Light

Investigate the reflection of light by different types of surfaces and the refraction of light by different substances.

During this required practical, students will use a ray box to produce a narrow beam of light to trace the path of light when it is reflected from and refracted through blocks made of different materials (e.g. Perspex and glass). They will compare this between the different materials available. Low light conditions are required for this practical procedure.

Equipment (per pair of participants)

• Ray optics box
• Bench power supply
• Rectangular glass block
• Rectangular Perspex block
• 30cm ruler
• Protractor
• Plain A3 paper

Method

Students should use the ruler to draw a straight line in the middle of their paper.
Students should line up their block of material with this centre line and draw around it, to ensure block placement remains the same throughout.
A protractor is used to draw another line at a 90-degree angle to the original line, roughly at the centre of the block. This line is labelled ‘N’ and will be used to centre the beam of light from the ray box.
The students now set up their ray box so that a narrow beam of light is produced.
The ray box should be positioned so that the beam of light meets where the ‘N’ line meets the block. The ray box should be positioned at a distance so that the beam exiting the block is narrow.
The path of incoming light is marked with a series of crosses, and the same is done for the position that the light beam leaves the other side of the block.
The ray box can then be switched off to prevent unnecessary heat. The block is then removed and the crosses are joined up with solid likes to show the path of the three different rays (going into, through; and out of the block).
These rays should be labelled with their scientific names.
A protractor is then used to measure the angles of incidence, reflection and refraction and measurements are recorded in a suitable table.
The method above is then repeated using a block which is made of a different material.

Technician tips

Low light conditions are preferable for this practical. Total black-out should not be required.
In order to improve visibility for students, a large box could be placed over the ray box and paper whilst the students take their measurements. Large printer paper boxes are ideal for this.