9702 · 20.2
Force on a current-carrying conductor flashcards
Revision flashcards for Cambridge 9702 Force on a current-carrying conductor (syllabus 20.2). Flip, recall, then mark a real past-paper question.
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What is the SI unit for magnetic flux density?
Tesla (T)
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State the formula for the force on a current-carrying conductor in a magnetic field, including the angle.
F = BILsinθ
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Which rule determines the direction of force on a current-carrying conductor in a magnetic field?
Fleming's Left-Hand Rule
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When does a current-carrying conductor experience maximum force in a magnetic field?
When the current direction is perpendicular (90°) to the magnetic field lines.
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What is the formula for the velocity of particles that pass undeflected through a velocity selector?
v = E/B
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Define magnetic flux density (B).
Force per unit current per unit length on a straight wire placed perpendicular to the magnetic field.
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What is the 'motor effect'?
The phenomenon where a current-carrying conductor experiences a force when placed in an external magnetic field.
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When does a current-carrying conductor experience *no* force in a magnetic field?
When the current direction is parallel (0° or 180°) to the magnetic field lines.
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How is Fleming's Left-Hand Rule adapted for a moving positive charged particle?
The particle's direction of motion (velocity) replaces the current direction (middle finger).
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What is the purpose of a velocity selector?
To allow only charged particles with a specific velocity to pass through undeflected, by balancing electric and magnetic forces.
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What is the path of a charged particle that enters a uniform magnetic field at a right angle to the field lines?
A circular path. The magnetic force provides the necessary centripetal force.
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How do you find the direction of force on a *negative* charge (like an electron) using Fleming's Left-Hand Rule?
Point the middle finger (Current) in the direction *opposite* to the electron's velocity. The thumb will then show the direction of the force.
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What is the formula for the radius of the circular path of a charged particle in a magnetic field?
r = mv / BQ, where m is mass, v is velocity, B is magnetic flux density, and Q is charge.
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Under what condition does a charged particle move in a helical (spiral) path in a magnetic field?
When its velocity has components both parallel and perpendicular to the magnetic field. The parallel component is unaffected, and the perpendicular component causes circular motion.