This experiment verifies the laws of reflection using a plane mirror and determines the relationship between the angle of incidence and the angle of reflection.
What This Experiment Demonstrates
Verification of the laws of reflection
Equality of angle of incidence and angle of reflection
Graphical relationship between incident and reflected angles
Apparatus Required
Plane mirror with holder
White drawing sheet
Optical pins (at least 4)
Protractor
Ruler
Pencil
Theory
When light strikes a reflecting surface, it obeys the laws of reflection:
The incident ray, reflected ray, and the normal lie in the same plane.
The angle of incidence equals the angle of reflection.
Mathematically, this can be written as:
\[ i = r \]
where \( i \) is the angle of incidence and \( r \) is the angle of reflection.
Method
Fix a white sheet of paper on a drawing board.
Draw a straight line and place the plane mirror vertically along it.
Mark a point on the paper and draw a normal to the mirror at that point.
Draw an incident ray making a known angle \( i \) with the normal.
Place two pins along the incident ray.
Looking into the mirror, place two more pins such that they align with the images of the first two pins.
Remove the mirror and draw the reflected ray through the second pair of pins.
Measure the angle of reflection \( r \) using a protractor.
Repeat the experiment for different values of angle of incidence.
Observations
Record values of angle of incidence and angle of reflection in a table.
Angle of incidence \( i \)
Angle of reflection \( r \)
Graph
Plot a graph of angle of reflection \( r \) (y-axis) against angle of incidence \( i \) (x-axis).
The graph should be a straight line passing through the origin with slope approximately equal to 1.
For guidance on plotting graphs and determining gradients accurately, visit our Graph Guide.
Calculations
From the graph:
\[ r = mi + c \]
where the slope \( m \approx 1 \) and intercept \( c \approx 0 \), confirming the law of reflection.
Result
The experiment verifies that the angle of incidence is equal to the angle of reflection, confirming the laws of reflection.
Sources of Error & Precautions
Ensure the mirror is placed perfectly vertical.
Avoid parallax while aligning pins.
Use sharp pins for better accuracy.
Measure angles carefully using the protractor.
Video Demonstration
Video courtesy of TeagueTube (YouTube). Used for educational purposes under YouTube’s embedding policy.