Electricity and Circuits for Singapore N(A)-Level Science (Physics) 5105/5106: static electricity and electric current as the flow of charge, voltage, resistance and Ohm's law with electrical power, and how current and voltage behave in series and parallel circuits

What this module covers

Electricity and Circuits explains how charge flows and how we control it in N(A)-Level Science (Physics) 5105/5106. It starts with static electricity, where charge builds up but does not flow, and moves to current, the steady flow of charge round a circuit. It then defines the two quantities that govern circuits, voltage and resistance, links them through Ohm's law, and shows how current and voltage behave when components are joined in series or in parallel.

These ideas explain everything from a shock off a doorknob to the wiring of a home, and they connect to the energy module through electrical power. Each dot point below has full worked answers and practice questions.

Static electricity and current

Static electricity and current explains how objects gain charge by friction, which transfers electrons from one surface to another. Like charges repel and unlike charges attract. When charge flows steadily round a circuit it is an electric current, the rate of flow of charge, given by

Voltage, resistance and Ohm's law

Voltage, resistance and Ohm's law defines voltage as the energy given to each unit of charge and resistance as the opposition to current. Ohm's law links them:

Electrical power, the rate of transfer of electrical energy, is

Series and parallel circuits

Series and parallel circuits compares the two ways of joining components. In series there is one path: the current is the same everywhere, the voltages add to the supply voltage, and resistances add, $R = R_1 + R_2$. In parallel there are separate paths: each branch gets the full supply voltage, and the components work independently, which is why house circuits are wired in parallel.

How this module is examined

• Track the charge. Use $Q = It$ and remember that current is charge per second.
• Rearrange Ohm's law. Use $V = IR$ to find any of the three quantities, keeping units consistent.
• Compare series and parallel. Same current and added voltages in series; same voltage and independent branches in parallel.

Check your knowledge

Recall and calculation questions across the module. Attempt them, then check the worked solutions.

1. State what is meant by electric current. (1 mark)
2. A current of $3.0\ \text{A}$ flows for $20\ \text{s}$. Calculate the charge that flows. (2 marks)
3. State Ohm's law. (2 marks)
4. Two resistors of $2.0\ \Omega$ and $4.0\ \Omega$ are connected in series. Calculate the total resistance. (2 marks)
5. State one reason house lighting is wired in parallel. (1 mark)