Master the laws of reflection and refraction, use the mirror and lens formulas, and understand refractive index.
The angle of incidence always equals the angle of reflection. For spherical mirrors, the mirror formula relates object distance (u), image distance (v), and focal length (f):
An object is placed at the centre of curvature of a concave mirror (u = −30 cm, f = −15 cm). Find v using the mirror formula.
v = −30 cm — the image also forms at the centre of curvature, same size, inverted
Light bends when it passes between media of different density. The refractive index describes how much it bends:
Is the refractive index of glass with respect to air greater than, less than, or equal to 1?
Greater than 1 — glass is optically denser than air, so light bends toward the normal entering it
Convex lenses converge light and have a positive focal length; concave lenses diverge light and have a negative focal length. The lens formula is similar to the mirror formula:
Does a convex lens converge or diverge parallel light rays?
Converges them — that's why it's called a converging lens
1. State the law of reflection in one sentence.
2. A concave mirror has f = −20 cm and an object is placed at u = −40 cm. Find v using 1/v + 1/u = 1/f.
3. Is the refractive index of a medium ever less than 1 (compared to vacuum)?
4. Does a concave lens form a real or virtual image of a distant object?
5. Which type of lens is used to correct nearsightedness?