Q & A is the best way for parents to help a student to review the topic. It is interactive, fun and you will most likely learn something in the process too. As for the student, often than not, (s)he will pickup something that (s)he didn't understand clear enough to say it in his own words.
- The most common questions on "Geometrical Optics" is about the image formed from a mirror and lens, it can be a question on
- real image vs virtual image
- the image is upright/erect or inverted?
- the image is smaller or bigger than the original image?
You can of course use mirror equation and lens equation as shown below. However it is sometime confusing as whether a positive or negative value should be used. So I strongly recommend you to use a simple drawing to verify your answer from using the equation.
Some facts to remember
- Which side is the real image?
For mirrors, the real side is the same side as the object. For lenses, the real side is the opposite the object. Think of a projector.
- Convex/Diverging lens can only form a virtual image and it is always smaller than the real image. If your eyes are shortsighted, try your glasses
- For convex/converging lens
Virtual image is always larger, however real image can be larger or smaller.
| Object to the center | Image |
| Between f and 2f | real, magnified, inverted, think of a projector lens |
| Greater than 2f | real, smaller, inverted |
| Less than f | Virtual, magnified, upright, think of a magnifying glass or reading glass |
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