P6 The Wave Model of Radiation Introduction Source of much of the information and diagrams: http://www.gcse.com/waves.htm

Waves A wave is a disturbance moving through a material. It transfers energy in the direction that the wave travels, without transferring matter. What is different about these two sorts of wave? Transverse wave Longitudinal wave

A wave is a disturbance moving through a material.

It transfers energy in the direction that the wave travels, without transferring matter.

From KS3 What is a source (of waves)? What is a medium? What is a vacuum?

What is a source (of waves)?

What is a medium?

What is a vacuum?

From KS3 What is a source (of waves)? – something that vibrates What is a medium? -the material that the wave travels through What is a vacuum? - the absence of matter

What is a source (of waves)?

– something that vibrates

What is a medium?

-the material that the wave travels through

What is a vacuum?

- the absence of matter

Transverse Waves The oscillations are at 90° to the wave motion: One way of remembering this is that is looks like an s on its side. Transverse has two s's in it, longitudinal has none.

The oscillations are at 90° to the wave motion:

Most waves are transverse: all electromagnetic waves i.e. radio, micro, infra red, light, ultra violet, X-rays and gamma waves water waves - ripples on the surface of a sea or lake S Waves - a type of earthquake wave

all electromagnetic waves i.e. radio, micro, infra red, light, ultra violet, X-rays and gamma waves

water waves - ripples on the surface of a sea or lake

S Waves - a type of earthquake wave

Longitudinal Waves The oscillations are in the direction of wave motion. E.g. sound, ultrasound and earthquake P-waves.

The oscillations are in the direction of wave motion.

E.g. sound, ultrasound and earthquake P-waves.

Wavelength The length of a complete wave (in metres) The biggest mistake most people make is with drawing this on a picture of a transverse wave. Draw a complete wave length - from the same point on each wave ripple:

The length of a complete wave (in metres)

The biggest mistake most people make is with drawing this on a picture of a transverse wave.

Draw a complete wave length - from the same point on each wave ripple:

Wavelength Wavelength is the distance between parts of the wave that are doing the same thing .

Wavelength is the distance between parts of the wave that are doing the same thing .

Amplitude (For water waves/rope/spring) The maximum distance that each point in the medium moves from its normal position as the wave passes. (measured in metres)

(For water waves/rope/spring)

The maximum distance that each point in the medium moves from its normal position as the wave passes.

(measured in metres)

Amplitude (For water waves/rope/spring) The maximum distance that each point in the medium moves from its normal position as the wave passes. (measured in metres)

(For water waves/rope/spring)

The maximum distance that each point in the medium moves from its normal position as the wave passes.

(measured in metres)

Amplitude All waves involve an oscillation of some kind. This means that something is pulled away from an equilibrium position, moves back, then through the other side. We call the amount of movement from equilibrium displacement. Amplitude is just the maximum displacement of a wave:

All waves involve an oscillation of some kind. This means that something is pulled away from an equilibrium position, moves back, then through the other side.

We call the amount of movement from equilibrium displacement.

Amplitude is just the maximum displacement of a wave:

Amplitude is defined as the maximum displacement from the rest position . In other words, the furthest distance something moves from where it was at rest. Looking at the snapshot below of part of a longitudinal motion. At the top, the red line is at its rest position . Underneath is the red line shown at its maximum displacement to the right. The distance it has moved is the amplitude of the oscillation.

Amplitude is defined as the maximum displacement from the rest position .

In other words, the furthest distance something moves from where it was at rest.

Looking at the snapshot below of part of a longitudinal motion. At the top, the red line is at its rest position .

Frequency The number of waves that pass any point in the medium every second. = number vibrations per second Measured in hertz (Hz) 1 Hz = 1 wave per second

The number of waves that pass any point in the medium every second.

= number vibrations per second

Measured in hertz (Hz)

1 Hz = 1 wave per second

Frequency in hertz Like any unit, we can add prefixes in front of it to make alternatives: e.g. 1 kilohertz = 1 kHz = 1,000 Hz 1 megahertz = 1 MHz = 1,000,000 Hz 1 gigahertz = 1 GHz = 1,000,000,000 Hz You will no doubt be using a computer that has a speed of many mega-hertz, or even giga-hertz! Historical note: hertz is named after the German physicist, Heinrich Hertz (d. 1967)

Like any unit, we can add prefixes in front of it to make alternatives:

e.g. 1 kilohertz = 1 kHz = 1,000 Hz 1 megahertz = 1 MHz = 1,000,000 Hz 1 gigahertz = 1 GHz = 1,000,000,000 Hz

You will no doubt be using a computer that has a speed of many mega-hertz, or even giga-hertz!

Historical note: hertz is named after the German physicist, Heinrich Hertz (d. 1967)

Speed, frequency and wavelength The frequency of a set of waves is set at the source itself. For instance, if Billy pokes a pond with a stick twice each second, the frequency will be 2 Hz. As the waves travel over the pond's surface, this frequency will not change. What may change is the distance between waves - the wavelength - and their speed.

