See through it, not in it
A lens is clear and curved; light passes through it.
A drop on the print
Through a flat glass window, everything looks the same size and shape. Now put a drop of water on a glass strip lying on some small print.
How do you think the letters under the drop will look?
What this lesson covers
The idea
A lens is a piece of transparent material, usually glass or plastic, with curved surfaces; unlike a mirror it lets light pass through, so we see things through a lens rather than in it.
A drop on the print
Through a flat glass window, everything looks the same size and shape. Now put a drop of water on a glass strip lying on some small print.
How do you think the letters under the drop will look?
- Larger than the letters nearby
- Exactly the same
- They will disappear
What is on the print?
Put each thing on the small print. Watch the letters. Look at the side view too: does light pass through, or come back?
A lens
A lens is a piece of transparent material, usually glass or plastic, with curved surfaces. Unlike a mirror, it lets light pass through, so we see things through a lens rather than in it.
A magnifying glass helps us read small print by making the letters look bigger.
- Put on the print | What we see
- Flat glass | Letters the same: flat, not a lens
- Water drop | Letters larger: curved, acts like a lens
- Magnifying glass | Letters larger: it is a lens
- Mirror | No letters: light does not pass through
Notes
A lens is a piece of transparent material (usually glass or plastic) with curved surfaces. It lets light pass through: we see things through a lens, not in it.
Check yourself
Which of these is a lens?
How is a lens different from a mirror?
Why do the letters under a water drop look larger?
- A magnifying glass — correct. Yes. It is clear, with curved surfaces, and light passes through it.
- A flat window pane. It is transparent, but its surfaces are flat. A lens has curved surfaces.
- A shiny metal spoon. A spoon reflects light. It acts like a mirror, not a lens.
- A lens sends light back to us. That is what a mirror does.
- Light passes through a lens, so we see things through it — correct. Yes. In a mirror, light comes back and we see images in it.
- A lens is always made of metal. A lens is made of transparent material, usually glass or plastic.
- The drop's surface is curved, so it acts like a lens — correct. Yes. A curved, transparent drop is a simple lens.
- The water makes the ink spread. The ink does not change. The curved drop changes how the letters look.
- The drop acts like a mirror. Light passes through the drop. A mirror would send it back.