2.18 understand that: voltage is the energy transferred per unit charge passed, the volt is a joule per coulomb

Voltage is the energy transferred per unit charge passed, it is measures in volts. One volt is one joule per coulomb.

2.17 know that electric current in solid metallic conductors is a flow of negatively charged electrons

Electric current is the rate of flow of electrical charge (in amperes, A) around a circuit, in solid metal conductors (for example, a copper wire), charge is carried by negatively charged electrons.

2.16 know and use the relationship between charge, current and time.

Charge = current x time
    Q     =     I      x    t

Example...
A battery charger passes a current of 2.5A over a cell for a period of 4 hours. How much charge does the charger transfer to the cell altogether?

Firstly, cover 4 hours into seconds... 4 x 60 x 60 = 14,400 seconds.

now substitute into the equation...

Charge = 2.5 x 14,400 = 36,000 C (36 kC)

(charge is measured in coulombs, C)



Random fact that we need to know but doesn't really fit anywhere: the bigger the current the bigger the charge

2.15 understand that current is the rate of flow of charge

Charge cane positive or negative, and when it flows it is known as current. Therefore, current is the rate of flow of charge around a circuit, it will only flow through a component if there is a voltage across that component. The unit is Amps (or amperes), A.

2.14 know and use the relationship between voltage, resistance and current.

Voltage = current x resistance

V         =      I       x      R


Example..

a 4Ω resistor in a circuit has a voltage of 6V across it. What is the current through the resistor?


Firstly, rearrange the equation because we are finding I, the substitute what we know into it...

I = V/R

Therefore, Current = V/R = 6/4 = 1.5 A

Current = 1.5 A

2.13 know that lamps and LEDs can be used to indicate the presence of a current in a circuit

If there is a light in a circuit, it will be lit if there is a current in the circuit and not lit if there is no current. The same applies to LEDs (Light Emitting Diodes).

2.12 describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature

LDRs and Thermistors are components that can change their resistance (aka, it is not always the same).

An LDR (Light Dependant Resistor) changes its resistant depending on how much light falls on it. For example, in bright light the resistance is low and in darkness the resistance is at its highest.

A thermistor is a temperature-dependant resistor (its resistance changes depending on the temperature). For example, in hot conditions the resistance is low and in cooler conditions the resistance is high.

2.11 describe the qualitative effect of changing resistance on the current in a circuit

Increasing resistance (by adding components such as lamps or diodes) will decrease the current, decreasing resistance (removing components) will increase current.

2.10 describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how this can be investigated experimentally

Resistors (e.g lamps and diodes) lessen the flow of current, whilst voltage increases the current. This can be investigated using an ammeter (measures current) and a voltmeter (measures voltage).

Set up a circuit like this (known as the 'standard test circuit')...

Interchange the component with different resistors for example a lamp or diode, and record the recordings on the ammeter.

Also, increase/decrease the voltage and note the change on the ammeter.

Compare and contrast results. Overall, increasing the voltage should increase the number on the ammeter (current) whilst resistors (the components) will lower the current.

2.9 understand that the current in a series circuit depends on the applied voltage and the number and nature of other components

In a circuit, the voltage is the driving force.

Any component added into the circuit (for example, a lamp) will increase the amount of resistance in the circuit, this will decrease the current.

The voltage is trying to push the current around the circuit and the resistance is trying to slow it down, therefore, the relative sizes of the voltage and resistance decide how big the current will be.

If you increase the voltage - more current will flow
If you increase the resistance - less current will flow (alternatively, if you want the same amount of current to fly when the resistance is increased, you could increase the voltage).

2.8 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting

Series

In a series circuit, all components are connected on one line. This means that the voltage is shared between every component equally making it useful for supplying low power things, for example fairy lights. However, as the components are connected along one line, they can not be individually turned on, you can turn on all or none. Also, if one component breaks, the rest of the circuit will not work.

The circuit diagram above shows a circuit with two lamps connected in series. If one lamp breaks, the other lamp will not light.

Parallel

In a parallel circuit different components are connected separately to the supply. This means that, unlike in a series circuit, if one component breaks the other components can continue being powered as the whole circuit can still function. This makes it useful for powering objects that require a high power things as the voltage is equal throughout the circuit (therefore, each component receives the full voltage).

The circuit diagram above shows a circuit with two lamps connected in parallel. If one lamp breaks, the other lamp will still light.