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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 bat... 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 Maximum Current
Answer
To calculate the maximum current, we can use the formula for power:
where:
- is the power in watts (W).
- is the potential difference in volts (V).
- is the current in amperes (A).
Given that the power is 240 mW, we can convert that to watts:
Now we can rearrange the formula to solve for current:
Calculating this gives us:
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 illustrates a waveform that is always positive, indicating that the potential difference does not change direction. This suggests a direct current (DC) rather than an alternating current (AC).
Step 3
Step 4
Compare the readings on the voltmeter and ammeter in Circuit A and Circuit B.
Answer
For the voltmeter: The reading is the same in both circuits since the voltage across the components remains unchanged.
For the ammeter: The reading in Circuit B is twice the reading of Circuit A, indicating that Circuit B has a lower total resistance, resulting in higher current flow.