Electromagnetic Induction Flashcards
1
Q
Electro-Magnetic Equilibrium
A
- Direction of magnetic force FB pushing electrons down or up a wire will leave an excess of positive charge on the opposite end
- The separation of charge creates a uniform electric field E, within the wire pointing downward
- A charge q in the wire feels two forces: an electric force (FE= qE) and magnetic force (FB= qvB)
- If q is negative, FE is upward and FB is downward
- If q is positive, FE is downward and FB is upward
- In both cases, the forces act in opposite directions
- Once the magnitude of FE equals the magnitude of FB the charges in the wire are in electro-magnetic equilibrium
- Occurs when qE= qvB or (E= vb)
- The presence of the electric field creates a potential difference between the ends of the wire
- The potential difference Vba= Ellength (point b at upper end, point a lower end)
- As E= vB, Vba= vBllength
- The potential difference Vba= Ellength (point b at upper end, point a lower end)
- A charge q in the wire feels two forces: an electric force (FE= qE) and magnetic force (FB= qvB)
- The separation of charge creates a uniform electric field E, within the wire pointing downward
2
Q
Motional EMF
A
- Given a Rod sliding along a pair of conducting rails connected at the left by a stationary bar, the sliding rod completes a rectangular circuit, with the potential difference Vba causing current to flow
- The motion of the sliding rod through the magnetic field creates an electromotive force called motional emf:
- ℰ= vBllength
- Existence of a current in sliding rod causes the magnetic field to exert a force on it
- ℰ= vBllength
- The motion of the sliding rod through the magnetic field creates an electromotive force called motional emf:
3
Q
Power of External Agent on Rod
A
- Formula FB= IcurrentllengthB and the right-hand rule determine the direction of FB on the rod (existence of current in sliding rod causes magnetic field to exert force on it)
- An external agent must provide the same amount of force in the opposing direction to maintain the rod’s constant velocity and keep the current flowing
- Power that external agent must supply is P= Fv= IcurrentllengthBv
- The electrical power delivered to the circuit is P= IVba= Iℰ= IcurrentvBllength
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Two equations are identical
- The energy provided by the external agent is transformed first into electrical energy and then into thermal energy as the conductors making up the circuit dissipate heat
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Two equations are identical
- The electrical power delivered to the circuit is P= IVba= Iℰ= IcurrentvBllength
- Power that external agent must supply is P= Fv= IcurrentllengthBv
- An external agent must provide the same amount of force in the opposing direction to maintain the rod’s constant velocity and keep the current flowing
4
Q
Magnetic Flux
A
- The magnetic flux, ΦB, through an area A is equal to the product of A and the magnetic field perpendicular to it: ΦB= BperpA= BAcosθ
- Magnetic flux measures the densit of magnetic field lines that cross through an area
- The direction of A is taken to be perpendicular to the plane of the loop
- Magnetic flux measures the densit of magnetic field lines that cross through an area
5
Q
Faraday’s Law of Electromagnetic Induction
A
- The emf induced in a circuit is equal to the rate of change of the magnetic flux through the circuit
- ℰavg= -ΔΦB/Δt
- Induced emf can produce a current, which will make its own magnetic field
- Direction of induced current is determined by the polarity of the induced emf and is given by Lenz’s law: The induced current will always flow in the direction that opposes the change in magnetic flux that produced it
- Violation of Lenz’s law would lead directly to a violation of the law of conservation of energy
- Flux is scalar and has no direction, but referring to the “direction” of flux makes applying Lenz’s law easier
- What is actually referred to is the direction of the field producing the flux
- Direction of induced current is determined by the polarity of the induced emf and is given by Lenz’s law: The induced current will always flow in the direction that opposes the change in magnetic flux that produced it