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

An electrical circuit is a closed path through which electric current flows from a power source, through components, and back to the source.

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: Circuit asks students to follow the circuit path and identify what quantity changes at each component.

Common stuck point: Students often know a formula related to circuit but skip the recognition step: Can I identify the circuit path, what quantity is flowing or changing, and which electrical rule links the quantities? That leads to a correct-looking substitution attached to the wrong physical model.

Sense of Study hint: Ask: Can I identify the circuit path, what quantity is flowing or changing, and which electrical rule links the quantities?

Worked Examples

Example 1

easy
A simple circuit has a 9 V9 \text{ V} battery and a 3 Ω3 \text{ } \Omega resistor. What is the current in the circuit? What happens if the circuit wire is cut?

Answer

I=3 AI = 3 \text{ A}

First step

1
Apply Ohm's law: I=VR=93=3 AI = \frac{V}{R} = \frac{9}{3} = 3 \text{ A}.

Full solution

  1. 2
    The current flows from the positive terminal through the resistor and back to the negative terminal.
  2. 3
    If the wire is cut, the circuit is open (broken) and no current flows. A complete loop is required for current to flow.
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 V12 \text{ V} battery, a 4 Ω4 \text{ } \Omega resistor and a 6 Ω6 \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 V9 \text{ V} battery and a 15 Ω15 \text{ } \Omega resistor. Find the current flowing and the power consumed.

Example 4

medium
A 99 V battery is connected to a 3 Ω3\ \Omega and a 6 Ω6\ \Omega resistor in series. Find the voltage across each.

Example 5

medium
Three 6 Ω6\ \Omega resistors are all in parallel across a 1212 V battery. Find the current from the battery.

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 V6 \text{ V} and each bulb has resistance 6 Ω6 \text{ } \Omega, what is the current from the battery?

Example 2

hard
A circuit has a 24 V24 \text{ V} battery with internal resistance r=1 Ωr = 1 \text{ } \Omega connected to an external resistance R=11 ΩR = 11 \text{ } \Omega. What is the current, the terminal voltage of the battery, and the power dissipated internally?

Example 3

easy
What must be true for current to flow in a circuit?

Example 4

easy
A switch is open in a single-loop circuit. Does current flow?

Example 5

easy
What is a short circuit?

Example 6

easy
Does current get 'used up' as it goes around a single-loop circuit?

Example 7

easy
Name the three basic parts every simple circuit needs.

Example 8

easy
A wire comes loose in a working circuit. What type of circuit results?

Example 9

easy
In a closed loop with a battery and bulb, where does the energy come from?

Example 10

easy
Two bulbs are wired so that all current passes through both in turn. Is this series or parallel?

Example 11

medium
A circuit has a 1212 V battery and a single 6 Ω6\,\Omega load. Is the circuit closed, and what current flows?

Example 12

medium
In a single loop, a switch is added in series with the load. With the switch open, what is the current and the voltage across the open switch?

Example 13

medium
A battery and three identical bulbs are in a single series loop. One bulb burns out (open). What happens to the others?

Example 14

medium
A circuit accidentally shorts across a 1212 V battery with wire of 0.1 Ω0.1\,\Omega. Estimate the current.

Example 15

medium
In a closed circuit, a 99 V source delivers 0.30.3 A. How much power does the circuit consume?

Example 16

medium
Two paths connect the same two nodes, each carrying current independently. Is this series or parallel, and what is shared?

Example 17

medium
A circuit has a battery, a closed switch, and a bulb, but the bulb does not light. The wires are fine. What single fault best explains this?

Example 18

challenge
A 1212 V battery connects to a 4 Ω4\,\Omega resistor in series with a parallel pair (12 Ω12\,\Omega and 6 Ω6\,\Omega). Find the total current and the voltage across the parallel section.

Example 19

challenge
In a single loop, a 1010 V battery, a 2 Ω2\,\Omega resistor, and a bulb of unknown resistance carry 22 A. Find the bulb's resistance and its voltage drop.

Example 20

challenge
A circuit draws 1.51.5 A from a 66 V battery for 44 minutes. How much energy does it deliver, in joules?

Example 21

medium
A closed circuit has a 66 V battery and a 2 Ω2\,\Omega load. What current flows?

Example 22

medium
In a single loop, a switch in series is closed. With a 1010 V source and 5 Ω5\,\Omega load, what current flows?

Example 23

easy
A simple circuit has a 66 V battery and a 2 Ω2\ \Omega resistor. Find the current.

Example 24

easy
A lamp draws 0.50.5 A from a 1212 V source. Find its resistance.

Example 25

easy
A 1010 V battery is connected to a 5 Ω5\ \Omega resistor. Find the power dissipated.

Example 26

easy
What is the role of a switch in a circuit?

Example 27

medium
Two 3 Ω3\ \Omega resistors are in series across a 1212 V battery. Find the current.

Example 28

medium
Two 6 Ω6\ \Omega resistors are in parallel across a 1212 V battery. Find the total current from the battery.

Example 29

medium
A circuit has V=15V = 15 V and I=3I = 3 A. Find the resistance.

Example 30

medium
Two identical bulbs in parallel each have resistance 4 Ω4\ \Omega. What is the combined resistance?

Example 31

medium
A 1212 V battery powers a circuit drawing 0.250.25 A. How much energy does it deliver in 1010 s?

Example 32

medium
In a series circuit, Vtotal=24V_{total} = 24 V across two resistors R1=4 ΩR_1 = 4\ \Omega and R2=8 ΩR_2 = 8\ \Omega. Find the current.

Example 33

hard
A 1212 V source drives current through a 6 Ω6\ \Omega resistor in series with a parallel pair of 4 Ω4\ \Omega and 4 Ω4\ \Omega. Find the total current.

Example 34

hard
In a parallel circuit with two branches (R1=6 ΩR_1 = 6\ \Omega at 1212 V, R2=4 ΩR_2 = 4\ \Omega at 1212 V), find the current in each branch.

Example 35

hard
A 99 V battery with internal resistance 0.5 Ω0.5\ \Omega drives a 4 Ω4\ \Omega external resistor. Find the current.

Example 36

hard
A 6060 W bulb is connected to 120120 V. How much current does it draw?

Example 37

challenge
A circuit has a 2424 V battery, a 2 Ω2\ \Omega resistor in series with a parallel pair of 6 Ω6\ \Omega and 3 Ω3\ \Omega. Find the current in the 6 Ω6\ \Omega resistor.

Example 38

challenge
A 1.51.5 V battery powers a 0.5 Ω0.5\ \Omega flashlight bulb for 3030 minutes. How much energy did the battery deliver?
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Background Knowledge

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

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