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In an experiment to verify Snell's law, a student recorded the following data - Leaving Cert Physics - Question 3 - 2010
Question 3
In an experiment to verify Snell's law, a student recorded the following data. | i/° | 30 | 40 | 50 | 55 | 60 | 65 | 70 | |-----|----|----|----|----|----|----|----|... show full transcript
Worked Solution & Example Answer:In an experiment to verify Snell's law, a student recorded the following data - Leaving Cert Physics - Question 3 - 2010
Step 1
Draw a labelled diagram of the apparatus used.
Answer
To draw a labelled diagram for the experiment verifying Snell's law:
- Apparatus Setup: Start by illustrating the ray box or light source that emits rays of light.
- Water or Glass Block: Depict a block representing the medium where refraction occurs. This could be an aquarium or a glass block.
- Protractor Placement: Show a protractor aligned with the normal line at the point where light enters the medium.
- Incident Ray (i): Draw an incident ray hitting the interface at angle 'i' measured from the normal.
- Refracted Ray (r): Draw the refracted ray emerging from the block at angle 'r' measured from the normal.
- Label Parts: Clearly label the source, the medium, angles i and r, and the normal line.
Step 2
Using the recorded data, draw a suitable graph and explain how your graph verifies Snell's law.
Answer
To verify Snell's law using the recorded data:
- Graph Setup: Plot a graph with angle i (degrees) on the x-axis and angle r (degrees) on the y-axis.
- Data Points: Use the data provided:
- (30, 19)
- (40, 26)
- (50, 30)
- (55, 33)
- (60, 36)
- (65, 38)
- (70, 40)
- Plotting Points: Mark each of the data points on the graph paper.
- Line of Best Fit: Draw a straight line through the points to show their relationship.
- Explanation: The linearity of the plotted points demonstrates that as the angle of incidence increases, the angle of refraction also increases. This confirms Snell's law, which can be expressed as illustrated by the straight line indicating a proportional relationship between i and r.
Step 3
Using your graph, calculate the refractive index of the substance used in the experiment.
Answer
To calculate the refractive index using the graph:
- Select Angles: Choose two pairs of angles from the graph that clearly represent the relationship, for instance (30°, 19°) and (60°, 36°).
- Applying Snell’s Law: Use Snell's law to calculate the indices:
Assuming the incident medium is air (n1 = 1), we can use the equation:
For angle pairs:
- For (30°, 19°):
- For (60°, 36°):
- For (30°, 19°):
- Average Index: Take an average of the refractive indices calculated to arrive at an overall index for the medium.
Step 4
The student did not record any values of the angle i below 30°. Give two reasons why.
Answer
Reasons for not recording values below 30°:
- Total Internal Reflection: At angles of incidence below a certain critical angle, total internal reflection may not occur, which means that the angles below 30° may not yield useful refraction data, making it difficult to measure accurately.
- Measurement Limitations: The apparatus used may have a physical limitation or design flaw that prevents accurate readings at lower angles, affecting the reliability of the data at these values.