The laws of reflection

A concave mirror converges light and can form images that are enlarged, same size or diminished, and erect or inverted, depending on the object’s distance. A convex mirror diverges light and always gives an erect, diminished image.

In real life: A concave mirror in a torch gathers light into a beam, while a convex mirror gives a driver a wide view behind.

Worked example 1

Question. Light hits a mirror at 30° to the normal. At what angle does it reflect?

Answer: It reflects at 30° to the normal.

Lenses

When an object is beyond the focus of a convex lens, the rays meet on the far side to form a real, inverted image, as the ray diagram shows. This is how a camera and the eye form their images.

In real life: A magnifying glass is a convex lens; held close, it makes a larger, upright image of small print.

Worked example 2

Question. An object is placed far in front of a convex lens. What kind of image forms?

Answer: A real, inverted image forms on the other side of the lens.

Worked example 3

Question. What kind of image does a convex mirror always form?

Answer: A convex mirror always forms an erect, diminished image, giving a wide view.