Explain Electromagnetic Induction - Physics
Card 1 of 30
What experimental observation shows that reversing magnet polarity reverses induced current?
What experimental observation shows that reversing magnet polarity reverses induced current?
Tap to reveal answer
Galvanometer deflection reverses when the magnet is flipped. Flipping magnet reverses $\vec{B}$ direction and flux change sign.
Galvanometer deflection reverses when the magnet is flipped. Flipping magnet reverses $\vec{B}$ direction and flux change sign.
← Didn't Know|Knew It →
A loop moves out of a magnetic field region so flux decreases. What is the sign of $\frac{d\Phi}{dt}$?
A loop moves out of a magnetic field region so flux decreases. What is the sign of $\frac{d\Phi}{dt}$?
Tap to reveal answer
$\frac{d\Phi}{dt}<0$. Flux decreases as loop exits field region.
$\frac{d\Phi}{dt}<0$. Flux decreases as loop exits field region.
← Didn't Know|Knew It →
What experimental observation shows that faster motion induces a larger emf?
What experimental observation shows that faster motion induces a larger emf?
Tap to reveal answer
Greater galvanometer deflection at higher speed. Faster flux change produces larger $|\varepsilon|$ by Faraday's law.
Greater galvanometer deflection at higher speed. Faster flux change produces larger $|\varepsilon|$ by Faraday's law.
← Didn't Know|Knew It →
What evidence shows that induced current creates its own magnetic field?
What evidence shows that induced current creates its own magnetic field?
Tap to reveal answer
It produces a force opposing motion or a measurable magnetic effect. Induced currents create observable magnetic forces and fields.
It produces a force opposing motion or a measurable magnetic effect. Induced currents create observable magnetic forces and fields.
← Didn't Know|Knew It →
What does the minus sign in Faraday's law represent?
What does the minus sign in Faraday's law represent?
Tap to reveal answer
Lenz's law: induced emf opposes the change in magnetic flux. Induced current creates field opposing the flux change.
Lenz's law: induced emf opposes the change in magnetic flux. Induced current creates field opposing the flux change.
← Didn't Know|Knew It →
What is the induced current direction rule that opposes the change in flux called?
What is the induced current direction rule that opposes the change in flux called?
Tap to reveal answer
Lenz's law. States induced current opposes flux change.
Lenz's law. States induced current opposes flux change.
← Didn't Know|Knew It →
If a magnet is held stationary inside a coil, what is the induced emf?
If a magnet is held stationary inside a coil, what is the induced emf?
Tap to reveal answer
$\varepsilon=0$. No flux change means no induced emf by Faraday's law.
$\varepsilon=0$. No flux change means no induced emf by Faraday's law.
← Didn't Know|Knew It →
A magnet is moved toward a coil faster. How does induced emf magnitude change?
A magnet is moved toward a coil faster. How does induced emf magnitude change?
Tap to reveal answer
It increases because $\left|\frac{\Delta\Phi}{\Delta t}\right|$ increases. Faster motion gives larger flux change rate.
It increases because $\left|\frac{\Delta\Phi}{\Delta t}\right|$ increases. Faster motion gives larger flux change rate.
← Didn't Know|Knew It →
A coil is moved out of a uniform magnetic field region. What must be true for induction?
A coil is moved out of a uniform magnetic field region. What must be true for induction?
Tap to reveal answer
The flux through the coil must change. Leaving field changes flux from $BA$ to zero.
The flux through the coil must change. Leaving field changes flux from $BA$ to zero.
← Didn't Know|Knew It →
What happens to induced emf if the number of turns doubles, with the same $\frac{\Delta\Phi}{\Delta t}$?
What happens to induced emf if the number of turns doubles, with the same $\frac{\Delta\Phi}{\Delta t}$?
Tap to reveal answer
It doubles: $\varepsilon\propto N$. Faraday's law shows emf is directly proportional to $N$.
It doubles: $\varepsilon\propto N$. Faraday's law shows emf is directly proportional to $N$.
← Didn't Know|Knew It →
State the formula for motional emf for a rod of length $\ell$ moving at speed $v$ in field $B$.
State the formula for motional emf for a rod of length $\ell$ moving at speed $v$ in field $B$.
