Investigating reflection of light off a plane mirror
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Summary
Investigating reflection of light off a plane mirror
In a nutshell
By using a ray box and a plane mirror, you will investigate the law of reflection for light. You will do this by measuring the angle of incidence and reflection for a light wave reflecting off a plane mirror.
Equipment list
The following equipment list can be used to conduct the experiment to investigate reflection by a plane mirror.
Equipment | Use |
| Ray box and single slit grating | To create a narrow beam of light. |
| Power supply | To provide power for the ray box. |
| Plane mirror | To reflect the light ray. |
| Paper | To show the direction of the light ray. |
| Pencil | To mark the direction of the light ray. |
| Ruler | To ensure the lines of the light ray are drawn straight. |
| Protractor | To measure the angles of the light ray. |
Experimental variables
The independent variable is the variable you change. The dependent variable is the variable that changes depending on the other variables, and is the one you measure. The control variables are the variables that are kept constant.
| Independent Variable | |
| Dependent Variable | |
| Control Variables | |
Safety precautions
When performing experiments, it is very important to consider safety precautions. This is so that no one gets hurt or injured during the experiment.
Hazard | Risk | Safety Measure |
| Ray box | The box gets very hot and could result in a burn. | Do not touch during use or straight after use. Leave it to cool before putting it away. If burnt, run burns under cold water. |
| Light ray | Looking into the light may damage eyes. | Don't look directly at the light. Keep the ray box directed away from you. |
| Dark room | There may be trip hazards that are difficult to see due to the lack of light | Take care when moving about, and try to limit movement. Check for hazards before dimming lights. |
Method
These are the instructions to complete the experiment. Record all measurements taken as you work through the experiment in a table.
 |
|
| 1. | Set up the apparatus as shown in the diagram. The mirror should be placed on top of the sheet of paper. |
| 2. | Draw pencil lines around the edge of the mirror. This means it can be placed back if anything goes wrong. |
| 3. | Switch the ray box on and direct the light ray at the mirror. |
| 4. | Using the protractor, draw a line at to the mirror's surface, where the light ray hits it. This is the normal. |
| 5. | Position the ray box so that it makes an angle with the normal (angle of incidence). |
| 6. | Mark on the paper:
|
| 7. | Remove the mirror and, using a ruler, join up these lines to trace the outline of the light ray. |
| 8. | Measure the angles of incidence and reflection using a protractor. |
| 9. | Repeat steps 5-8 for at least two more angles of incidence. |
Analysis
This is how you will use the data recorded to form conclusions.
| 1. | Compare the angles of incidence and reflection. |
| 2. | Compare these to known theory (the law of reflection). The angle of incidence and reflection should be the same for all angles of incidence. |
Conclusion
The results from your experiment should confirm the law of reflection. This would mean the angle of incidence and reflection should be the same for all angles of incidence.
Evaluation
Once you have completed your experiment, it is important to consider how it could be improved. You should come up with ways to improve the accuracy of your values. If you got a result that seems unreasonable, think about why this was.
FAQs - Frequently Asked Questions
What is the law of reflection?
The law of reflection states the angle of incidence and reflection should be the same for all angles of incidence.
How do you investigate reflection?
By using a ray box and a plane mirror, you can investigate how the law of reflection for light. You can do this by measuring the angle of incidence and reflection for a light wave reflecting off a plane mirror.