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A student clamped a wire between the poles of a permanent magnet - AQA - GCSE Physics Combined Science - Question 7 - 2020 - Paper 2
Question 7
A student clamped a wire between the poles of a permanent magnet. The student investigated how the force on the wire varied with the current in the wire. Figure 13 s... show full transcript
Worked Solution & Example Answer:A student clamped a wire between the poles of a permanent magnet - AQA - GCSE Physics Combined Science - Question 7 - 2020 - Paper 2
Step 1
When the switch was closed the reading on the top pan balance increased.
Answer
The downward force on the balance increased because there is a current in the wire, producing a magnetic field around the wire. This causes a magnetic force that acts upward on the wire, which is observed as an increase in the balance reading.
Step 2
Explain how the values in Table 3 can be used to determine the size of the force on the wire.
Answer
The difference in mass readings from the top pan balance (254.8 g - 252.3 g = 2.5 g) gives the equivalent weight of the force acting on the wire. Converting this mass to weight involves using the gravitational field strength (approximately 9.8 N/kg), resulting in a force of 0.02375 N (2.5 g = 0.0025 kg; thus, the force = 0.0025 kg × 9.8 N/kg).
Step 3
Determine the magnetic flux density.
Answer
To find the magnetic flux density (B), we can use the formula derived from the gradient of the graph. Given the gradient calculated as 0.031 (from the rise over run), we can express this as:
ext{gradient} = rac{ ext{Force}}{ ext{Current} imes ext{Length}}
Thus, rearranging this gives us:
B = rac{0.031}{0.125} = 0.25 ext{ T}
Therefore, the magnetic flux density is 0.25 T.