GCSE Physics Revision: Electricity notes

Electric Charge

Electric charge is a fundamental property of matter. There are two types of electric charge: positive and negative. Objects with the same charge repel each other, while objects with opposite charges attract each other.

The unit of electric charge is the coulomb (C).

Electric Current

Electric current is the flow of electric charge through a conductor. The unit of electric current is the ampere (A).

Electric current can be either direct current (DC) or alternating current (AC).

Voltage

Voltage is the difference in electric potential energy between two points in an electric circuit. The unit of voltage is the volt (V).

The voltage across a component in a circuit can be calculated using Ohm's law:

V = IR

where V is the voltage, I is the electric current, and R is the resistance of the component.

Resistance

Resistance is a measure of how much a component resists the flow of electric current. The unit of resistance is the ohm (Ω).

The resistance of a component can be calculated using Ohm's law:

R = V/I

where R is the resistance, V is the voltage, and I is the electric current.

Series and Parallel Circuits

Components in a circuit can be connected in series or parallel. In a series circuit, the components are connected in a single path, so the same current flows through each component. In a parallel circuit, the components are connected in separate paths, so the current is divided between them.

The total resistance of components in a series circuit can be calculated by adding their individual resistances:

RT = R1 + R2 + R3 + ...

The total resistance of components in a parallel circuit can be calculated using the equation:

1/RT = 1/R1 + 1/R2 + 1/R3 + ...

Mains Electricity

Mains electricity is the alternating current (AC) that is supplied to homes and businesses through power lines. The standard voltage and frequency of mains electricity varies by country.

Mains electricity can be dangerous and should be handled with care. Safety measures, such as fuses and circuit breakers, are used to protect against electrical hazards.

Circuit breakers are similar to fuses in that they are designed to protect against overloading and short circuits. However, instead of containing a wire or element that will melt, circuit breakers contain a switch that will automatically trip if the current in the circuit exceeds a certain level. Once the switch has tripped, the circuit will be broken, and the current will stop flowing. Circuit breakers are typically used in higher-voltage circuits, such as those found in buildings and industrial settings.

Earthing is another safety measure that is used to protect against electric shocks. Earthing involves connecting the metal frame of an electrical device to the ground. If there is a fault in the device that causes the metal frame to become live, the current will flow through the earth connection instead of through a person who touches the metal frame. This can prevent serious injury or even death.

Electric Components

There are several types of electric components that are commonly used in circuits, including:

  • Lamps: Lamps convert electrical energy into light energy.
  • Fuses: Fuses are used to protect against overloading and overheating in a circuit.
  • Resistors: Resistors are used to control the flow of electric current in a circuit.
  • Thermistors: Thermistors are temperature-sensitive resistors that are used in temperature-sensing applications.
  • LDRs: Light-dependent resistors (LDRs) are used in light-sensing applications.
  • Diodes: Diodes are used to control the flow of electric current in a circuit.

Equations

There are several key equations that are used in electricity:

  • Ohm's law: V = IR, where V is the voltage, I is the electric current, and R is the resistance of the component.
  • Resistance: R = V/I, where R is the resistance, V is the voltage, and I is the electric current.
  • Power: P = IV, where P is the power, I is the electric current, and V is the voltage.
  • Energy: E = Pt, where E is the energy, P is the power, and t is the time.

    • Static Electricity

    Static electricity is the buildup of electric charge on the surface of an object. This can happen when two materials are rubbed together, causing electrons to be transferred from one material to the other. The material that gains electrons becomes negatively charged, while the material that loses electrons becomes positively charged.

    Static electricity can also be created by induction. This happens when a charged object is brought near a neutral object, causing electrons to be either attracted or repelled from the neutral object. This results in a separation of charges, with one side of the object becoming positively charged and the other side becoming negatively charged.

    Static electricity is used for appliances such as a laser printer and can be dangerous in certain situations, such as when refueling a car or an aircraft.