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Ohm's Law Questions: Free Printable Worksheet for Year 9

  • ForYear 9
  • StageKey Stage 3
  • CostFree
  • FormatPrintable PDF
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Ohm's Law Questions is a free printable science worksheet for Year 9 (ages 13 to 14), in Key Stage 3. Children use V = I × R to find voltage, current or resistance. It needs only a pencil, and page 2 gives the grown up notes, help ideas, a stretch task and the answers.

It comes from the Mini Minds Hub, the free library of printables from Jaques of London, the British games and toy company that has been making games for families since 1795. Print both pages, give page 1 to your child and keep page 2 for yourself. Black and white printing works well.

What is on the sheet

Children use V = I × R to find voltage, current or resistance. Each question gives two values with their units and asks for the third. Some questions ask for voltage, some for current and some for resistance, so children must rearrange the equation rather than repeat one pattern. One question uses a decimal. There is space to write each answer. Children should write the equation, put the numbers in and give the unit.

  • I = 2 amps, R = 5 ohms. Find V.
  • I = 3 amps, R = 4 ohms. Find V.
  • V = 12 volts, R = 6 ohms. Find I.
  • V = 20 volts, R = 4 ohms. Find I.
  • V = 9 volts, I = 3 amps. Find R.
  • V = 24 volts, I = 6 amps. Find R.
  • I = 0.5 amps, R = 10 ohms. Find V.

Worked example

I = 7 amps, R = 8 ohms. Find V.

This is a different question from the ones on the sheet. It shows two ways to set out the working.

Method 1: equation first
  1. Write the equation: V = I × R.
  2. Put the numbers in: V = 7 × 8.
  3. Multiply: V = 56.
  4. Add the unit. Voltage is measured in volts.
Method 2: formula triangle
  1. Draw a triangle. Put V in the top part, and I and R side by side in the bottom part.
  2. Cover the letter you want to find. Covering V leaves I next to R, so multiply them.
  3. Work out 7 × 8 = 56 and write the unit.
V = 56 volts

Building confidence with equations

Say it in words

Before using any numbers, ask your child to say what the equation means. Voltage equals current times resistance. Saying it aloud helps the letters stop feeling like code.

Write every step

Ask for three lines each time: the equation, the numbers put in, then the answer with its unit. Neat working makes mistakes easy to spot and fix.

Rearrange before calculating

When the missing value is current or resistance, write the rearranged equation on its own line first. Do this before any numbers go in.

Check by going backwards

Put the answer back into V = I × R. If the numbers agree with the question, the answer is very likely right.

What is Ohm's law?

Ohm's law links three ideas in an electric circuit: voltage, current and resistance. Voltage is the push from a cell or battery. Current is the flow of charge round the circuit. Resistance is how much a component holds that flow back. For many everyday components the three are linked by V = I × R.

The equation can be rearranged to find any one of the three if the other two are known. That is why the skill matters in Key Stage 3 science. Children are not just remembering a formula. They are choosing the right form of it, substituting values and giving a unit. These habits carry into later physics and into maths.

This sheet is paper based and needs no equipment. If you talk about real circuits, only use small batteries. Never let children experiment with mains sockets, plugs or appliances. Mains electricity is dangerous.

Quick facts about electricity

  • The unit of resistance, the ohm, is named after the German physicist Georg Ohm.
  • The volt is named after the Italian scientist Alessandro Volta, who worked on early batteries.
  • The amp, the unit of current, is named after the French scientist André Marie Ampère.
  • The symbol for the ohm is the Greek capital letter omega, Ω.
  • A typical AA battery is marked 1.5 volts, while mains electricity in UK homes is about 230 volts.

Skills and curriculum link

  • Using equations
  • Rearranging
  • Substituting values
  • Units
  • Checking answers
  • Scientific reasoning

This sheet supports the area below. It is matched to the published England framework. Please check it against your own school plan.

Framework Subject or area Strand Year
National Curriculum (England) Science Physics: current electricity Year 9

What children will be able to do

  • I can use V = I × R.
  • I can find voltage, current or resistance by rearranging the equation.
  • I can give my answer with the right unit.

Helpful ideas for working through the sheet

  • Equation firstAlways write V = I × R before using any numbers. It gives children a clear starting point and shows their thinking.
  • Formula trianglePut V on top, with I and R below. Cover the letter you want to find and the triangle shows what to do with the other two.
  • Units matterVoltage uses volts, current uses amps and resistance uses ohms. An answer without a unit is only half an answer.
  • Sense checkAsk whether the answer is a sensible size. Then put it back into the equation to see if everything agrees.

Key words

  • VoltageThe push that drives current round a circuit. It is measured in volts.
  • CurrentThe flow of electric charge round a circuit. It is measured in amps.
  • ResistanceHow much a part of a circuit holds back the current. It is measured in ohms.
  • OhmThe unit of resistance. Its symbol is Ω.
  • RearrangeChange an equation so that a different quantity is on its own.
  • SubstituteReplace a letter in an equation with its value.

