Question

Describe an experiment to verify the laws of reflection of light. [$\text{4 Marks}$]

Answer 1

(i) Take a wooden drawing board and fix a white sheet of paper on it.
(ii) On the paper draw a straight-line ${\text{MM}}^{\prime }$ .
(iii) Mark a point $\text{O}$ on its middle. Draw a line $\text{OA}$ such that $\angle \text{MOA}$ is less than ${90}^{\circ }$ . Draw a normal $\text{ON}$ at point $\text{O}$.
(iv) Place a mirror on line ${\text{MM}}^{\prime }$ such that the polished side of the mirror is along the line. Hold the mirror in the mirror holder.
(v) Fix two steel pins $\text{P}$ and $\text{Q}$ on the straightline $\text{OA}$ at least $10cm$ apart.
(vi) Set your eye on the other side of the normal ON. You will see the images ${\text{P}}^{\prime }$ and ${\text{Q}}^{\prime }$ of the pins $\text{P}$ and $\text{Q}$ in the mirror.
(vii) Set your eye in line with the two images ${\text{P}}^{\prime }$ and ${\text{Q}}^{\prime }$ and fix two more pins $\text{R}$ and $\text{S}$ on the paper in front of the mirror such that both are in line with ${\text{P}}^{\prime }$ and ${\text{Q}}^{\prime }$.
(viii) Now remove the mirror. Draw small circles around the pins $\text{P}$, $\text{Q}$, $\text{R}$ and $\text{S}$ to mark their positions.
(ix) Draw a line $\text{OB}$ joining the points $\text{R}$ and $\text{S}$.
$\text{AO}$ = Incident ray
$\text{OB}$ = Reflected ray
$\text{ON}$ = Normal ray
(x) Now using a protractor, measure the angle $i=\angle \text{AON}$ and $r=\angle \text{BON}$. You will find the two angles are equal.
(xi) Since the incident ray normal and reflected ray, all lie in the same plane of the paper, this verifies the second law of reflection.
Theory Explanation [$\text{3 Marks}$]
Diagram [$\text{1 Mark}$]