Converging and Diverging Lenses

Lab Brief #3

🎯 Your mission

Predict it first. Then prove yourself right (or wrong).

⚡ The twist

The opposite of what you expect is often what happens.

What you'll learn

A convex lens brings parallel rays to a focus and can form a real, invertible image; a concave lens spreads them and always forms a virtual, upright, smaller one. Focal length sets the power: the shorter the focal length, the stronger the lens.

Key words

focal length
The distance from a lens to the point where parallel rays converge.
real image
An image formed where light rays actually meet, so it can be projected onto a screen.

Make a hypothesis first

Predict: what happens if you double the force?

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

convex lens
concave lens
lamp
screen or card
metre rule
lens holder

Get ready

⚠️ Safety first

Never use a lens to focus sunlight — it starts fires and can blind.
The lamp gets hot; let it cool before moving it.

Step 1 of 4 · Read

Think about what you just learned: say what "focal length" and "real image" mean in your own words before you start.

Step 2 of 4 · Do

Use a convex lens to project a window onto a card and measure the focal length. Then move a lamp from beyond 2f to inside f, recording at each stage whether the image is real or virtual, upright or inverted, larger or smaller.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

A concave lens always forms an image that is:

How sure are you?😐 maybe

Question 2 of 2

A shorter focal length means the lens is:

How sure are you?😐 maybe

Mind = blown

🔥 A bolt of lightning is 5 times hotter than the surface of the sun.

Nice work!

You got 0 of 2 right.

Next: Dispersion and Colour All lessons

🎯

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✨ More to explore

🌍 Where you see this in real life: You use this every time you flip a light switch, ride a bike, or kick a ball.

🏆 Stretch challenge (try it this week): Time how long a small ball rolls down something, then change the slope and try again.

👨‍👩‍👧 For the dinner table: “Show me something at home that uses this kind of energy.”

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Converging and Diverging Lenses

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