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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... 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. Explain why the increased reading showed that there was an upward force on the wire.
Answer
When the switch is closed, a current flows through the wire, which creates a magnetic field around it. According to the principles of electromagnetism, this magnetic field interacts with the magnetic field of the permanent magnet. The interaction generates a magnetic force on the wire, which acts in an upward direction, counterbalancing the weight of the wire, hence the top pan balance reading increases.
Step 2
Explain how the values in Table 3 can be used to determine the size of the force on the wire.
Answer
The values in Table 3 show the mass readings of the top pan balance when the switch is open and closed. The difference between these two readings indicates the force acting on the wire. Specifically, the reading when closed (254.8 g) minus the reading when open (252.3 g) gives a change of 2.5 g. To convert this mass difference to force, it is multiplied by the gravitational field strength (approximately 9.8 m/s²). The force can therefore be calculated as:
F = rac{2.5 ext{ g}}{1000} imes 9.8 ext{ m/s}^2 = 0.02375 ext{ N}
Step 3
Determine the magnetic flux density.
Answer
To determine the magnetic flux density (B), we use the formula relating force (F), current (I), length of wire (L), and the magnetic flux density:
From the graph (Figure 14), we can find the gradient, which represents ( \frac{F}{I} ). Assuming we calculated the gradient to be 0.031, we can rearrange the formula to find B:
- Calculate B using ( B = \frac{F}{I \times L} ) with ( L = 0.125 m ).
- Substituting the values:
Thus, the magnetic flux density is 0.25 T.