While this year’s DSE Physics exam wasn’t much tougher than previous years, a decrease in the number of questions in Paper 1, Section B (structural questions) meant that concepts were tested in more depth, said Vic Chan, a tutor at Modern Education.
This year, there were only nine long questions in Section B, compared with 10 in 2014-15, and 11 in 2012-13.
“In previous years, one question could be worth as few as five marks, but this year the lowest number of marks allocated to a single question was seven,” he tells Young Post. “But at the same time, all of the seven core topics were covered. It meant that you really had to understand the concepts, and know how to apply them to real-life situations.”
Out of the nine questions this year, two were application questions. Question 4 tested students on the mechanics of a jetpack; while Q8 asked students about the electric and magnetic fields involved when lightning occurs. Chan said having background knowledge of how these processes work would greatly help with solving the problems. “For example, if a student knew what a jetpack was – that it rises, then reaches a point where it stops in mid-air – they would know that it’s all about Newton’s Laws.”
Because all the other long questions were straightforward, Chan said the two questions on applications were used to distinguish high-performing students.
Several multiple choice questions in Paper 1 also focused on daily-life applications, said Wayne Leung, a tutor at Beacon College. Many were things that students commonly see, but they might not have thought about the physics concepts involved. For example, Q4 tested understanding of the speedometer of a car, Q19 was about what happens when light passes through a pinhole, and Q28 discussed the carbon dioxide emissions of a television left on stand-by.
Chan said a good strategy for preparing for application questions was to look at what was tested in the multiple choice questions in previous years, because it was likely that those topics would be turned into long questions in the future. “The application of physics in lightning was actually tested in the multiple choice section – Q25 – in 2013. It was a calculation question at the time. So it’s not too difficult to see what will come up next,” he said. “Really, the question setters are kind of lazy.”
As well as looking at multiple choice questions to get an idea of what may be tested in the future, Chan recommends looking at the physics behind various weather phenomenons, sports, roller coasters, and games. “Take Angry Birds for example. Everything behind it is about mechanics. What force you pull, the angle at which you pull. So don’t just play. Think about what physics questions can be asked from it.”
Wong Yiu-fai, vice-principal and physics teacher at Cheung Sha Wan Catholic Secondary School, noted that there were more experiment-based questions. “Questions like Q2 and Q6 in Section B would be very unfamiliar to students who have not done these experiments in the lab. They would easily lose the three marks in Q6. a)i, which is actually a simple calculation. It would also be difficult for them to explain why the experiment had to be set up this way,” he said.
Leung said to improve the accuracy of experiment-based questions which involve plotting graphs, such as Q5 which was about optics, one good strategy is to calculate the answer using equations before drawing the line on the graph. “It asks you to draw the line first before giving the answer, but then your answer could be highly inaccurate,” he explains.
Wong Chi-wai, a teacher at Immaculate Heart of Mary College, said he also observed a trend in assessing students’ skills pinpointing discrepancies between experiment results and theoretical values. In Q7. b)ii, for example, students were asked to calculate the percentage error involved in measuring the resistance of a resistor. “Before, this was usually more a qualitative question of what factors would cause a deviation. It’s rare that students are asked to calculate this.”
Overall, both teachers agreed that this year’s paper was quite straightforward, although there were questions where students had to be careful to avoid traps. For example, Wong Yiu-fai said if students missed the keyword “steadily” in multiple choice Q9, they would have taken into account the length of “z” and worked out the wrong answer. The other two relatively challenging questions were Q22, which was an unusual test on the relation of the speed of an object and its image; and Q26, which assessed students’ concept of one coulomb unit.
“It’s tricky because the energy factors mentioned in the questions are distracting,” he said.
Wong Chi-wai also noted that there were generally fewer calculations-based questions; instead, more questions focused on the concepts behind the calculations. “In the past, students could substitute numbers to test which MC option was right or wrong. Many exercises still stress calculation questions, but it’s actually no longer a focus,” he said.
Wong Yiu-fai noticed that in Paper 2 this was the third time that the photoelectric effect has been tested in the long question format for Section A (Atomic World) in past exam papers and sample papers. “It’s probably because this topic involves lots of topics and calculations, so it’s easy to come up with long questions,” he said.
For Section C (Energy and Use of Energy), he said students needed a firm understanding of graphs in order to do well. “The application of wind power had never been tested so deeply before, there’s a lot of text to read, so it may be time-consuming for students to understand the question and apply the logic required,” he said.
For Section D (Medical Physics), Wong Chi-wai said some the questions were beyond his expectations. Such as multiple choice question Q4.3, which may have been challenging for students who did not study biology because it required knowledge of the structure of the ears, he said. Multiple choice question Q4.7 also required the use of natural logarithms to solve, so students with weaker math skills were at a disadvantage. Some other questions were also tricky because the axis of the graphs had different units, he added, so students had to be careful and know to differentiate that.
Wong Yiu-fai said to get a Level 3, students would need about 50 to 60 per cent of the total. To obtain a Level 5**, they would need at least 87 per cent.