The Lens Lab
Bend light to your will. Meet converging and diverging lenses, build a ray diagram, tell real images from virtual ones, and calculate magnification.
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The Lens Lab 🔍
A **lens** is a shaped piece of glass or plastic that bends light by **refraction**. Light refracts once as it enters the lens and again as it leaves — bending the rays to form an **image**. Glasses, cameras, projectors and magnifying glasses all rely on lenses. Time to find out how they work.
Two kinds of lens 🔬
There are two types: • A **converging (convex)** lens is **thicker in the middle**. It bends parallel rays *together*, meeting at the **principal focus**. • A **diverging (concave)** lens is **thinner in the middle**. It bends parallel rays *apart*, so they spread out as if coming from a focus behind the lens.
Match each term to its description
- Converging lens
- Diverging lens
- Real image
- Virtual image
- Convex — bends parallel rays together to a focus
- Concave — bends parallel rays apart
- Rays actually meet; can be shown on a screen
- Rays only appear to meet; cannot be projected
Spot the converging lens
A lens that is thicker in the middle than at its edges will...?
- Bring parallel rays together — it is a converging lens
- Spread parallel rays apart — it is a diverging lens
- Leave parallel rays unchanged
- Reflect the rays back the way they came
The principal focus 🎯
Rays coming in parallel to the **principal axis** (the centre line through the lens) are refracted so that, for a converging lens, they all pass through a single point: the **principal focus (F)**. The distance from the centre of the lens to F is the **focal length**. A fatter lens bends light more, so it has a shorter focal length.
Real vs virtual images 👁️
A **real image** forms where refracted rays **actually cross**. You can catch it on a screen, and it is **inverted** (upside down) — this is how a projector works. A **virtual image** forms where rays only **appear** to come from. You cannot project it, and it is **upright**. A magnifying glass (object close to a converging lens) and every diverging lens make virtual images.
On the screen
A projector throws a sharp image onto a screen. What kind of image must this be?
- A real image — the rays actually meet on the screen
- A virtual image
- Either — both can be projected
- Neither — images never land on screens
Label the ray diagram
An interactive activity.
Magnification 📐
How much bigger (or smaller) is the image than the object? That is the **magnification**: **magnification = image height ÷ object height** Because it divides a length by a length, magnification has **no units** — it is just a number. A magnification of 3 means the image is three times the height of the object; less than 1 means smaller.
Work out the magnification
An interactive activity.
Find the image height
An interactive activity.
Lab summary
A _____ (convex) lens is thicker in the middle and brings parallel rays to the principal focus. A real image forms where rays actually _____ and can be shown on a _____. Magnification = image height ÷ _____ height, and has no units.