Below you will find some commonly asked questions about light and lenses. You may also want to explore other activities related to light under Lesson Plan Ideas or Student Activities for the school program.
The angle of incidence (incoming ray) equals the angle of reflection (reflected ray).
Try this out in a dark room with a flashlight and a mirror.
You have probably heard of fibre optics. These are fine transparent rods of plastic or glass that can carry telephone messages and other information. In fibre optic applications, the message is transformed into a light ray, which is then shot through one end of a transparent rod of plastic or glass, coming out the other end. This can be done even if the rod is bent into a curve. The transparent rod is made of two layers; the light travels in the inner layer and is reflected internally by the second, outer layer. Very little light is lost through the sides of the rod because there is a high degree of total internal reflection. Nearly 100% of the beam is reflected. That is how the light travels down the tube. At the end of the tube, the light is transformed again back into the original voice message or information.
Reflecting telescopes have become very important in the exploration of space. Telescopes use both mirrors and lenses to produce close-up images of distant objects such as stars and planets. In reflecting telescopes, the first or primary mirror is concave and is the largest mirror. The larger it can be, the better, because as the size goes up, the amount of light collected goes up.
A telescope is really a big "light bucket". The primary mirror reflects the incoming light to a focal point. From this "prime focus", another mirror (flat or curved) reflects the light to a focus at a more convenient point for you to place your eye or attach a piece of instrumentation, such as a camera - usually at the back or side of the telescope tube.
In refracting telescopes, large lenses bend or refract the light to a focus, but these telescopes are much more difficult and expensive to build and can only be about 1 meter in diameter. By contrast, the largest reflecting telescopes are now 10 meters in diameter.
Light is a form of radiant energy. We only see a very small portion of what is called the electromagnetic spectrum. If you hold a magnifying glass in the sunlight and focus it on a piece of paper, you can burn a hole in the paper. This heat energy does not come from the magnifying glass. It comes from the Sun, and includes not only visible light but also ultra violet and infra-red energy.
Which of the following are sources of light?
Periscopes use mirrors (or 45 degree glass prisms) to direct light around corners. In a simple periscope, 2 flat mirrors each reflect the light (usually through 90 degrees) enabling an observer to see over walls, around corners and over people's heads in a crowd. Periscopes are particularly important in submarines because they enable the crew to view objects on and above the surface of the water.
When white light shines on a red apple, the apple skin absorbs all of the colours in white light except red. The red light is reflected into our eyes and we see the apple as red. We see a white object as white because it reflects all the colours into our eyes. An object that appears black has absorbed all the colours of the white light and reflects nothing back to our eyes.
