Investigating Reflection | Physics for GCSE/IGCSE - Year 11 PDF Download

Investigating Reflection

Aims of the Experiment

• To investigate reflection by a plane mirror

Variables

• Independent variable = angle of incidence, i
• Dependent variable = angle of reflection, r
• Control variables:
  • Distance of ray box from mirror
  • Width of the light beam
  • Same frequency / wavelength of the light

Method

Apparatus to investigate reflection

• Set up the apparatus as shown in the diagram
• In the middle of the paper, use a ruler to mark a straight line of about 10 cm long
• Use a protractor to draw a 90-degree line that bisects (cuts in half) the 10 cm line
• Place the mirror on the first line as shown in the diagram above
• Switch on the ray box and aim a beam of light at the point where the two drawn lines cross at an angle
• Use the pencil to mark two positions of the light beam:
  • A point just after leaving the ray box
  • The point on the reflected beam about 10 cm away from the mirror
• Begin by marking two key points: one just after leaving the ray box and the other about 10 cm away from the mirror on the reflected beam.
• Remove the ray box and mirror, then use a ruler to connect the marked positions to where the original lines intersected.
• Utilize a protractor to measure the angles from the 90° line. The angle towards the mirror is the angle of incidence, while the other is the angle of reflection.
• Repeat the experiment thrice with light beams aimed at different angles.

Data Collection Table Example

Analysis of Results

The law of reflection states that the angle of incidence (i) is equal to the angle of reflection (r).
Where:

• i = angle of incidence in degrees (°)
• r = angle of reflection in degrees (°)

If conducted accurately, the angles of incidence and reflection should be identical:

Evaluating the Experiment

Systematic Errors

• An error might arise if the 90-degree lines are inaccurately drawn. It is advisable to use a set square for drawing perpendicular lines.
• Ensure the mirror is free from distortions as this could impact the reflection angle. It's crucial to have a mirror with minimal blemishes.

Random Errors

• Be cautious about marking points for the incoming and reflected beam accurately. To improve accuracy, use a sharpened pencil and mark precisely in the middle of the beam.
• When facing challenges in reading angles accurately due to protractor resolution, opt for a protractor with a higher resolution for better precision.

Important Safety Precautions

• The ray box light could cause burns if touched. In case of burns, run burns under cold running water for at least five minutes.
• Avoid looking directly into the light as it may damage the eyes. Always stand behind the ray box during the experiment.
• Keep all liquids away from the electrical equipment and paper.
• Take care when using the mirror as damages on the mirror can affect the outcome of the reflection experiment.