Year 6 Science: Reflection with a mirror
Part of the Year 6 Science how we see chapter. Chapter overview · whole chapter on one page
Reflection with a mirror
A mirror is a smooth, shiny surface that reflects most of the light that hits it. The light that arrives at the mirror is the incoming ray. The light that bounces off is the reflected ray.
The line at right angles to the mirror is called the normal. The incoming ray and the reflected ray make equal angles with the normal.
Ruby tested three rays on a mirror and recorded the angles measured from the normal.
| Ray | Angle of the incoming ray (degrees) | Angle of the reflected ray (degrees) |
|---|---|---|
| Ray a | 30 | 30 |
| Ray b | 45 | 45 |
| Ray c | 60 | 60 |
Key ideas
- A mirror reflects light.
- The incoming ray and the reflected ray make equal angles with the normal.
- The normal is a line at right angles to the mirror.
- A mirror reflects light that hits it, so it can send light into your eyes.
Method. Read the row for Ray a.
- Read the row. The incoming angle for Ray a is 30 degrees.30
- Use the rule. The reflected angle is equal to the incoming angle.30 degrees
- Write the answer. 30 degrees
Check. The two angles are equal, so the rule holds. ✓
Method. Use the rule for reflection.
- Read the rule. The reflected angle equals the incoming angle.equal
- Apply the rule. The reflected angle is 45 degrees.45 degrees
- Write the answer. 45 degrees
Check. Ray b was measured as 45 degrees on both sides. ✓
Method. Add all six angles.
- Add the incoming angles. The incoming angles are 30, 45 and 60.30 + 45 + 60 = 135
- Add the reflected angles. The reflected angles are also 30, 45 and 60, so the total is 135 + 135.135 + 135 = 270
- Write the answer. 270 degrees
Check. Each pair is equal, so the total is twice 135. ✓
Watch out
Watch out: the angles are measured from the normal, not from the mirror. A ray that hits the mirror at 30 degrees to the surface is 60 degrees from the normal.
Exam tip
Exam tip. Measure the angles from the normal line, and say that the reflected angle is equal to the incoming angle.
Try it (with your teacher, or a grown-up at home). In a dim room, with a grown-up, shine a torch at a small mirror laid flat on a table. Do not shine the torch or the reflection into anyone's eyes. Hold a card at the angle the light bounces. Measure the angle on each side of a line drawn at right angles to the mirror.
Exercise 8B Reflection with a mirror
Method. Read the definition.
- Read the definition. The line at right angles to a mirror is the normal.normal
- Write the answer. normal
Check. Angles are measured from the normal. ✓
Method. Read the definition.
- Read the definition. The light that arrives at the mirror is the incoming ray.incoming ray
- Write the answer. incoming ray
Check. The light that bounces off is the reflected ray. ✓
Method. Read the definition.
- Read the definition. The light that bounces off the mirror is the reflected ray.reflected ray
- Write the answer. reflected ray
Check. The incoming and reflected rays are both measured from the normal. ✓
Method. Read the row for Ray c.
- Read the row. The incoming angle for Ray c is 60 degrees, and the reflected angle is also 60 degrees.60
- Write the answer. So the reflected angle is 60 degrees.60 degrees
- Write the answer. 60 degrees
Check. The two angles are equal. ✓
Method. Check each row.
- Check the rows. In each row, the incoming and reflected angles are the same.same
- Decide. So the answer is yes.yes
- Write the answer. yes
Check. The rule holds for all three rays. ✓
Method. Read the description.
- Read the description. A smooth, shiny surface that reflects light is a mirror.mirror
- Write the answer. mirror
Check. A mirror is a reflector. ✓
Method. Use the rule.
- Use the rule. The reflected angle equals the incoming angle.equal
- Write the answer. So the reflected angle is 45 degrees.45 degrees
- Write the answer. 45 degrees
Check. Ray b is 45 degrees on both sides. ✓
Method. Add the two angles.
- Read the row. The incoming angle is 30 and the reflected angle is 30.30 and 30
- Add. The total is 30 plus 30.30 + 30 = 60
- Write the answer. 60 degrees
Check. Both angles are equal to 30 degrees. ✓
Method. Use the rule.
- Use the rule. The reflected angle equals the incoming angle.equal
- Write the answer. So the reflected angle is 25 degrees.25 degrees
- Write the answer. 25 degrees
Check. The rule holds for any incoming angle. ✓
Method. Check the table.
- Check the table. In every row the reflected angle equals the incoming angle, so none is bigger.equal
- Decide. So Priya is not right.no
- Write the answer. no
Check. The angles are equal, not bigger. ✓
Method. Think about reflection.
- Think about the mirror. The mirror reflects the light that hits it.reflects
- Think about the eyes. The reflected light then travels into your eyes.eyes
- Write the answer. Accept any sentence that says the mirror reflects the light that hits it, so the reflected light can reach your eyes.
Check. Reflected light can be seen. ✓
Method. Think about measuring angles.
- Think about the fixed line. The normal gives a fixed line to measure from.fixed line
- Think about comparison. So the incoming and reflected angles can be compared fairly.compared
- Write the answer. Accept any sentence that says the normal gives a fixed line to measure both angles from, so they can be compared.
Check. A fair measurement uses the same reference line. ✓
Method. Think about the normal.
- Think about the mirror. A mirror at a steeper angle has a different normal.different normal
- Think about the reflection. So the reflected ray leaves in a different direction.different direction
- Write the answer. Accept any sentence that says the normal changes with the mirror, so the reflected ray leaves at a different direction.
Check. The reflected direction depends on the normal. ✓