A warehouse uses a small plane mirror to redirect a barcode scanner beam around a protective box. Fig. 1 is a plan view of the arrangement. The scanner send...
Question 1 Report
A warehouse uses a small plane mirror to redirect a barcode scanner beam around a protective box. Fig. 1 is a plan view of the arrangement. The scanner sends a narrow beam through air to the mirror. The mirror turns the beam towards a label on a moving crate. A normal has been drawn at the point where the light meets the mirror. Angle P is measured between the incident ray and the mirror surface. The rate at which crates pass the scanner is 10 per minute, so the reflected beam must remain correctly aligned.
(a) Calculate the angle of incidence of the scanner beam. [2]
(b) Calculate the angle between the incident ray and the reflected ray. [2]
(c) What rule links the angle of incidence to the angle of reflection? [1]
(d) Draw an arrow on the normal in Fig. 1 to show that the normal is at right angles to the mirror. [1]
(e) Describe how the reflected beam would change if the mirror were rotated clockwise through 5°, while the scanner and crate stayed still. [2]
(f) Use the particle model of light to state why the beam can travel through the air space between the scanner and the mirror. [2]
Answer Details
(a) P is measured between the incident ray and the mirror surface, so it is not the angle of incidence.
\[i=90°-64°=26°\]
The angle of incidence is 26°. [2]
(b) The angle of reflection is also 26°. [1]
\[\text{angle between incident and reflected rays}=26°+26°=52°\]
The angle between the rays is 52°. [2]
(c) The rule is: the angle of incidence equals the angle of reflection. [1]
(d) The normal must be marked as perpendicular to the mirror, using a right-angle mark. [1]
(e) If the mirror rotates clockwise through 5°, the reflected beam also rotates clockwise. [1] It rotates through 10°, twice the mirror rotation, so it may miss the label. [1]
(f) Light is transmitted through air. [1] Air particles do not absorb or block all the light energy, and there is space between particles, so the beam can travel from the scanner to the mirror. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
