Ray Diagrams that Work
The concave mirror image walk
What this lesson covers
Why it matters
One concave mirror can be a dentist's magnifier, a make-up mirror, a projector and a telescope's heart — depending only on where you stand. Walk the axis and meet all four.
The idea in plain words
The four exam cases. Tap the landmarks.
where it stands decides what it becomes
Where must a face be for a concave make-up mirror to show it magnified and upright?
Closer than f — which is why make-up mirrors have long focal lengths
- case 1: beyond C — image between F and C: real, inverted, smaller
- case 2: at C — image at C: real, inverted, equal — the calibration point
- case 3: between C and F — image beyond C: real, inverted, LARGER — the projector zone
- case 4: inside F — image behind the mirror: virtual, erect, magnified — the shaving/dentist zone
- Upright + magnified = virtual image
- Only one zone gives virtual: INSIDE the focus
Predict first
An object stands exactly AT the centre of curvature C of a concave mirror. Its image is…
C is the self-service point: rays through C strike the mirror head-on and retrace. Object at C → image at C, same size, upside down.
- at C too — real, inverted, SAME size — correct
- at F, diminished
- behind the mirror, magnified
What you do
Slide the candle from far beyond C to inside F — visit all four regions and watch the image flip from cinema-screen to shaving-mirror.
Check yourself
A convex mirror ALWAYS forms an image that is…
The one-trick mirror: it can only shrink and stay upright — which is exactly its job (next lesson).
To throw a candle's image onto a wall, the candle must stand…
Screens need REAL images; concave-outside-F is the only mirror recipe for one.
An object at F of a concave mirror gives an image…
The searchlight case: bulb at focus, parallel beam out — car headlights are built on this sentence.
- virtual, erect and diminished — whatever the object distance — correct
- real and inverted
- magnified
- outside the focus of a CONCAVE mirror — correct
- inside the focus
- anywhere before a convex mirror
- at infinity — reflected rays leave parallel — correct
- at F
- at P