3.1.1Unit 6: Light and objects in space
Reflection — Cambridge Checkpoint Physics 0893 Revision Notes & Topical Questions
5 min read 9 parts Lesson 2 of 8 Unit quiz
Lesson summary
3.1.1 Reflection — Notes — CHECKPOINT PHYSICS 0893 notes: State the law of reflection and draw ray diagrams for reflection from a plane mirror.Plane mirror = a flat mirrorCurved surfaces — a spoon gives a distorted reflectionLight rays — light travels in straight lines called ray…
- Drawing rays
- Incident ray
- Reflected ray
- Angle of incidence
- Angle of reflection
- Measuring angles
Section 1 of 9Reflection from mirrors
Plane mirror
Plane mirror a flat mirror
Curved surfaces
- Curved surfaces a spoon gives a distorted reflection
Light rays
- Light rays light travels in straight lines called rays
Drawing rays
- Drawing rays use a ruler and put an arrowhead on each ray to show its direction
Section 2 of 9Terms in a ray diagram
Incident ray
Incident ray the ray arriving at the mirror
Reflected ray
Reflected ray the ray that leaves the mirror
Normal
Normal a dashed line perpendicular (at 90°) to the mirror where the incident ray meets it
Angle of incidence
Angle of incidence the angle between the incident ray and the normal
Angle of reflection
Angle of reflection the angle between the reflected ray and the normal
Measuring angles
- Measuring angles angles are measured from the normal and not from the mirror
Section 3 of 9Law of reflection
Law
Law something that always applies
Statement
- Statement the angle of reflection is equal to the angle of incidence
Same plane
- Same plane the incident ray, the normal and the reflected ray lie in the same flat surface
Section 4 of 9Drawing a reflection ray diagram
1
Draw the mirror and the incident ray, with a ruler, meeting the mirror.
2
Draw the normal at the point where the incident ray meets the mirror, using a protractor or set square.
3
Measure the angle of incidence between the incident ray and the normal.
4
Measure an equal angle on the other side of the normal.
5
Draw the reflected ray along this line with an arrowhead.
6
Label the incident ray, reflected ray, normal and both angles.
Section 5 of 9Uses of reflection
1Rear-view mirrors
- Rear-view mirrors a driver sees a cyclist behind because light from the cyclist reflects from the mirror into the driver's eye
2Motorcycle mirrors
- Motorcycle mirrors the rider sees objects behind
3Seeing hidden objects
- Seeing hidden objects a mirror can be placed so that a reflected ray reaches the eye
Section 6 of 9Investigating the law of reflection
1
Stand a plane mirror vertically on white paper with modelling clay and draw a line along its front.
2
Draw a normal at the mirror surface with a protractor.
3
Direct a ray of light from a ray box onto the mirror at the normal.
4
Mark pencil points along the incident and reflected rays.
5
Remove the mirror, join the points and measure the angle of incidence and the angle of reflection.
6
Repeat for at least four more angles and record in a table.
Section 7 of 9Results of the investigation
Independent variable
- Independent variable the angle of incidence
Dependent variable
- Dependent variable the angle of reflection
Graph
- Graph a straight line of best fit through the origin
Pattern
- Pattern the angle of reflection equals the angle of incidence
Accuracy
- Accuracy marking rays precisely is difficult, so a thin ray and repeated measurements help
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Reflection | Light bouncing off a surface. |
| Incident ray | Ray of light arriving at a surface. |
| Normal | Line at 90° to a surface. |
| Angle of incidence | Angle between incident ray and normal. |
| Angle of reflection | Angle between reflected ray and normal. |
| Plane mirror | Flat mirror. |
| Law of reflection | Angle of reflection equals angle of incidence. |
Section 9 of 9Exam technique
1
Measuring angles from the mirror surface — angles are measured from the normal.
2
Thinking the angle of reflection can differ from the angle of incidence — they are equal for a plane mirror.
3
Drawing the normal as a solid line that looks like a ray — it is dashed.
4
Forgetting arrowheads on rays — they show the direction of travel.
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