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# Electricity and magnetism

Extracts from this document...

Introduction

## Electricity and magnetism

The charge is the amount of electricity in a circuit.

The symbol for charge is Q.

The unit for charge is coulombs.

A capacitor is a device that stores charge.

Charge = current x time.

• Most materials fall into two groups: conductors and insulators.
• A conductor allows electrons to flow through it.
• An insulator is a barrier to electricity.
• An insulator may act as a store of electricity known as static electricity.
• There is a small third group called semi conductors - these are used in electronics.
• The current is carried by ELECTRONS.
• Metals contain a "sea" of free electrons (negatively charged) which flow through the metal.
• This is what allows electric current to flow so well in all metals.
• Electric current will only flow if there are charges which can move freely (electrons).
• There are some things that you need to know for the exam about the difference between CONVENTIONAL and ELECTRICAL current.
• CONVENTIONAL current flows from POSITIVE TO NEGATIVE.
• ELECTRICAL current flows from NEGATIVE TO POSITIVE.
• So electrons flow opposite to the flow of conventional current.

CURRENT - is the flow of electrons round the circuit.

VOLTAGE

Middle

The bigger the resistance of a component, the bigger its share of voltage.

Static electricity

• There are two types of charge: + positive and - negative.
• An uncharged material has equal numbers of both so the material is balanced out.
• Friction between materials caused an exchange of charges.
• The negative charges move but positive stay where they are.
• Once a material is charged it will attract materials with the opposite charge and repel materials that have the same charge.
• An example of static electricity in industry is when painting cars. The car body is charged evenly and the paint is prayed on. The paint particles are attracted to the car and spread out because of the charge. This ensures the car is painted evenly.

## Forces and motion

• Forces are usually a push or a pull.
• Forces are measured using a newtonmeter and the unit of force is Newtons.
• Forces work in pairs - as you push down on a table the table pushes up with equal force.
• When there is no change in velocity or shape of an object then the forces are balanced e.g. book on table

Conclusion

Sun tanningVisable light. Human sightInfrared. Cooking (heat)Microwaves. CookingRadio waves. Communication

Light
The primary light colours are red blue and green. They can be mixed, as follows, to form secondary light colours:
red + green = yellow
red + blue = magenta
blue + green = cyan

By using a prism, white light can be separated into all the different (dispersion) colours that make up white light. These are (starting with long wavelength):
red, orange, yellow, green, blue, indigo, violet

Reflection:
The angle of incident always equals the angle of reflection. These are measured against the normal which is an imaginary straight line at a right angle to the mirror.

Refraction:
Refraction is the process that occurs when light travels from one material to another, it is either speed up or slowed down. This has an effect on the light and bends it. The denser the material, the slower the speed of light.

Sound
Sound waves are caused by vibrations in the air. They cannot travel through vacuums. The denser the material, the faster sound can travel.

Sound waves are reflected and this is heard by us as an echo. The echo is the sound being reflected - just like light reflected from a mirror.

Ultrasound has a very high frequency and we canv not hear it but bats use it to fly and it is also used to look inside the body.

This student written piece of work is one of many that can be found in our AS and A Level Fields & Forces section.

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