P6 Science Prelims (NYPS/2023/Booklet B/Q39): Energy (Light)
4 mark question
Science | P6, Prelims (NYPS/2023/Booklet B/ Q39) | Energy
Let’s go through this fun and interesting question on light! Shooting bullets can be fun, but when we track the shots fired using light alone, how does it work, and is it accurate enough? Let’s find out!
The Question (4 marks)
Bala set up a light source and a light sensor to count the number of rubber bullets going through a hole in the cardboard as shown below.
He shot the rubber bullets one at a time and recorded the results in the graph below.
(a) Based on the graph, how many bullets went through the hole in the first 8s? [1]
(b) Explain how Bala could count the number of bullets going through the hole using this setup [2]
(c) Give a possible reason why Bala’s setup may not have been able to accurately count all the bullets that he fired through the hole. [1]
Let’s answer the question!
(a) Explanation: From the graph, we can observe how many times the light sensor detected a drop to zero. These drops indicate the moments when the bullets passed through the hole, blocking the light as they crossed the sensor. Based on the graph, we can identify four instances where this occurred: at 1s, 3s, 5s, and 7s.
Ans: 4 bullets went through the hole in the first 8s.
(b) Explanation: This is a 2-mark question. We need to focus on (1) How this set-up works for detection and (2) How the result would be recorded in the graph
Ans: When bullets pass through the hole, they (1) block the light from reaching the sensor, causing the amount of light detected to drop to zero. By (2) counting how many times the light drops to zero on the graph, Bala can accurately determine the number of bullets that passed through.
(c) Explanation: It is common for kids to press on the trigger in rapid fire, resulting in 2 bullets being detected as one. It is also possible that some bullets may not have travelled straight through the lighted area. With these possibilities, we can explain one possible reason why this set-up may not be able to detect every single bullet that went through the hole.
Ans: A bullet can pass through the hole without travelling past and blocking the light source, in which case it won't be recorded on the graph.