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Physics Chapter 12 : Topic 14
Faraday’s and Lenz’s Laws
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Faraday’s law states that an $\mathbf{e.m.f}$ is induced in a circuit when:
Reasoning: Faraday’s law states that a changing magnetic flux through a circuit induces an $\mathbf{e.m.f}$.
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In Faraday’s experiment, a galvanometer connected to a coil shows deflection when:
Reasoning: Movement of the magnet changes the magnetic flux linked with the coil, inducing an $\mathbf{e.m.f}$.
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If a bar magnet is held stationary inside a coil, the galvanometer shows:
Reasoning: A stationary magnet produces constant magnetic flux ; no change in flux means no induced $\mathbf{e.m.f}$.
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The main observation in Faraday’s electromagnetic induction experiment is:
Reasoning: Faraday demonstrated that changing magnetic flux induces $\mathbf{e.m.f.}$ and current.
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In the magnet-coil experiment, the magnitude of induced $\mathbf{e.m.f.}$ increases when:
Reasoning: Faster movement causes a greater rate of change of magnetic flux, producing larger $\mathbf{e.m.f}$.
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According to Faraday’s law, induced $\mathbf{e.m.f}$ is proportional to:
Reasoning: $\mathbf{E = -}$ $\frac{\mathbf{d(N\Phi)}}{\mathbf{dt}}$The induced $\mathbf{e.m.f.}$ depends on how quickly flux linkage changes.
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The negative sign in Faraday’s law represents:
Reasoning: The negative sign shows that induced $\mathbf{e.m.f}$ opposes the change causing it.
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Lenz’s law states that the induced current:
Reasoning: The induced current produces a magnetic effect that opposes the original change in flux.
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When the north pole of a magnet is pushed into a coil, the near face of the coil becomes:
Reasoning: The coil opposes the approaching North Pole by becoming a north pole, causing repulsion.
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When the north pole of a magnet is withdrawn from a coil, the near face of the coil becomes:
Reasoning: The coil tries to oppose the decrease in flux by attracting the departing north pole.
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Lenz’s law is a consequence of the law of conservation of:
Reasoning: If induced current supported the change, energy would be created without input, violating conservation of energy.
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In Faraday’s experiment, reversing the direction of magnet motion causes:
Reasoning: Reversing motion reverses the change in flux, so induced current direction changes.
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A magnet is moved toward a coil. The induced current produces a magnetic field that:
Reasoning: According to Lenz’s law, induced effects oppose the cause producing them.
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Which experiment demonstrates that changing magnetic flux induces $\mathbf{e.m.f}$?
Reasoning: Faraday used a coil and magnet to demonstrate electromagnetic induction.
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If a magnet is moved twice as fast through a coil, the induced $\mathbf{e.m.f}$ generally:
Reasoning: Faster movement increases the rate of change of magnetic flux.
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The induced $\mathbf{e.m.f}$ in a coil increases if:
Reasoning: More turns increase flux linkage change, producing greater induced $\mathbf{e.m.f}$.
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In an experiment, increasing the strength of the magnet causes induced $\mathbf{e.m.f}$ to:
Reasoning: A stronger magnet produces a larger change in magnetic flux.
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Which factor does NOT affect the magnitude of induced $\mathbf{e.m.f}$?
Reasoning: Wire colour has no effect on magnetic flux or induced $\mathbf{e.m.f}$.
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A coil is connected to a galvanometer. No deflection is observed when:
Reasoning: A stationary magnet produces no change in magnetic flux.
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Increasing the number of turns of a coil while keeping all other factors constant will:
Reasoning: Induced $\mathbf{e.m.f.}$ is proportional to the number of turns. $\Longrightarrow$ $\mathbf{E \propto N}$
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A magnet moving into a coil produces an induced current. If the magnet is stopped inside the coil:
Reasoning: Once motion stops, magnetic flux becomes constant and no $\mathbf{e.m.f.}$ is induced.
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If the magnetic flux through a coil changes more rapidly, the induced $\mathbf{e.m.f}$:
Reasoning: Faraday’s law states: $\mathbf{E \propto}$ $\frac{\mathbf{\Delta\Phi}}{\mathbf{\Delta t}}$
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The direction of induced current can be determined using:
Reasoning: Lenz’s law determines the direction of induced current.
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A coil and magnet experiment gives maximum galvanometer deflection when:
Reasoning: Faster motion produces greater flux change per unit time.
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When a magnet is pushed into a coil, mechanical work is required because:
Reasoning: Lenz’s law produces a force opposing the magnet’s motion, requiring external work.
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In electromagnetic induction, increasing the area of a coil generally:
Reasoning: Larger area allows more magnetic flux to pass through the coil.
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A stronger induced current is produced when:
Reasoning: Large induced $\mathbf{e.m.f}$ and low resistance produce larger current.
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If the magnetic flux through a coil increases, the induced current creates a magnetic field that:
Reasoning: Lenz’s law states the induced effect opposes the change in flux.
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Which combination produces the greatest induced $\mathbf{e.m.f}$?
Reasoning: High rate of flux change and more turns increase induced $\mathbf{e.m.f}$.
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Faraday’s and Lenz’s laws together explain:
Reasoning: Faraday explains the magnitude of induced $\mathbf{e.m.f}$, while Lenz explains its direction.
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In a generator, induced $\mathbf{e.m.f.}$ is produced because:
Reasoning: Rotation changes flux linkage with the coil, inducing $\mathbf{e.m.f}$.
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If the magnetic field strength around a coil is increased suddenly, the induced $\mathbf{e.m.f}$:
Reasoning: Any change in magnetic flux, including changing field strength, induces $\mathbf{e.m.f}$.
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The magnitude of induced $\mathbf{e.m.f}$ can be increased by:
Reasoning: More turns increase the change in flux linkage.
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A galvanometer connected to a coil detects induction by measuring:
Reasoning: The induced $\mathbf{e.m.f.}$ causes current that produces galvanometer deflection.
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If a magnet is moved out of a coil instead of into it, the induced current:
Reasoning: The change in flux is reversed, so the induced current direction reverses.
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