Light and Lenses – Exploring Optics With Simple Setups

Optics doesn’t need complicated equipment. With a few lenses, a light source, and a screen, students can explore the behaviour of light, understand how images form, and see the principles behind cameras, microscopes, and the human eye.

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Setting Up the Experiment

A basic optics bench or even a metre ruler works perfectly. Students use:

• A light box or torch to produce a narrow beam. A candle is a good fun alternative.

• Convex and concave lenses of known focal lengths.

• A screen to capture the image.

By moving the lens and screen, students can find the image position and magnification for different object distances.

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The Science

Convex lenses focus light to a point, forming a real image on the screen when the object is beyond the focal point. Concave lenses diverge light, forming a virtual image that can only be seen by looking through the lens.

The relationship between object distance (u), image distance (v), and focal length (f) is given by the lens equation:

$$\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$$

By measuring u and v, students can calculate f and test the equation for different lenses.

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Typical Results

Lens Type	Object Distance (cm)	Image Distance (cm)	Calculated f (cm)
Convex	20	10.0	6.7
Convex	25	8.3	6.8
Convex	30	7.5	6.7

The results confirm a consistent focal length and help students visualise how lenses bend light.

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Extensions

• Explore magnification by measuring image and object heights.

• Combine two lenses to build a simple telescope or microscope.

• Investigate how lens curvature affects focal length.

• Use PASCO light sensors to measure light intensity and test inverse-square relationships.

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Why It Works in Teaching

Students often find ray diagrams abstract. Simple hands-on setups make light behaviour visible and measurable. By moving the lens and watching the image shift or sharpen, they connect equations to real observations.

Optics becomes more than drawing arrows on paper — it becomes an exploration of how we see the world.