AQA GCSE Combined Science: Trilogy Physics Paper 2 (Foundation), November 2020: Question 2
10 marks · Low Demand difficulty · Short Answer
Explain the role and behavior of springs under computer keyboard keys, convert compression distance units, calculate the compression force, and suggest modifications to close the switch more quickly.
Practise this questionQuestion
Question text
02 Figure 3 shows a computer keyboard.
There is a spring under each key.
Figure 3
02.1 Why do the keys have springs under them?
[1 mark]
Tick ( ) one box.
Springs make the keys easier to press.
Springs make the keys lighter.
Springs push the keys back to their original position.
02.2 Why does every spring used in the keyboard have the same spring constant?
[1 mark]
Tick ( ) one box.
So that more than one key can be pressed at the same time.
So that the same force is needed to press each key.
So that the springs are all the same length.8
Figure 4 shows one of the keys and its spring.
Figure 4
02.3 What happens to the length of the spring when the key is pressed?
[1 mark]
02.4 How far must the key move before it touches the switch?
[1 mark]
Tick ( ) one box.
4.0 mm 4.0 cm 4.0 μm
02.5 If a key is not pressed with enough force, no signal is sent to the computer.
Explain why.
[2 marks]
02.6 The spring in Figure 4 has a spring constant of 200 N/m
Calculate the force on the spring when the key moves a distance of 0.0040 m
Use the equation:
*08* force = spring constant × compression
[2 marks]
Force = N
02.7 Suggest two ways the spring in the key in Figure 4 could be changed so that the
switch can be closed more quickly.
[2 marks]
Mark scheme
Show the mark scheme
AO /
question Answers Extra information Mark
Spec. Ref.
02.1 springs push the keys back to 1 AO1
their original position
6.5.3
02.2 so that the same force is 1 AO3
needed to press each key 6.5.3
02.3 (the length) decreases allow the spring compresses 1 AO1
6.5.3
02.4 4.0 mm 1 AO2
6.5.3
02.5 the spring/key will not move far 1 AO3
enough 6.5.3
so will not press the (electrical 1
contact) switch
02.6 F = 200 × 0.0040 1 AO2
6.5.3
F = 0.80 (N) allow 0.8 (N) 1
02.7 shorter spring 1 AO3
6.5.3
spring with a lower spring allow spring that requires less 1
constant force to compress
allow weaker spring
allow spring that is easier to
compress
Total 10
How to answer it
Forces and Elasticity: Keyboard Springs
This question assesses fundamental ideas from AQA GCSE Physics: Forces and Elasticity (Topic 6.5.3) using an everyday keyboard mechanism:
- Understanding the function of springs in returning objects to their original position.
- The physical meaning of the spring constant (stiffness and force required).
- Converting metric units of distance ( m to mm ).
- Applying cause-and-effect reasoning to complete an electrical circuit.
- Calculating force using the given equation: force = spring constant × compression .
- Evaluating how spring dimensions and properties affect mechanical response time.
Purpose of the Spring
Why do the keys have springs under them?
✅ Correct Answer
Tick option 3:
"Springs push the keys back to their original position."
💡 Key Knowledge
When an elastic object like a spring is compressed, it stores elastic potential energy. When released, this stored energy exerts an restoring force that pushes the key back up to its starting position.
Uniform Spring Constant
Why does every spring used in the keyboard have the same spring constant?
✅ Correct Answer
Tick option 2:
"So that the same force is needed to press each key."
❌ Common Errors
Students often tick "So that the springs are all the same length." Length and spring constant are different properties—springs can be the same length but have completely different stiffnesses!
Effect on Spring Length
What happens to the length of the spring when the key is pressed?
✅ Correct Answer
(The length) decreases
Also allowed: The spring compresses / gets shorter.
🧠 Exam Technique
Keep your answer concise. A single clear word like "decreases" or "shortens" gets the mark immediately without risking contradictory details.
Unit Conversion: Travel Distance
How far must the key move before it touches the switch?
✅ Correct Answer
Tick option 1:
4.0 mm
📐 Unit Conversion Step
Figure 4 shows a gap of 0.0040 m .
To convert metres ( m ) to millimetres ( mm ), multiply by 1000:
0.0040 m × 1000 = 4.0 mm
Insufficient Force Explanation
If a key is not pressed with enough force, no signal is sent to the computer. Explain why.
✅ Correct Answer (Mark Scheme Breakdown)
- Mark 1: The spring/key will not move far enough (does not compress sufficiently).
- Mark 2: So it will not press / touch the electrical contact switch (circuit does not close).
🧠 Exam Technique: Two-Step Logic
For a 2-mark "Explain why" question, structure your answer with a cause and an effect:
Cause: Not enough compression / distance travelled (< 0.0040 m) →
Effect: The switch contacts do not touch, so no circuit is completed.
Calculation: Force on the Spring
Calculate the force on the spring when the key moves a distance of 0.0040 m (k = 200 N/m).
📐 Step-by-Step Calculation
Step 1: State the values from the question
• Spring constant ( k ) = 200 N/m
• Compression ( e ) = 0.0040 m
Step 2: Substitute into the given formula
force = 200 × 0.0040 [1 mark]
Step 3: Calculate the final value
force = 0.80 N (or 0.8 N ) [1 mark]
❌ Common Errors
- Dividing instead of multiplying: Calculating 200 / 0.0040 . Always follow the supplied equation: force = k × compression .
- Incorrect decimal placement: Punching extra zeros into the calculator resulting in 0.08 N .
Improving Switch Response Speed
Suggest two ways the spring in the key in Figure 4 could be changed so that the switch can be closed more quickly.
✅ Correct Answer (Any TWO of the following)
- Shorter spring (means less distance to travel before contacting the switch). [1 mark]
- Spring with a lower spring constant [1 mark]
Alternative phrasing accepted for point 2: a weaker spring / easier to compress / spring that requires less force to compress.
💡 Why these changes work
- A lower spring constant means less force is required to achieve the same compression, so your finger accelerates the key faster.
- A shorter spring places the base of the key closer to the contact pad, reducing travel distance.
Topics
Physics · P5: Forces
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 2 (Foundation), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.