[Physics SPM] Exam Pointers V

Source: Maths & Science Guide

Revision
Explain how upthrust is produced during the flight of an aeroplane. [ 5 marks ]

Frequent Mistakes
Student's Answer:
Upthrust is produced based on the Bernoulli's principle, which states that a low pressure is generated at the point where a fluid travels at high speed. Hence, when the air flows at high speed, a low pressure is generated and subsequently produces a net forces that acts upwards on the aeroplane. This net force constitutes the upthrust.

Comments:
The command word is "explain", and the objective of the question refers to how the upthrust is produced. Since the allocation of marks is five, the answer should consist of five main points. The student has identified the command word as well as the objective of the question. However, the lengthy statements cause the answer to stray away from the objective. Also, even though the answer mentions that air flows at high speed, it does not state where - above or below the wings or body of the aeroplane. Hence, the explanation is inaccurate.

Correct Answers

• The shape of an aeroplane is that of an aerofoil.
• This shape ensures the speed of air is higher above the wings and body of the plane than that under them.
• Based on the Bernoulli's principle, the air pressure under the plane is higher that the above it.
• Hence, a net force that acts upwards is generated on the aeroplane.
• This provides the upthrust that lifts the plane during its flight.

[Physics SPM] Exam Pointers IV

Source: Maths & Science Guide

Revision
State the factors that influence the accuracy of a measurement. [ 4 marks ]

Frequent Mistakes
Student Answers:
Accuracy is evaluated based on how close a quantity's measured value is to its actual value. Accuracy is influenced by the level of error present in the measurement. The presence of error will cause a measured value to deviate from its actual value, thus reducing the accuracy level of measurement. The errors that normally reduce the accuracy of a measurement are parallax error and zero error.

Comments:
Identify the command word "state" and the objective of the question, which focuses on "the factors that influence accuracy". Since the allocation of marks is four, the answer should consist of four main points. The student's lengthy explanation about errors and how they reduce the accuracy of a measurement is not required. It shows that the student does not understand the objective of the question clearly and accurately. Though the answer is full of factual information, it is low quality as it fails to meet the objective of the question.

Correct Answer
Any four of the following:

• The selection of the techniques of measurement.
• Precision of a device.
• Sensitivity of a device.
• The selection of a suitable device based on the size of measurement.
• The presence of error in a device, or due to the experimenter, during a measurement.

[Physics SPM] Exam Pointers III

Source: Maths & Science Guide

Revision

1. Compare the separating distance between consecutive bright fringes of red light with that of blue light of the interference pattern obtained from a Young's double slit experiment.
   
   
2. State one observation of the interference pattern of red light in a Young's double slit experiment.

Frequent Mistakes

Student's answer:

1. The interference of red light has a bigger number of fringes due to the smaller separating distance compared to that of blue light. This is because the wavelength of red light is bigger than that of blue light.
   
   
2. Bright and dark fringes are observed due to the interference of coherent waves.

Correct Answer

1. The separating distance between consecutive bright fringes of red light is bigger than that of blue light.
   
   
2. Alternate bright and dark fringes are formed. The central fringe is the bright fringe. All the fringe sizes are equal, or the separating distance of consecutive fringes is the same.

[Physics SPM] Exam Pointers II

Source: Maths & Science Guide

Revision

1. What are waves?
   
   
2. What is meant by "speed"?

Frequent Mistakes

Student's answers:

• Waves are energy produced by oscillations that is able to transfer through medium and travel through vacuum.

Correct Answers

1. Waves are the propagation of energy through the oscillation of particles of a medium.
   
   
2. It is the rate of change of distance. It is = (distance/time). When an object travels a distance of 20m in 10s, its speed is (20/10) = 2m/s. It is scalar quantity.

Comments:

• The command phrase is "What is meant". Thus, you can choose to give the definition of speed, OR examples that provide the meaning of speed.

[Physics SPM] Exam Pointers I

Source: Maths & Science Guide



Revision

1. Relate the inertia of an object to its mass.
   
   
   
   
2. Why does refraction of water waves occur?
   
   
   
   
3. What is observed when a mercury thermometer is placed in a hot water of 80°C?

Frequent Mistakes



Student's answer:

1. The inertia of an object is directly proportional to its mass.
   
   
   
   
2. When a water wave travels from deep water to shallow water, it undergoes refraction.
   
   
   
   
3. Themal equilibrium is achieved.

Correct Answers

1. The higher the mass, the higher is the inertia.
   
   
   
   
2. Because water waves undergo change in speed in the direction of propagation.
   
   
   
   
3. The mercury length increases to the 80°C mark./The mercury rises up the tube to the 80°C mark.

* Deeper water allows greater velocities while shallower water causes lower velocities.