 # 3 Waves – Part A “Units”

### Aims…

3.1 use the following units: degree (o), hertz (Hz), metre (m), metre/second (m/s), second (s).

### General Ideas…

A physical quantity is something that can be measured. For any measurement, the unit being used must be stated to give an understanding of the scale of the measurement.

For example, distance can be measured in kilometres or in miles. They are similar, but not the same and it is important to identify which was used for the measurement, to know how far the distance actually is.

Système Internationale d’Unités

The units that scientists use all over the world are standardised in the Système Internationale d’Unités – SI units. It is important to remember these six fundamental (or ‘base’) units of measurement:

There are many quantities scientists measure that come from the base units. These derived units are very useful to quote as measurements, but they are not fundamental as they come from fundamental units.

For example, frequency is the number of times something happens per unit of time.

This is a useful quantity, but it is a division into the time unit.

The standard unit for frequency is considering the number ‘per second‘, which is called ‘hertz, Hz’, but this comes from the fundamental unit ‘second‘.

 Name Unit Abbreviation Frequency hertz Hz Force newton N Energy joule J Power watt W Pressure pascal Pa Electric charge coulomb C Work Done or Work Nm or J W Gravity or acceleration Nkg-1ms-2 g or a Momentum kgms-1 p

Kilogram (kg): the SI unit of mass, equivalent to the international standard kept at Sèvres near Paris (approximately 2.205 lb).

Metre (m): the fundamental unit of length in the metric system, equal to 100 centimetres or approximately 39.37 inches.

Second (s): the SI base unit of time which is used to determine progression of the universe. Defined from a complex atomic transition or as a division of an Earth day.

Degree (°): this is a way to measure an angle. With 360° in a circle (same as 2p radians) we can use this to measure angles from the normal from a surface to explain wave behaviours

Speed: the rate at which someone or something moves or operates or is able to move or operate in m/s or ms-1

Frequency:  This is a useful quantity, but it is a division into the time unit. The standard unit for frequency is considering the number ‘per second‘, which is called ‘hertz, Hz’, but this comes from the fundamental unit ‘second‘.

Period: T or time for 1 whole cycle of a wave measured in s or hours etc..

### Resources….

Use this PowerPoint for a quick review… 3 Waves Part A Units

## 3 Waves – Part B “Properties of Waves”

Syllabus Aims…
3.3 know the definitions of amplitude, wavefront, frequency, wavelength and period of a wave
3.4 know that waves transfer energy and information without transferring matter
3.5 know and use the relationship between the speed, frequency and wavelength of a wave:
wave speed = frequency × wavelength
v = f × λ
3.6 use the relationship between frequency and time …

## 3 Waves – Part C “Electromagnetic Spectrum”

Syllabus Aims…
3.10 know that light is part of a continuous electromagnetic spectrum which includes: radio, microwave, infrared, visible, ultraviolet, X-ray and gamma ray radiations and that all these waves travel at the same speed in free space
3.11 know the order of the electromagnetic spectrum in terms of decreasing wavelength and increasing frequency, including the colours …

## 3 Waves – Part D1 “Light”

Syllabus Aims…
3.14 know that light waves are transverse waves which can be reflected, refracted
3.15 use the law of reflection (the angle of incidence equals the angle of reflection)
3.16 draw ray diagrams to illustrate reflection and refraction.
3.17 practical: investigate the refraction of light, using rectangular blocks, semicircular blocks and triangular prisms
3.18 know and use the relationship …

## 3 Waves – Part D2 “Sound” – Triple

Syllabus Aims…
3.24P understand that the frequency range for human hearing is 20 Hz – 20 000 Hz
3.25P investigate the speed of sound in air.
3.26P understand how an oscilloscope and microphone can be used to display a sound wave
3.27P practical: investigate the frequency of a sound wave using an oscilloscope
3.28P understand how the pitch of a sound …

## Human Eye

This simple animation contains drag and drop games and scroller windows to show some of the features of the Human Eye it is suitable for all levels…

## Infra Red Waves & Remote Controls..

Most remote controls for electronic appliances use a near infrared diode to emit a beam of light that reaches the device. A 940 nm wavelength LED is typical. This infrared light is invisible to the human eye, but picked up by sensors on the receiving device. Video cameras see the diode as if it produces …