Chapter 10 — Light: Mirrors and Lenses

Chapter 10, 'Light: Mirrors and Lenses', is about spherical mirrors (concave and convex), the laws of reflection, and lenses (convex and concave). It explains how images are formed, how these differ from plane mirrors, and where curved mirrors and lenses are used in everyday life.

A concave mirror has a reflecting surface that curves inward, while a convex mirror has a reflecting surface that curves outward. A concave mirror can form erect-enlarged or inverted images depending on the object's distance, whereas a convex mirror always forms an erect and diminished image.

The two laws of reflection are: (1) the angle of incidence is equal to the angle of reflection; (2) the incident ray, the normal to the mirror at the point of incidence, and the reflected ray all lie in the same plane.

Convex mirrors always form an erect image of traffic behind that is smaller than the actual vehicles, and because the mirror curves outward it provides a much wider area of the road behind. This wider field of view helps drivers see more of the road, which is why convex mirrors are also installed at road intersections and sharp bends to prevent collisions.

When an object is placed close to a concave mirror, the image is erect and larger than the object (enlarged). As the object is moved farther away, the image becomes inverted — initially enlarged and then progressively smaller.

A convex lens is thicker at the middle than at the edges and converges (brings together) light beams passing through it. A concave lens is thicker at the edges than in the middle and diverges (spreads apart) light beams. This is why a convex lens is also called a converging lens and a concave lens a diverging lens.

An object viewed through a concave lens always appears erect and diminished in size, regardless of its distance. Through a convex lens, the object appears erect and enlarged when close, but inverted when moved farther away.

Dentists use a concave mirror because, when held close to the teeth, it provides an enlarged erect view of the teeth inside the mouth, making it easier to inspect them.

A concave mirror converges light beams reflected from the Sun, concentrating them at a single bright spot on the paper. Similarly, a convex lens converges sunlight passing through it to a focused point on the paper. In both cases, the concentrated light produces enough heat to ignite the paper.

A solar concentrator is a device that uses mirrors or lenses to concentrate sunlight into a small area. The concentrated sunlight heats a liquid to produce steam, which can generate electricity, provide heat for large-scale cooking, or even melt steel in solar furnaces.

Yes. The laws of reflection are valid for all kinds of mirrors — plane, concave, and convex. However, when multiple parallel rays fall on a spherical mirror, the curved surface causes the reflected rays to converge (for a concave mirror) or diverge (for a convex mirror), even though each individual ray obeys the same laws of reflection.

The warning states 'Objects in mirror are closer than they appear.' Because convex mirrors always form diminished images, objects reflected in them look smaller and therefore appear farther away than they actually are, which is an important safety reminder for drivers.

Lenses are used in eyeglasses to help people see clearly, in cameras, telescopes, and microscopes. The human eye also contains a convex lens that can change its shape to focus on objects at different distances.

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