Tap to reveal answer
$\varepsilon=B\ell v$. Derived from Faraday's law for moving conductor.
$\varepsilon=B\ell v$. Derived from Faraday's law for moving conductor.
← Didn't Know|Knew It →
A rod moves parallel to magnetic field lines. What is the motional emf?
A rod moves parallel to magnetic field lines. What is the motional emf?
Tap to reveal answer
$\varepsilon=0$. No flux cut when motion is along field lines.
$\varepsilon=0$. No flux cut when motion is along field lines.
← Didn't Know|Knew It →
Which change increases magnetic flux $\Phi$ through a fixed coil: increasing $B$, $A$, or $\cos\theta$?
Which change increases magnetic flux $\Phi$ through a fixed coil: increasing $B$, $A$, or $\cos\theta$?
Tap to reveal answer
Any increase in $B$, $A$, or $\cos\theta$ increases $\Phi$. All three factors multiply to give flux.
Any increase in $B$, $A$, or $\cos\theta$ increases $\Phi$. All three factors multiply to give flux.
← Didn't Know|Knew It →
A coil rotates so $\theta$ increases from $0^\circ$ to $90^\circ$. What happens to $\Phi$?
A coil rotates so $\theta$ increases from $0^\circ$ to $90^\circ$. What happens to $\Phi$?
Tap to reveal answer
It decreases from $BA$ to $0$. $\cos(90°) = 0$, so flux becomes zero.
It decreases from $BA$ to $0$. $\cos(90°) = 0$, so flux becomes zero.
← Didn't Know|Knew It →
A north pole approaches a coil. Which face of the coil becomes a north pole?
A north pole approaches a coil. Which face of the coil becomes a north pole?
Tap to reveal answer
The near face becomes a north pole. Like poles repel to oppose approach.
The near face becomes a north pole. Like poles repel to oppose approach.
← Didn't Know|Knew It →
A north pole moves away from a coil. Which pole is induced on the near face of the coil?
A north pole moves away from a coil. Which pole is induced on the near face of the coil?
Tap to reveal answer
The near face becomes a south pole. Unlike poles attract to oppose separation.
The near face becomes a south pole. Unlike poles attract to oppose separation.
← Didn't Know|Knew It →
What evidence shows induced current depends on relative motion between magnet and coil?
What evidence shows induced current depends on relative motion between magnet and coil?
Tap to reveal answer
Moving the coil instead of the magnet gives the same deflection. Either motion produces same flux change.
Moving the coil instead of the magnet gives the same deflection. Either motion produces same flux change.
← Didn't Know|Knew It →
A transformer works by induction. What must be true about current in the primary coil?
A transformer works by induction. What must be true about current in the primary coil?
Tap to reveal answer
It must be changing (typically alternating). AC creates changing flux in the core.
It must be changing (typically alternating). AC creates changing flux in the core.
← Didn't Know|Knew It →
Use Faraday's law: if $\Delta\Phi=0.020,\text{Wb}$ in $0.10,\text{s}$ for $N=50$, find $|\varepsilon|$.
Use Faraday's law: if $\Delta\Phi=0.020,\text{Wb}$ in $0.10,\text{s}$ for $N=50$, find $|\varepsilon|$.
Tap to reveal answer
$|\varepsilon|=10,\text{V}$. $|\varepsilon| = 50 \times \frac{0.020}{0.10} = 10,\text{V}$
$|\varepsilon|=10,\text{V}$. $|\varepsilon| = 50 \times \frac{0.020}{0.10} = 10,\text{V}$
← Didn't Know|Knew It →
What condition must occur for an emf to be induced in a conductor or coil?
What condition must occur for an emf to be induced in a conductor or coil?
Tap to reveal answer
A changing magnetic flux linkage through it. Faraday's law requires flux change for induction.
A changing magnetic flux linkage through it. Faraday's law requires flux change for induction.
← Didn't Know|Knew It →
State Faraday's law in symbols for a coil with $N$ turns.
State Faraday's law in symbols for a coil with $N$ turns.
Tap to reveal answer
$\varepsilon=-N\frac{\Delta\Phi}{\Delta t}$. Induced emf equals turns times rate of flux change.
