Last reviewed: 10 November 2026
Updated November 2026. These Grade 9 curved mirrors notes explain concave and convex mirrors, the terms used to describe them, how to locate images with ray diagrams, the characteristics of images for different object positions, and everyday uses. A concave mirror curves inwards like a cave and can form real or virtual images; a convex mirror bulges outwards and always forms a virtual, upright, diminished image, which is why it is used as a vehicle side mirror and in shops.
The questions are original practice for Kenyan junior school learners, not an official paper. For other Grade 9 science topics, see the Grade 9 Integrated Science revision guide and the Grade 9 notes hub. You may also find our Grade 9 notes on waves useful for the other Force and Energy sub-strand.
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What the Grade 9 Curriculum Covers
Curved mirrors is a sub-strand under Force and Energy in the Kenya Institute of Curriculum Development’s Grade 9 Integrated Science design. It covers types of curved mirrors, terms (aperture, pole, centre of curvature, principal axis, radius of curvature, principal focus, focal length, focal plane), ray diagrams, image characteristics for object positions from infinity to between F and P, and uses. The design is listed on the KICD Grade Nine curriculum designs page.
Types of Curved Mirrors
- Concave (converging): reflecting surface curves inwards. Parallel rays reflect and meet at the principal focus.
- Convex (diverging): reflecting surface bulges outwards. Parallel rays reflect and spread out as if from a focus behind the mirror.
- Parabolic: a concave mirror shaped as a parabola, which brings parallel rays to a sharp focus; used in solar concentrators and headlamp reflectors.
Key Terms
| Term | Meaning |
|---|---|
| Pole (P) | The centre of the mirror’s surface |
| Centre of curvature (C) | The centre of the sphere the mirror is part of |
| Radius of curvature (r) | Distance from P to C |
| Principal axis | Line through C and P |
| Principal focus (F) | Point where rays parallel to the axis meet (concave) or appear to come from (convex) |
| Focal length (f) | Distance from P to F; for small mirrors f ≈ r ÷ 2 |
| Aperture | The width of the mirror’s reflecting surface |
| Focal plane | Plane through F at right angles to the principal axis |
Drawing Ray Diagrams
Use any two of these standard rays from the top of the object; where the reflected rays meet (or appear to meet) is the top of the image. The same rules are used in OpenStax College Physics’ section on image formation by mirrors.
- A ray parallel to the principal axis reflects through F (concave) or as if from F (convex).
- A ray through F (or heading towards F for convex) reflects parallel to the axis.
- A ray through C (or heading towards C for convex) reflects back along itself.
Draw real rays as solid lines and virtual rays (behind the mirror) as dashed lines.
Images Formed by a Concave Mirror
| Object position | Image position | Nature of image |
|---|---|---|
| At infinity (very far) | At F | Real, inverted, very small |
| Beyond C | Between C and F | Real, inverted, diminished |
| At C | At C | Real, inverted, same size |
| Between C and F | Beyond C | Real, inverted, magnified |
| At F | At infinity | No clear image (reflected rays are parallel) |
| Between F and P | Behind the mirror | Virtual, upright, magnified |
Images Formed by a Convex Mirror
Wherever the object is, the image is behind the mirror, between P and F: virtual, upright and diminished. A convex mirror therefore gives a wide field of view.
Uses of Curved Mirrors
- Concave: shaving and make-up mirrors (object between F and P gives an upright, magnified image); dentists’ mirrors; car headlamp and torch reflectors (bulb at F sends out a parallel beam); solar cookers and concentrators (sunlight focused at F); reflecting telescopes.
- Convex: vehicle side and rear-view mirrors, and security mirrors in supermarkets and at sharp road bends, because they show a wide area.
Original Practice Questions With Worked Answers
- A concave mirror has radius of curvature 30 cm. Estimate its focal length. f ≈ 30 ÷ 2 = 15 cm.
- Where should a bulb be placed in a torch reflector? At the principal focus, so the beam is parallel.
- Describe the image of an object placed at C of a concave mirror. Real, inverted, same size, at C.
- Why are convex mirrors used as driving mirrors? They always give an upright image and a wide field of view.
- Where must your face be for a concave shaving mirror to work? Between F and P.
Cover the answers and attempt each question first. For timed practice, use the Grade 9 revision papers or the Grade 9 CBC Challenge. These notes are free; full revision access is available with the KSh 20 Day Pass or the KSh 500 Monthly Pass.
Frequently Asked Questions
What is the difference between a concave and a convex mirror?
A concave mirror curves inwards and converges light; a convex mirror bulges outwards and spreads light out.
What type of image does a convex mirror form?
Always virtual, upright and smaller than the object.
When does a concave mirror form a virtual image?
When the object is between the principal focus and the pole.
What is the focal length of a curved mirror?
The distance from the pole to the principal focus, about half the radius of curvature.