y7 recap

• a switch needs to be closed to activate a circuit

• electrons (-)

• protons (+)

• neutrons (both)

• voltage is the amount of energy

• electricity is measured in volts

• electrons, protons and neutrons make up an atom, and they start to flow

• electricity is measured with an ammeter → flows of electrons

• conductors allow electrons to flow, but insulators dont

• current is measured in amps

basic electricity units

current (I) → rate of flow of charge (electrons)

unit → amps (A)

voltage (V) → the “push” that moves the electrons around the circuit, and is also known as the potential difference

unit → volts (V)

resistance

wires which have a higher resistance make electrons harder to pass through the atoms in the wire

resistance = voltage / current

R = V / I

unit of resistance = ohm = Ω

fuses

• safety feature in a circuit

• a thin short piece of wire with high resistance

• when heated up, melts and breaks the circuit if there is too much current

resistance calculation examples

circuit types

series circuit → where one component follows directly after another with no junctions and only has one loop

parallel circuit → different components are connected on different branches of the wire and has more than one loop

the resistance in series circuits is larger than in a parallel circuit, meaning that the bulbs are dimmer

flow of electrons

the current in a circuit depends on the voltage and the resistance

the current will be bigger if the resistance is smaller

inside a metal wire electrons collide with atoms and transfer energy to them

conductors are materials that contain lots of charges that are free to move

insulators contain fewer charges that can move

resistance in conductors is more than in insulators

magnetic and non-magnetic material

a non magnetic material is not attracted by a magnet

a magnetic material is attracted by a magnet

a magnet is either repelled or attracted by another magnet

iron (Fe), nickel (Ni), cobalt (Co) and steel are all magnetic

a domain is a collection of magnetic materials of individual electrons

in a magnetic material, the domains point in different directions until they are near a magnet. then they move and point in the direction of the magnet

in a magnet, all the domains always point in the same direction

non-magnetic materials dont have domains

making a magnet

to make a nail into a magnet, you can stroke it gently with a magnet.

when the nail is magnetised it is called an induced magnet (temporary magnet)

we can test the strength of the magnet by observing how many paperclips it can lift

with more strokes, the strength of the magnet will increase and it will be able to pick up more paperclips

electromagnets

an electromagnet is a type of magnet in within the magnetic field is produced by an electric current

the magnetic field around a wire which carries a current is in the form of circles

the direction of the field depends on the direction of the current

solenoids

to make a magnetic field stronger, rather than using just a single wire, a device called a Solenoid is used

a solenoid is a coil of wire with a current flowing through it

to make a magnetic field even stronger, a core made of magnetic material is placed inside the coil

by wrapping the wire in a coil, the magnetic fields add up to form a magnetic field like that of a bar magnet

it’s possible to increase the strength of a solenoid by increasing the current through the solenoid, introducing an iron core, or increasing the number of twists/coils of the wire on the solenoid

uses of electromagnets

applications of electromagnets

• lifting scrap cars

• the relay switch

• the motor

the relay switch is a special type of switch turned on and off by an electromagnet, and is used in items such as doorbells and starter motors in cars

1. when a current flows through a coil, an electromagnetic field is set up

2. the field attract an iron armature, whose other end pushes the contacts together, completing the circuit

3. when the current is switched off, the contacts open again, switching the circuit off