Laboratory work. Studying reflection of light with a plane mirror
You need: a plane mirror mounted at the middle of an optical disc (or a mirror standing on paper), a torch or light pointer producing a thin beam (a 3–6 V bulb), thick white paper, a protractor and a ruler. Stand the mirror on a straight line drawn on the paper; at the middle of the line draw its perpendicular (the normal). Aim the torch beam at that point of the mirror: the track of the incident and reflected beams is visible on the paper — mark them with a pencil. Measure the angle of incidence α and the angle of reflection β from the normal with a protractor. Change α to 20°, 40°, 60° and write down β. You will find β ≈ α, and that the incident ray, reflected ray and normal lie in one plane (check by tilting the paper slightly). If the angle of incidence is 0° (ray along the normal), the ray returns along its path: β = 0°. Small differences are measurement error.
Laboratory work (in pairs): measure β for α = 20°, 40°, 60° and tabulate: “α, β, α − β”. Safety: do not aim the beam at anyone’s eyes; if a laser pointer is used, adult supervision; use only a 3–6 V bulb (never mains); handle a glass mirror carefully.