Alternative B
Question 2B
You are provided with plane mirror, drawing board, plain sheets, optical pins and other necessary apparatus.
Using the diagram above as a guide to perform the experiment.
(i) Fix the drawing paper to the drawing board.
(ii) Place the mirror vertically with its longer side resting on the drawing paper. Draw a straight line AB to represent the reflecting surface of the mirror. Remove the mirror.
(iii) Draw a normal NQ to meet AB at its midpoint Q
(iv) Draw a straight line ST through A, to meet AB at right angle.
(v) Measure a distance AC = X = 1.5 cm
(vi) Draw a line CQ to represent an incident ray. Place two optical pins P1 and P2 on CQ.
(vii) Replace the mirror on AB.
(viii) Place two other pins, P3 and P4 to be in a straight line with the images of P1 P2.
(ix) Remove the mirror and the pins.
(x) Draw a straight line through the positions P3 and P4 to meet AB at Q.
(xi) Measure and record angle ACQ as θ1 and angle CQN as θ2
(xii) Evaluate x-1 and tan θ2
(xiii) Repeat the procedure for four other values of x = 2.5 cm, 3.5 cm, 4.5 cm and 6.0 cm.
(xiv) Tabulate your results.
(xv) Plot a graph, with tan θ2 on the vertical axis and x-1 on the horizontal axis.
(xvi) Determine the slope, s, of the graph.
(xvii) State two precautions taken to ensure accurate result. (Attach your traces to your booklet.)
(b)(i) Distinguish between regular and diffused reflections.
(ii) An object is placed 25 cm in front of a plane mirror. Determine the distance of the image from the object and the size of the images relative to the object.
Observation
The expected response:
- Five complete traces showing at least AB perpendicular to ST, NQ perpendicular to AB, CQ and QR
- Five values of x correctly measured and recorded to at least 1d.p in cm
Five values of θ1 correctly measured and recorded in degrees and in trend
- Five values of θ2 correctly measured and recorded in degrees and in trend
- Five values of x-1 correctly evaluated to at least 3d.p
- Five values of tan θ2 correctly evaluated to at least 3 s.f
- Composite table showing at least x-1, θ1, θ2, x-1 and tan θ2
- Both axes correctly distinguished
- Plot a graph using reasonable scales
- Draw line of best fit
- Determine the slope of the graph
- State any two of the following precautions.
e.g.
- Neat traces/sharp pencil (seen in traces)
- Ensured pins were vertical/upright/erect
- Repeated readings shown on table
- Avoided parallax error in reading protractor/metre rule
- Noted/Corrected zero error on metre rule
- Reasonable spacing of pins (about 4 cm apart)
b(i) (α) Regular reflection occurs when light falls on a smooth (glass) surface while diffused reflection occurs when light falls on a rough surface
In regular reflection incident parallel rays are parallel after reflection while in diffuse reflection incident parallel rays are scattered after reflection
