Summary of Basic Circuit Knowledge

ammeter
cells in series
characteristic curves
circuit symbols
current
diode
equations
Kirchhoff's First Law
ohmmeter
Ohm's Law
parallel circuits
potential difference
power
resistances in parallel
resistances in series
series circuits
voltmeter

When an electric current flows through a circuit, energy is transferred from the battery or power supply to the components in the electrical circuit.

An electric current is a flow of charge.

A current will flow through an electrical component (or device) only if:

there is a voltage or potential difference (p.d.) across its ends. The bigger the potential difference across a component, the bigger the current that flows through it.

It is part of a complete circuit. If there is a gap in the circuit then the whole strand that the gap is in will not have current flow through it.

Measuring Instuments

The p.d. across a component in a circuit is measured in volts (V) using a voltmeterconnected across (in parallel with) the component.

 

The current flowing through a component in a circuit is measured in amperes (A) using an ammeterconnected in series with the component.

 

An ohmmeter measures the resistance of a component in ohms (Ω). The component should not be in a circuit when measured - or if it is fixed within a circuit you need to make sure there is no power applied to that circuit. An ohmmeter is connected across (in parallel with) the component.

 

Equations you should know how to use:

Potential difference, current and resistance are related as shown in Ohm's Law:

V = I R

Where: V= potential difference (in volts, V)
I = current (in ampere, A)
R = resistance (in ohm, Ω)

Current-voltage graphs are used to show how the current through a component varies with the voltage you put across it. These are called Characteristic Curves (Click here).

When electrical charge flows through a resistor, electrical energy is transferred as heat.
The rate of energy transfer (power) is given by:

P = IV
Where: P = power (in watts, W)
V = potential difference (in volts, V)
I = current (in ampere, A)

1W (one watt) is the transfer of 1J (one joule) of energy in 1s (one second).

The higher the voltage of a supply, the greater the amount of energy transferred for a given amount of charge which flows.

E = VQ
Where E = energy transferred (in joule, J)
V= potential difference (in volt, V)
Q = charge (coulomb, C)

The amount of electrical charge which flows is related to current and time as follows:

Q = It
Where: Q = charge (coulomb, C)
< class="answer">I = current (in ampere, A)
t = time (in seconds, s)

The total amount of energy  transferred by an electrical device can be calculated as follows:

E = Pt
Where E = energy transferred (in joule, J)
P = power (in watts, W)
t = time (in seconds, s)

Domestic Electrical Appliances - click here

 

Circuit Symbols - click here