What does voltage mean, and how is it related to the energy given to charge?
Potential difference (voltage): voltage as the energy given to each unit of charge, the relationship between energy, charge and voltage, and how voltage behaves in series and parallel circuits.
An SQA National 5 Physics answer on potential difference, covering voltage as the energy transferred to each coulomb of charge, the relationship between energy, charge and voltage, how a cell provides voltage, and how voltage is shared in series circuits and the same across parallel branches.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this key area is asking
The SQA wants you to explain potential difference (voltage) as the energy given to each unit of charge, use the relationship between energy, charge and voltage, and state how voltage behaves in series and parallel circuits.
What voltage means
A cell gives of energy to every coulomb of charge that passes through it. The bigger the voltage, the more energy each coulomb carries, which is why a higher-voltage supply can light a lamp more brightly.
The energy, charge and voltage relationship
This relationship can be rearranged to find the energy transferred, , or the charge, . It is the formal definition of the volt: one volt is one joule per coulomb.
Voltage in series and parallel
This is the opposite pattern to current: in series the current is the same and the voltage is shared, while in parallel the voltage is the same and the current is shared. Knowing which pattern applies is a frequent source of marks, so learn the pair together.
How voltage and current differ
Voltage and current are easy to mix up but mean different things. Current is the flow of charge (how much charge passes each second), while voltage is the energy carried by each unit of charge. A voltmeter goes in parallel across a component because it measures the energy difference between two points; an ammeter goes in series because it measures the charge flowing through.
A useful way to picture voltage is to think of charge carrying energy around the circuit like buckets carrying water. The cell fills each bucket with energy (gives each coulomb a voltage), and as the charge passes through a lamp or resistor it empties its energy there, turning it into heat or light. The more energy each bucket carries, the bigger the voltage; the more buckets that pass each second, the bigger the current.
This is why a higher voltage makes a lamp brighter: each coulomb delivers more energy, so the lamp transfers energy faster. It also explains why the supply voltage in a series circuit is shared out, because the total energy given to each coulomb by the supply must all be transferred by the components it passes through before it returns to the cell.
Try this
Q1. State what one volt means in terms of energy and charge. [1 mark]
- Cue. One joule of energy transferred per coulomb of charge.
Q2. A charge of gains of energy. Calculate the voltage. [2 marks]
- Cue. .
Q3. State how the voltage behaves across each branch of a parallel circuit. [1 mark]
- Cue. It is the same as the supply voltage across every branch.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 style3 marksA battery transfers 24 J of energy to 4.0 C of charge. Calculate the potential difference (voltage) of the battery.Show worked answer →
Use the relationship between energy, charge and voltage.
Relationship: .
Substitution: .
Markers reward selecting the energy-per-charge relationship, correct substitution, and a final answer in volts ().
SQA N5 style3 marksIn a series circuit, a 12 V supply is connected to two identical lamps. The voltage across the first lamp is 7 V. State the voltage across the second lamp and explain your answer.Show worked answer →
In a series circuit the supply voltage is shared between the components, so the voltages across the components add up to the supply voltage.
Voltage across the second lamp .
The voltages do not have to be equal unless the components are identical and the question states the readings; here the data give on the first lamp, so the rest of the supply voltage, , is across the second.
Markers reward stating that series voltages add to the supply voltage and the correct value of .
Related dot points
- Electrical charge carriers: current as the flow of charge, the relationship between charge, current and time, the role of electrons as charge carriers, and how current divides in series and parallel circuits.
An SQA National 5 Physics answer on electrical charge carriers, covering current as the flow of charge, the relationship Q equals I times t, electrons as the charge carriers in a metal, the difference between conductors and insulators, and how current behaves in series and parallel circuits.
- Ohm's law: the relationship between voltage, current and resistance, the meaning of resistance, and calculating the total resistance of resistors in series and in parallel.
An SQA National 5 Physics answer on Ohm's law, covering the relationship V equals I times R, the meaning of resistance, how a V-I graph for a resistor is a straight line through the origin, and how to calculate the total resistance of resistors combined in series and in parallel.
- Practical electrical and electronic circuits: standard circuit symbols and components, input and output devices such as the LDR and thermistor, the potential divider, and the action of switches and simple control circuits.
An SQA National 5 Physics answer on practical electrical and electronic circuits, covering standard circuit symbols, input devices such as the LDR and thermistor and output devices such as the LED and motor, how a potential divider splits a voltage, and how these are combined into simple control circuits.
- Electrical power: power as energy transferred per second, the relationships linking power to current, voltage and resistance, and using power to find the energy and cost of running an appliance.
An SQA National 5 Physics answer on electrical power, covering power as energy per second, the relationships P equals I times V, P equals I squared R and P equals V squared over R, the link between power, energy and time, and how to work out the energy used and the cost of running an appliance.
Sources & how we know this
- SQA National 5 Physics Course Specification — SQA (2019)