Light and optics is a chain: refraction explains how light bends, bending explains lenses, and lenses explain instruments. A weak link near the start spreads to the rest.
This section is part of SPM Physics. The lens and image formation explorer lets you test your own predictions.
How do the parts connect?
Study the lessons in this order.
- Refraction and refractive index describe how light bends at a boundary.
- Total internal reflection is the limiting case, when light cannot leave the denser material.
- Ray diagrams for lenses use refraction to locate images.
- Image position and magnification put numbers on the diagram.
- Optical instruments combine lenses for a purpose.
Each step reuses the one before it.
One short example
A converging lens has a focal length of 10 cm. An object stands 30 cm from it. Using 1 ÷ f = 1 ÷ u + 1 ÷ v, 1 ÷ v = 1 ÷ 10 − 1 ÷ 30 = 2 ÷ 30, so v = 15 cm.
The magnification is v ÷ u = 15 ÷ 30 = 0.5. The image is real, inverted and half the size of the object. A ray diagram drawn to scale should show the same thing, which is why diagram and calculation check each other.
Who should start where?
Pick the row that matches the difficulty you notice most.
| Your difficulty | Start with |
|---|---|
| Bending of light, refractive index | applying refraction and refractive index |
| Light staying inside glass or water | explaining total internal reflection |
| Drawing lens rays | drawing ray diagrams for lenses |
| Image distance and size | calculating image position and magnification |
| Telescopes and microscopes | explaining optical instrument principles |
When each feels steady, use the light and optics practice set.
To have a teacher connect the diagrams and calculations with you, see online one-to-one Physics tuition.