Physics current electricity

• Insulation

• Double insulation

• EARTHING

• Fuses

• Circuit breakers

Wires are insulated with plastic, to prevent an electric shock occurring when the user touches it

The appliance is completely covered in a layer of an insulating material, e.g. plastic, which means that there is no possibility of a current passing through to the user. This is usually used instead of an earth wire.

In addition to the (brown) live wire (that carries the current into the appliance), and the (blue) neutral wire (that carries the current out of the appliance) the (green and yellow) earth wire provides a path of very low resistance to the ground, so electrical energy flows through it rather than through the user.

The fuse is connected to the live wire. The value of the fuse must be slightly higher that what the appliance needs to function. When the current is too high, the fuse melts, breaking the circuit and protecting the appliance and user.

Circuit breakers are resettable fuses. If the current exceeds a certain value, an electromagnet will separate a pair of contacts, breaking the circuit. They are more practical than fuses.

The temperature increases, as a result of the electrons (that are flowing through the conductor as current) colliding with ions in the lattice and transferring some of their energy to these ions, which then vibrate more, causing the resistor to heat up. This is used in toasters, kettles, electric heaters, ovens.

Ions in a lattice resist the flow of electrons

Power = current x voltage (P=IV)

Energy transferred = current x voltage x time (E=VIT)

Alternating current: current first flows one way, then the opposite way. Used to supply mains electricity.

Direct current: current only flows one way. Used to supply current in cells and batteries.

The current is the same throughout the entire circuit. As voltage increases, current increases. If there are more components in the circuit, current decreases, as there is more resistance.

Current is shared between branches; current at source = sum of current in each brach

Voltage is shared across the whole circuit; voltage at power supply = sum of voltage across each component

Voltage is the same across each branch; voltage at power supply = voltage at each branch

Total resistance = sum of resistance of each component. This is why more components increase resistance, therefore decreasing current.

Increasing resistance decreases current

As light intensity increases, resistance decreases.

As temperature increases, resistance decreases

Voltage = current x resistance (V=IR)

Current is the rate of the flow of charge (measured in Amperes)

Charge = current x time (Q=IT - we need to QUIT physics)

The flow of (negatively charged) electrons

It is conserved - the current flowing into the junction is equal to the current flowing out of it, because current is the flow of electrons, and these cannot be created or destroyed, so the number of electrons flowing in the circuit must remain the same. This does not mean that the current will split equally along two branches - this depends on the resistance in each branch.

Voltage is energy transferred per unit charge. This means that one volt is a joule per coulomb.

Energy transferred = charge x voltage (E=QV)

Directly proportional (goes through negative as well)

A diode is a component that only allows current to flow one way

Flattening curve, opposite in the negative axis

The metal ions vibrate more when temperature increases. This means that there is a greater chance of electrons colliding with them, making it harder for current to flow through, so the resistance increases.