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Science project idea

How tall must a mirror be to see your whole body?

To see your whole body in a flat mirror, the mirror need be only half as tall as you, and it does not depend on how far you stand. You test this with a small mirror, a tape and a friend.

Make it yourself7 numbered steps, the materials and the science, all free.Go to the stepsGet a ready-made kitReady-made models, kits and spare parts in the store under Physics.Browse PhysicsAsk on WhatsAppAsk the head office whether a model or kit for this idea is available.Send a message

What it shows

To see your whole body in a flat mirror, the mirror need be only half as tall as you, and it does not depend on how far you stand. You test this with a small mirror, a tape and a friend.

The science

In a flat mirror the image is as far behind the mirror as you are in front, and the angle of incidence equals the angle of reflection. The light from your head and feet reaches your eye after bouncing at points that lie halfway between your eye and head, and halfway between eye and feet. So the mirror needs to span only half of your height.

Materials

Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.

  • A flat mirror about 15 cm wide
  • Masking tape
  • A tape measure and a metre ruler
  • A wall
  • A partner to measure
  • A marker pen
  • A notebook

Safety

For this project: Fix the mirror so it does not fall, and an adult must handle any glass mirror. Do not place a mirror in the sun where it could reflect light into eyes.

Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.

All the safety rules

Step by step

7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.

  1. Tape a mirror on the wall with its bottom edge 80 cm above the floor.

  2. Stand 1 metre from the mirror and look at your reflection.

  3. Ask your partner to put a piece of tape on the mirror where you see the top of your head.

  4. Mark another tape piece where you see your feet, if any, or the lowest part you can see.

  5. Measure the distance between the two tape marks and compare it with half of your height.

  6. Move back to 2 metres and repeat the marks to check that distance does not matter.

  7. Draw a ray diagram with your eye, head and feet showing the reflection points.

What you should see

The visible stretch of mirror is half of your height at both distances, which shows the mirror height needed does not depend on how far you stand.

Viva questions

A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.

1How tall must a mirror be?

Half the height of the person.

2Does distance change this?

No, the half rule holds at any distance.

3What is the law of reflection?

The angle of incidence equals the angle of reflection.

4Where is the image in a plane mirror?

As far behind the mirror as the object is in front.

Free ebook: Viva Questions for Science Projects

Take it further

Find the minimum mirror height for someone shorter or taller than you and check the rule.

Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.

Free ebooks for this project

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