The diagram shows the variation with time / of the magnetic flux density B of the field linking a coil - AQA - A-Level Physics - Question 26 - 2020 - Paper 2
Question 26
The diagram shows the variation with time / of the magnetic flux density B of the field linking a coil.
Which graph shows the variation of induced emf ε in the coil ... show full transcript
Worked Solution & Example Answer:The diagram shows the variation with time / of the magnetic flux density B of the field linking a coil - AQA - A-Level Physics - Question 26 - 2020 - Paper 2
Step 1
Identify the relationship between magnetic flux and induced emf
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Answer
The induced emf in a coil is proportional to the rate of change of magnetic flux linking the coil. According to Faraday's law of electromagnetic induction, this is expressed as:
ext{emf} = - rac{d ext{Φ}}{dt}
where ( \text{Φ} ) is the magnetic flux.
Step 2
Analyze the graph of magnetic flux density B
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Answer
From the given graph, we see that the magnetic flux density B changes over time. Specifically:
From time 0 to ( t_1 ), B is constant at 0.
From ( t_1 ) to ( t_2 ), B increases steadily.
After ( t_2 ), B decreases back to 0.
Step 3
Determine the induced emf during each interval
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Answer
From 0 to ( t_1 ): Since B is constant (0), the induced emf is also 0.
From ( t_1 ) to ( t_2 ): As B increases, the rate of change of B is positive, leading to a positive induced emf.
From ( t_2 ) onwards: As B decreases, the rate of change of B is negative, resulting in a negative induced emf.
Step 4
Select the appropriate graph from the options
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Answer
Based on the analysis, the induced emf ε will initially be 0, rise to a positive value, and then drop to a negative value after ( t_2 ). The correct graph that represents this behavior is Graph D.