The frequency of a set of waves is set at the source itself.

For instance, if Billy pokes a pond with a stick twice each second, the frequency will be 2 Hz.

As the waves travel over the pond's surface, this frequency will not change. What may change is the distance between waves - the wavelength - and their speed.

Isobel sets up a ripple tank to produce 2 waves each second (i.e. frequency = 2 Hz). She times the waves 2 s to travel the 100 cm distance to the other side of the tank. She measures the distance between the waves as 25 cm: this is the wavelength. A frequency of 2 Hz means one wave is produced every 0.5 s (this is known as the time period of the waves and is 1÷frequency). In 0.5 s, waves move 25 cm, so we can find the speed using:

Isobel sets up a ripple tank to produce 2 waves each second (i.e. frequency = 2 Hz).

She times the waves 2 s to travel the 100 cm distance to the other side of the tank. She measures the distance between the waves as 25 cm: this is the wavelength.

A frequency of 2 Hz means one wave is produced every 0.5 s (this is known as the time period of the waves and is 1÷frequency).

In 0.5 s, waves move 25 cm, so we can find the speed using:

We can check the speed found using the length of the tank and the time taken: So the relationship between speed, frequency and wavelength is: Incidentally, the funny upside-down y is a greek letter called "lamda". You may need to know this formula!

We can check the speed found using the length of the tank and the time taken:

So the relationship between speed, frequency and wavelength is:

Incidentally, the funny upside-down y is a greek letter called "lamda". You may need to know this formula!

Speed = Frequency × Wavelength Bill counts 5 waves on a pond in 10 s. The distance between them is 80 cm. What is their speed? Lizi reads the back label of her microwave oven. It says frequency = 2,450 MHz. The speed of microwaves is 3.00×108 m/s. What wavelength are they? Paul plays a note of wavelength 25 cm on his synthesiser. He knows the speed of sound is 340 m/s in air. What is its frequency?

Bill counts 5 waves on a pond in 10 s. The distance between them is 80 cm. What is their speed?

Lizi reads the back label of her microwave oven. It says frequency = 2,450 MHz. The speed of microwaves is 3.00×108 m/s. What wavelength are they?

Paul plays a note of wavelength 25 cm on his synthesiser. He knows the speed of sound is 340 m/s in air. What is its frequency?

Solutions 5 waves in 10 s. Distance between is 80 cm. Speed? frequency = 5/10 = 0·5 Hz. speed = frequency × wavelength = 0·5 × 80 = 40 cm/s frequency = 2,450 MHz. speed = 3.00×108 m/s. speed = frequency × wavelength 3.00×108 = 2,450×106 × wavelength wavelength = 3.00×108 ÷ 2,450×106 = 0·122 m = 12·2 cm wavelength= 25 cm = 0·25 m. Speed = 340 m/s speed = frequency × wavelength 340 = frequency × 0·25 frequency = 340 ÷ 0·25 = 1,360 Hz

5 waves in 10 s. Distance between is 80 cm. Speed? frequency = 5/10 = 0·5 Hz. speed = frequency × wavelength = 0·5 × 80 = 40 cm/s

frequency = 2,450 MHz. speed = 3.00×108 m/s. speed = frequency × wavelength 3.00×108 = 2,450×106 × wavelength wavelength = 3.00×108 ÷ 2,450×106 = 0·122 m = 12·2 cm

wavelength= 25 cm = 0·25 m. Speed = 340 m/s speed = frequency × wavelength 340 = frequency × 0·25 frequency = 340 ÷ 0·25 = 1,360 Hz

Waves Summary Waves all transfer energy from one place to another. They do this by vibrating something. There are two types of waves: longitudinal and transverse. Most waves are transverse. Longitudinal waves have vibrations in the same direction as the wave motion. Transverse wave vibrations are at 90° to the direction of the wave.

Waves all transfer energy from one place to another. They do this by vibrating something.

There are two types of waves: longitudinal and transverse. Most waves are transverse.

Longitudinal waves have vibrations in the same direction as the wave motion.

Transverse wave vibrations are at 90° to the direction of the wave.

Waves Summary Wavelength is the distance from one part of a wave and the same point on the next wave along. e.g. peak to peak. Amplitude is the maximum movement from the original position. For transverse waves this is the height of the wave from the middle. Frequency is the number of waves per second and it is measured in hertz (Hz). The speed of a wave can be found by using this formula: m/s = Hz x m

Wavelength is the distance from one part of a wave and the same point on the next wave along. e.g. peak to peak.

Amplitude is the maximum movement from the original position. For transverse waves this is the height of the wave from the middle.

Frequency is the number of waves per second and it is measured in hertz (Hz).

The speed of a wave can be found by using this formula: