Edexcel iGCSE Physics -3.17 Core Practical: Refraction of Light- Study Notes- New Syllabus

Practical: Investigating the Refraction of Light

Refraction is the change in direction of light when it passes from one medium to another due to a change in speed. This practical investigates refraction using different glass shapes to observe how light behaves at boundaries.

Aim

To investigate how light is refracted when it passes through:

• a rectangular glass block
• a semi-circular glass block
• a triangular glass prism

Apparatus

• Ray box with narrow slit 
• Rectangular glass block
• Semi-circular glass block
• Triangular glass prism
• White paper
• Ruler
• Protractor
• Pencil

Relevant Formula

Refraction is explained using the wave equation:

\( \mathrm{v = f\lambda} \)

• When light enters glass, speed decreases.
• Frequency remains constant.
• Wavelength decreases.

Method A: Rectangular Glass Block

• Place the rectangular glass block on white paper and trace its outline.
• Draw a normal at one face of the block.
• Shine a narrow ray of light at an angle into the block.
• Mark the incident ray, refracted ray, and emergent ray.
• Remove the block and complete the ray paths.
• Measure the angle of incidence and angle of refraction.

Observation:

• The ray bends towards the normal on entering the block.
• The ray bends away from the normal on leaving the block.
• The emergent ray is parallel to the incident ray.

Method B: Semi-Circular Glass Block

• Place the semi-circular block flat side down on paper.
• Shine the ray through the curved surface towards the flat face.
• Ensure the ray enters through the curved face along the radius.
• Trace the incident and refracted rays.
• Measure angles at the flat surface.

Observation:

• No refraction occurs at the curved surface.
• Refraction occurs only at the flat surface.
• This allows accurate measurement of refraction.

Method C: Triangular Prism

• Place the triangular prism on paper and trace around it.
• Shine a narrow ray into one face of the prism.
• Trace the ray as it enters and exits the prism.
• Observe the bending of the ray.

Observation:

• The ray is refracted at both faces of the prism.
• The overall direction of the ray changes.
• White light spreads into colours (dispersion).

Results and Conclusions

• Light bends when it enters a medium with a different optical density.
• The direction of bending depends on whether light speeds up or slows down.
• Different shapes help observe refraction more clearly.

Sources of Error

• Thick pencil lines.
• Inaccurate protractor readings.
• Misalignment of ray box.

Improvements

• Use a thinner beam of light.
• Repeat readings and take averages.
• Ensure the block does not move during tracing.

Key Idea

• Refraction occurs when light changes speed.
• Glass causes light to slow down.
• Different block shapes demonstrate refraction clearly.