How to use it

  1. Print both pages. Page 1 is for your child. Keep page 2, which has the notes and answers.
  2. Read the first question together. Ask which quantity is missing and which two are given.
  3. Write the equation first, then put the numbers in. A formula triangle can help with rearranging.
  4. Check against page 2. Ask, "How did you decide what to do?" The method matters as much as the answer.
  5. Come back another day and redo any questions that felt tricky. Repeating a familiar sheet builds confidence.

Help, stretch and game ideas

If it feels too hard

Do one question together and write each step on its own line. Start with a question where voltage is missing, because it only needs multiplying. Draw a formula triangle and cover the letter you want. Then try one where current is missing.

To stretch confident children

Make up two more questions with different numbers, one finding current and one finding resistance. Write the answers on a separate piece of paper. Swap with a friend or family member, solve each other's questions and check the working.

Make it a game

Look at a battery and talk about the voltage printed on it. Then invent a question using that voltage and a resistance of your choice. Only use small batteries, never mains sockets. Take turns to write questions and solve them.

Mistakes to watch for

Watch forA child multiplies the two given numbers every time, even when voltage is already given.

Try thisAsk which quantity is missing. Write the rearranged equation on its own line before putting any numbers in.

Watch forThe answer has no unit, or the wrong one.

Try thisMatch each quantity to its unit before starting: volts, amps and ohms. Ask them to circle the unit in the question.

Watch forA decimal in the question causes a slip in the arithmetic.

Try thisEstimate first. Ask whether the answer should be bigger or smaller than the other numbers, then check with the working.

Talk about it

  • How do you know which quantity is missing in a question?
  • Why do we write the equation before the numbers?
  • How does the formula triangle help you rearrange?
  • What units go with voltage, current and resistance?
  • Can you check an answer by putting it back into the equation?
  • Where might you see voltage written on an object at home?

Take it off the page

Battery hunt

Find small batteries around the home and read the voltage printed on each one. Make a list. Do not open or damage batteries, and keep them away from mains sockets.

Triangle cards

Draw a formula triangle on card. Cover each letter in turn and say aloud the equation it shows. Repeat until it feels easy.

Question writers

Choose two values and write a full question with units. Put the answer on the back of the page, then ask someone else to solve it.

Who it is for

Parents

Sit with your child for the first question, then let them lead. Ask them to explain each step. You do not need to know the physics. Use the answers on page 2 to check together.

Teachers

Use it as a starter, plenary, early finisher task, homework or cover lesson. It needs no preparation beyond printing. Page 2 gives help and stretch ideas, so it works across a mixed ability class.

Home educators

Print it as part of a wider science plan. It pairs well with a look at real batteries and circuit diagrams. Reprint it for brothers and sisters, or for revision a few weeks later.

Where this fits in science

Before this sheet, children meet simple circuits, circuit symbols and the ideas of current and voltage. They learn that current flows round a complete loop. They also need confidence with multiplying, dividing and substituting into equations.

After this, children can meet series and parallel circuits in more detail, and later GCSE physics uses the same equation with more complex circuits and graphs. Rearranging and giving units carefully now makes that later work much smoother.

Check it worked

Ask these when the sheet is finished. Listen for the reasoning, not just the answer.

  1. How do you find current if you know voltage and resistance?
  2. What happens to the current if the resistance goes up?
  3. Which units go with voltage, current and resistance?

Questions parents and teachers ask

What age is Ohm's Law Questions for?

It is written for Year 9 (ages 13 to 14), in Key Stage 3. It suits children who are learning to substitute into and rearrange equations in science, and who have met current and voltage before.

What will children practise?

They use the Ohm's law equation, V = I × R, to find voltage, current or resistance. They also practise rearranging the equation, putting numbers in and giving the correct unit with each answer.

How do I use it?

Print both pages and give page 1 to your child. Ask them to write the equation first, then put the numbers in. A formula triangle can help with rearranging. Check with page 2 afterwards.

What if it feels too hard?

Do one question together and write each step on its own line. Start with a question where voltage is missing, then move on to the others. Page 2 has more help ideas for the grown up.

Is it free?

Yes. It is free to print for home and classroom use. You can print it again for brothers, sisters or revision whenever you like.

Can teachers use it in class?

Yes. It works as a starter, plenary, early finisher task, homework or table activity. It needs no preparation beyond printing, and page 2 gives support, a stretch idea and answers.

Do I need to print in colour?

No. It prints well in black and white on plain A4 paper. Colour is not needed to complete any part of the sheet, so a standard home or school printer is fine.

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Made by Jaques of London, making games for families since 1795. A printable supports classroom learning and does not replace a teacher.

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