel? 30. What materials can sound waves travel through? 31. Of these, what material does sound travel through the fastest? 32. What can’t sound travel through and why? 33. What device can show you sound waves on a screen? 34. Draw what a loud, high pitched sound would look like on this

machine. 35. What is the link between the amplitude, wavelength and

frequency of a sound wave, and the pitch and volume of the sound?

36. What is an echo? 37. Describe some examples of how echoes are used by humans and

by animals. 38. Write out the components of the electromagnetic spectrum in

order of highest frequency to lowest frequency. 39. Describe some uses and risks of each component you have listed

in Q19. 40. How can you calculate the speed of a sound wave? 41. A ship used ultrasound to scan the depth of the ocean. The pulse

of sound took 60 seconds to be detected by the receiver on the ship. How deep was the ocean?