Geometric Optics practice quiz

Key ideaThe angle of incidence equals the angle of reflection, both measured from the normal.

Common mistakeMeasuring the angles from the surface instead of the normal.

Key idean₁ sin θ₁ = n₂ sin θ₂. Light bends toward the normal entering a medium with a higher n, and total internal reflection can only happen going toward a lower n.

Common mistakeBending the ray the wrong way, or expecting total internal reflection when going into a medium with a higher n.

Key idea1/f = 1/d_o + 1/d_i with f = R/2. A real image (d_i > 0) is inverted, and a convex mirror always forms a virtual, upright, smaller image.

Common mistakeSign errors for virtual images or convex mirrors (negative d_i and f).

Key ideaThe thin-lens equation is 1/f = 1/d_o + 1/d_i. A converging lens with the object outside f gives a real, inverted image; inside f it gives a virtual, upright, enlarged one.

Common mistakeTreating a diverging lens’s focal length as positive.