The method and the results are on the reflection of light lab. Do the analysis yourself first, then check the answers below.
Quick answer: Light is reflected, refracted or absorbed when it meets matter. These answers go with the grade 7 science lab on reflection of light: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
The sample readings show reflection angles within 1° of the incidence angles, and refraction angles smaller than the incidence angles. Use these model answers to check your own analysis and graph.
The points lie close to a straight line through the origin. Gradient = (74 – 16) ÷ (75 – 15) = 58 ÷ 60 = 0.97, about 1.0.
Question 3 Conclusion
r is equal to i within about 1°, so the measurements support the law of reflection. i = r
Question 4 Uncertainty
The differences (±1°) are the same size as the reading uncertainty, so they are measurement errors, not a failure of the law. Within uncertainty, i = r.
Question 5 Refraction results
20 – 13 = 7°; 40 – 25 = 15°; 60 – 35 = 25°. The ray always bends towards the normal and the bend grows as i grows. 7°, 15°, 25°
Question 6 Prediction
50° is halfway between 40° and 60°, so r is about halfway between 25° and 35°, that is (25 + 35) ÷ 2 = 30°.
Question 7 Light speed
Light travels more slowly in the block than in air, so the ray changes direction towards the normal on entering. Slower speed gives bending towards the normal.
Question 8 Improvement
Use a narrower ray; place the dots farther apart; use a larger protractor; repeat each angle and take the mean. A narrower ray and repeats.
