Circuit Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Circuit.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

A closed loop of conducting material through which electric current can flow, typically including a power source and one or more components.

A circuit is a complete loop — like a circular track that electrons run around. Break the loop and everything stops.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Current only flows when the circuit is complete — a break anywhere stops the entire flow.

Common stuck point: A switch works by physically breaking the circuit (open = off, closed = on).

Sense of Study hint: When analysing a circuit, first trace the path from the positive terminal of the power source through each component and back to the negative terminal. Check whether the loop is complete — if there is any break, no current flows. Then identify whether components are in series (one path) or parallel (branching paths).

Worked Examples

Example 1

easy
A simple circuit has a 9 \text{ V} battery and a 3 \text{ } \Omega resistor. What is the current in the circuit? What happens if the circuit wire is cut?

Solution

  1. 1
    Apply Ohm's law: I = \frac{V}{R} = \frac{9}{3} = 3 \text{ A}.
  2. 2
    The current flows from the positive terminal through the resistor and back to the negative terminal.
  3. 3
    If the wire is cut, the circuit is open (broken) and no current flows. A complete loop is required for current to flow.

Answer

I = 3 \text{ A}
A circuit is a complete conducting loop through which electric current can flow. Breaking the loop at any point stops all current flow. The battery provides the energy (EMF) to drive current around the circuit.

Example 2

medium
A circuit has a 12 \text{ V} battery, a 4 \text{ } \Omega resistor and a 6 \text{ } \Omega resistor in series, with a switch. When the switch is closed, what is the current and the voltage across each resistor?

Example 3

medium
A circuit has a 9 \text{ V} battery and a 15 \text{ } \Omega resistor. Find the current flowing and the power consumed.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
A circuit has a battery and three identical bulbs. Two bulbs are in parallel with each other, and this parallel pair is in series with the third bulb. If the battery is 6 \text{ V} and each bulb has resistance 6 \text{ } \Omega, what is the current from the battery?

Example 2

hard
A circuit has a 24 \text{ V} battery with internal resistance r = 1 \text{ } \Omega connected to an external resistance R = 11 \text{ } \Omega. What is the current, the terminal voltage of the battery, and the power dissipated internally?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

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