$\varepsilon=-N\frac{\Delta\Phi}{\Delta t}$. Induced emf equals turns times rate of flux change.
← Didn't Know|Knew It →
What does magnetic flux $\Phi$ equal for a uniform field through area $A$?
What does magnetic flux $\Phi$ equal for a uniform field through area $A$?
Tap to reveal answer
$\Phi=BA\cos\theta$. Flux is field times area times cosine of angle between them.
$\Phi=BA\cos\theta$. Flux is field times area times cosine of angle between them.
← Didn't Know|Knew It →
Identify the meaning of the minus sign in $\varepsilon=-N\frac{\Delta\Phi}{\Delta t}$.
Identify the meaning of the minus sign in $\varepsilon=-N\frac{\Delta\Phi}{\Delta t}$.
Tap to reveal answer
Lenz's law: induced emf opposes the flux change. Induced effects always oppose their cause.
Lenz's law: induced emf opposes the flux change. Induced effects always oppose their cause.
← Didn't Know|Knew It →
Which observation is direct evidence of electromagnetic induction in a coil?
Which observation is direct evidence of electromagnetic induction in a coil?
Tap to reveal answer
A galvanometer deflects only while flux is changing. No deflection when flux is constant proves change is needed.
A galvanometer deflects only while flux is changing. No deflection when flux is constant proves change is needed.
← Didn't Know|Knew It →
What happens to induced emf if the number of turns $N$ in a coil is doubled?
What happens to induced emf if the number of turns $N$ in a coil is doubled?
Tap to reveal answer
It doubles, since $\varepsilon\propto N$. Faraday's law shows emf is directly proportional to turn count.
It doubles, since $\varepsilon\propto N$. Faraday's law shows emf is directly proportional to turn count.
← Didn't Know|Knew It →
What is the direction rule for induced current when the magnetic flux increases?
What is the direction rule for induced current when the magnetic flux increases?
Tap to reveal answer
The induced field opposes the increase in flux. Lenz's law: induced current creates field opposing flux increase.
The induced field opposes the increase in flux. Lenz's law: induced current creates field opposing flux increase.
← Didn't Know|Knew It →
A loop has $A=0.50\ \text{m}^2$, $B=0.20\ \text{T}$, and $\theta=0^\circ$. What is $\Phi$?
A loop has $A=0.50\ \text{m}^2$, $B=0.20\ \text{T}$, and $\theta=0^\circ$. What is $\Phi$?
Tap to reveal answer
$0.10\ \text{Wb}$. $\Phi = BA\cos(0°) = 0.20 \times 0.50 \times 1 = 0.10\ \text{Wb}$.
$0.10\ \text{Wb}$. $\Phi = BA\cos(0°) = 0.20 \times 0.50 \times 1 = 0.10\ \text{Wb}$.
← Didn't Know|Knew It →
What is the direction rule for induced current when the magnetic flux decreases?
What is the direction rule for induced current when the magnetic flux decreases?
Tap to reveal answer
The induced field opposes the decrease in flux. Lenz's law: induced current tries to maintain original flux.
The induced field opposes the decrease in flux. Lenz's law: induced current tries to maintain original flux.
← Didn't Know|Knew It →
What experimental observation shows that reversing motion reverses induced current?
What experimental observation shows that reversing motion reverses induced current?
Tap to reveal answer
Galvanometer deflection reverses when motion direction reverses. Reversing $\frac{d\Phi}{dt}$ sign reverses induced current direction.
Galvanometer deflection reverses when motion direction reverses. Reversing $\frac{d\Phi}{dt}$ sign reverses induced current direction.
← Didn't Know|Knew It →
A loop has $A=0.30\ \text{m}^2$, $B=0.40\ \text{T}$, and $\theta=90^\circ$. What is $\Phi$?
A loop has $A=0.30\ \text{m}^2$, $B=0.40\ \text{T}$, and $\theta=90^\circ$. What is $\Phi$?
Tap to reveal answer
$0\ \text{Wb}$. $\cos(90°) = 0$, so flux is zero when $\vec{B} \perp$ area normal.
$0\ \text{Wb}$. $\cos(90°) = 0$, so flux is zero when $\vec{B} \perp$ area normal.
← Didn't Know|Knew It →