9702 · 20.5
Electromagnetic induction flashcards
Revision flashcards for Cambridge 9702 Electromagnetic induction (syllabus 20.5). Flip, recall, then mark a real past-paper question.
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What is electromagnetic induction?
The process of generating an electromotive force (EMF) in a conductor due to a changing magnetic field or relative motion.
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Define magnetic flux ($\Phi$) and its SI unit.
Magnetic flux is the measure of the total magnetic field lines passing perpendicularly through a given area. Its SI unit is the Weber (Wb).
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How is magnetic flux calculated?
$\Phi = BA \cos \theta$, where B is magnetic flux density, A is the area, and $\theta$ is the angle between the field and the normal to the area.
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What is magnetic flux linkage ($\lambda$)?
The total magnetic flux interacting with all turns of a coil. For N turns, $\lambda = N\Phi$.
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State Faraday's Law of Electromagnetic Induction.
The magnitude of the induced EMF is directly proportional to the rate of change of magnetic flux linkage.
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What is the formula for the magnitude of induced EMF?
$\mathcal{E} = |\frac{\Delta (N\Phi)}{\Delta t}|$ or $\mathcal{E} = |\frac{\Delta \lambda}{\Delta t}|$.
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What is the main idea behind Lenz's Law?
The induced current's magnetic field always opposes the change in magnetic flux that caused it.
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What does the negative sign in $\mathcal{E} = -\frac{\Delta (N\Phi)}{\Delta t}$ represent?
It explicitly indicates the opposing nature of the induced EMF, as described by Lenz's Law.
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Briefly explain the Hall Effect.
A potential difference (Hall Voltage) is induced across a current-carrying conductor when placed in a perpendicular magnetic field, due to charge carrier separation.
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What is a Hall Probe used for?
It's a device that uses the Hall Effect to accurately measure magnetic flux density.
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What is the formula for the motional EMF induced in a straight conductor moving perpendicularly through a uniform magnetic field?
$\mathcal{E} = BLv$, where B is the magnetic flux density, L is the length of the conductor, and v is its speed.
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How can the magnitude of the induced EMF in a rotating coil be increased?
By increasing the number of turns (N), the magnetic field strength (B), the area of the coil (A), or the angular speed of rotation (ω).
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What is the purpose of a laminated soft iron core in a transformer?
The soft iron core concentrates the magnetic flux. It is laminated (split into thin, insulated sheets) to reduce energy losses due to eddy currents.
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In a Hall probe, what is the relationship between the measured Hall voltage ($V_H$) and the magnetic flux density (B)?
The Hall voltage is directly proportional to the magnetic flux density ($V_H \propto B$), assuming the current and probe dimensions are constant.
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What determines the polarity (which side is positive/negative) of the Hall voltage?
The polarity is determined by the direction of the current, the direction of the magnetic field (using Fleming's Left-Hand Rule on charge carriers), and the sign of the charge carriers (positive or negative).