Unit 1 Topic 3 - Electrical circuits

Charge

A physical property of an object that causes it to experience a force when placed in an electromagnetic field. It is measured in coulombs (c) with the unit symbol Q.

Electrical field

The region around an electrically charged particle within which a force would be exerted on other electrically charged particles or objects. It is measured in newtons per coulomb (N/C), with the symbol E ⃗.

Law of conservation of charge

The total electric charge of an isolated system remains constant regardless of changes within the system.

Current

The rate of movement of electric charge carriers through a circuit. It is measured in amperes (A) and has the symbol I.

Conventional current

The flow of positive charge from a positive terminal to a negative terminal in an electric circuit, regardless of the actual direction of electron movement.

Electrical circuit

The simplest consists of a source of electric potential energy in the form of an EMF, connecting wires and an element that provides resistance or load.

Ammeter

A device that sits in series with a circuit and measures the current flowing through it. They are said to have no resistance.

Series circuit

A circuit in which all the elements are connected end to end in one continuous loop.

Parallel circuit

A circuit that features multiple paths/branches of wires for electrons to flow through.

Potential difference

The change in potential energy or the work done per unit of charge between two defined points in a circuit. It is measured in voltage (V) and denoted by ΔV.

Direct potential difference

A specific type of electrical potential difference that does not change its polarity over time.

Voltmeter

A device that sits in parallel to a circuit, measuring the potential difference between two points of connection. It is often used to measure the energy consumed by a device and is said to have infinite resistance.

Ohm's law (proportionality)

The potential difference across a metallic conductor, v, and the current flowing through it, I, are directly proportional at a given temperature. This is measured through the formula V = IR.

Resistance

A measure of how much a material tries to stop electricity from passing through it by opposing the flow of conventional current.

Factors affecting resistance

The longer a resistor is and the smaller it’s cross-sectional area is, the more resistance, with certain materials having higher resistivity than others.

Ohmic resistor

A device that maintains a stable resistance, and when connected to a circuit, will behave according to Ohm's law.

Non-ohmic resistor

A device that does not behave according to Ohm's law, and is neither linear nor directly proportional.

Variable resistor

A resistor that can vary its resistance, often referred to as potentiometers or voltage dividers.

Carbon resistors

A type of resistor in which all resistors with a power rating up to one watt are marked with colour bands, with each colour corresponding to a different resistance.

Power

The amount of energy consumed per second by a device.

Power rating

The maximum power a device can safely use/deliver without sustaining damage.

Power dissipation

The conversion of electrical energy into heat within a circuit, caused by current flowing through components with resistance.

Kirchhoff's current law

At any node or junction in an electrical circuit, charge is conserved such that the sum of electrical charge flowing into a node is equal to the sum of electrical charge flowing out of that node.

Kirchhoff's voltage law

The energy input in a circuit is equal to the sum of energy outputs from elements in the circuit, such that the directed sum of electrical potential difference around any closed circuit is zero.

Current (parallel vs series)

Current is the same across a series circuit, and is shared across a parallel circuit.

Voltage (parallel vs series)

Voltage is shared across a series circuit, and is the same across a parallel circuit.

Current formula

I = Q/t, where I is the current in amps (A), Q is the charge in coulombs (C), and t is time in seconds (s).

Coulombs

The unit of measurement for charge, with a total of 6.24 * 10^18 electrons.

Voltage formula

V = W/Q, where V is the voltage, W is the work done in joules and Q is the charge in coulombs.

Ohm's law (formula)

V = IR, where V is potential difference in volts, I is current in amps and R is resistance in ohms.

Efficiency

Useful energy/total energy * 100%.

Power formulas

P = VI, P = W/t and P = I^2R.

Total resistance

Rt = R1 + R2 + R3

Parallel resistance

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