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The maximum power of the TENS machine is 240 mW - AQA - GCSE Physics Combined Science - Question 5 - 2021 - Paper 1
Question 5
The maximum power of the TENS machine is 240 mW. The potential difference across the battery in the TENS machine is 2.5 V. Calculate the maximum current from the ba... show full transcript
Worked Solution & Example Answer:The maximum power of the TENS machine is 240 mW - AQA - GCSE Physics Combined Science - Question 5 - 2021 - Paper 1
Step 1
Calculate the maximum current from the battery.
Answer
To calculate the maximum current ( I_{max} ) from the battery, we use the formula:
Where:
- P is the power (in watts)
- V is the potential difference (in volts)
- I is the current (in amperes)
Rearranging gives: Substituting the known values:
Step 2
How does Figure 9 show that the student was not correct?
Answer
The student concluded that there was an alternating potential difference across the electrodes. However, Figure 9 demonstrates that the potential difference remains always positive, indicating that it does not reverse direction. This disproves the student's claim of an alternating potential difference since an alternating current would show both positive and negative values.
Step 3
Step 4
Compare the readings on the voltmeter and ammeter in circuit A and circuit B.
Answer
The voltmeter reading is the same in both circuits because the resistors have the same resistance. However, the ammeter reading in circuit B is twice the reading of circuit A, indicating that the total current flowing through circuit B is greater than that of circuit A.