# Shared Flashcard Set

## Details

Ch 21 Electromagnetic Induction
concepts and formulas
32
Physics
03/24/2013

Term
 If an electric current can produce a magnetic field, can a magnetic field would induce an electric current ?
Definition
 yes, Almost 200 years ago, Faraday found evidence
Term
 Can a constant magnetic field produce current in a conductor?
Definition
 No, only a changing magnetic field can produce current.
Term
 what is an induced current?
Definition
 a current that is produced due to a changing magnetic field.   therefore we can say a changing magnetic field induces an emf (e.g. a battery).   this phenomenon is called electromagentic induction.
Term
 Faraday's experiments with a magnet &  a coil: What happens when the magnet moves up toward the coil: Is there a current produced? Is the magentic field increasing or decreasing in the coil?
Definition
 A current is induced. Magnetic field in the coil is increasing.
Term
 Faraday's experiments with a magnet &  a coil: What happens when the magnet moves down ,away, from the coil: Is there a current produced? Is the magentic field increasing or decreasing in the coil?
Definition
 A current is induced in the opposite direction.   The magnetic field in the coil decreases.
Term
 Faraday's experiments with a magnet &  a coil: What happens when the magnet is held steady and the coil is moved toward/away the magnet: Is there a current induced? Is the magentic field increasing or decreasing in the coil?
Definition
 Yes a current is still induced. It doesnt matter whether the coil or the magnet moves,  motion or change is required to induce an emf. So it is the realtive motion btwn the magnet & coil that is important.     the magnetic field in coil is constant.
Term
 the more rapidly the magnetic field changes the ____ (greater,lesser) the induced emf will  be in a loop of a wire
Definition
 greater
Term
 The induced emf in a wire loop is : inversely proportional/ proportional to the rate of change of magnetic flux through the loop.
Definition
 proportional
Term
 write the formula for:  magnetic flux for a uniform magnetic field through a loop of area(A) ΦB=
Definition
 ΦB= BAcosθ where: B is the component of the magnetic field perpendicular to loop θ: is the angle btwn B & a line perpendicular to the face  of the loop.
Term
 when the face of the loop is parallel to B, θ? ΦB (magnetic flux)?
Definition
 θ= 90 ΦB (magnetic flux) = 0 b/c cos 90=0
Term
 when the face of the loop is perpendicular to B, θ? ΦB (magnetic flux)?
Definition
 θ:0 ΦB (magnetic flux): BA (magentic field in Telsa's * area in m2)
Term
 Unit of magnetic flux is
Definition
 weber, Wb. 1 Wb = 1 T·m2
Term
 How is the magnetic flux is analogous to the electric flux?
Definition
 it is proportional to the total number of lines passing through the loop.
Term
 Faraday's law of induction says for 1 loop:  the induced emf E is proportional to ____and inversely proportional to
Definition
 proportional to: net change in magentic flux ΔΦB   inversely proportional to: change in time Δt
Term
 Faraday's law of induction says for N loops:  the induced emf E is proportional to ____ & inversely proportional to ______
Definition
 Note the emf in each loops are added together proportional to: net change in magentic flux ΔΦB   inversely proportional to: change in time Δt
Term
 what is Lenz's Law
Definition
 A current produced by an induced emf moves in a direction so that the magnetic field it produces tends to restore the changed field.
Term
 In  Lenz's Law what 2 magentic fields are we talking about?
Definition
 (1) the changing magnetic field or flux that induces the current   (2) the magnetic field produced by the induced current (note all currents produces an electric field)   the 2nd field opposses the 1st field.
Term
 Explain how a coil can produce its own magentic field
Definition
 the changing flux through the coil induces an emf through the coil =  a current is produced = this induced current produces its own magentic field
Term
 apply lenz's law to a coil & a magnet: if the distance btwn the coil & the magnet decreases (aka they got CLOSER) : 1.the magnet's magnetic field (aka the # of field lines through the coil) will increase/decrease?   2. causes the magnetic flux to increase or decrease?
Definition
 1. mag. field: increases 2.mag. flux: increases
Term
 apply lenz's law to a coil & a magnet: if the distance btwn the coil & the magnet increases (aka they get FURTHER APART) : 1.the magnet's magnetic field (aka the # of field lines through the coil) will increase/decrease?   2. causes the magnetic flux to increase or decrease?
Definition
 1. mag field: decreases 2. mag flux: decreases
Term
 Since magnetic flux: ΦB = BAcosθ an emf can be induced in what 3 ways?
Definition
 1. by changing the magnetic field 2. by the changing the area  (A) of loop inside the field 3. by changing the loop's orientation (the angle θ) with respect to the field.
Term
 Conceptual Question: In an induction  stove, an AC current passes around a coil that is a 'burner' (a burner that never gets hot). Why will it heat a metal pan but not a glass container?
Definition
 the AC current sets up a changing magentic    field that passes through the pan bottom   this changing magnectic field induces a current in the pan bottom   However a metal pan has little resistance = electrical energy is converted to thermal energy   a glass container has a high resistance= little current induced= little energy is transferred to container
Term
 true or false: an electric field will be induced at any in space where there is a changing magnetic field.
Definition
 true
Term
 if 2 coils of a wire are near each other, a changing current in one coil will induce an emf in the other.    is an example of _______ inductance?
Definition
 mutual inductance   For example: the change in the  emf induced in coil 2 is produced by the changing current in coil 1 (aka the rate of change of flux passing through it).
Term
 what is the units of mutual inductance (M)?
Definition
 V *s /A  = Ω *s = 1 Henry
Term
 mutual inductance (M) 1.what doesnt depend on? 2.what does it depend on?
Definition
 M is a" constant" does not depend on: current of coil 1 (I1)  (the coil who is doing the inducing to the other coil) depends on: geometric factors size shape # of turns realtive position of the 2 coils whether or not iron (or any ferromagnetic material is present).
Term
 mutual inductance: ↑ distance btwn coil 1 &2 means _____ lines of flux can pass through coil 2 M will be _____
Definition
 ↓ lines of flux can pass through coil 2 M will be ↓     (aka think the farther they are apart the less it can be induced)
Term
 when a changing current passes through a coil or a solenoid, a changing magnetic flux is produed inside the coil or a solenoid and this in turn produces an emf (e.g. a battery).This is called  _____ inductance
Definition
 self
Term
 In self- inductance, the induced emf ________ the change in flux
Definition
 opposses  (follows Lenz's law)
Term
 self- inductance: If the current through the coil is increasing, the increasing magnetic flux induces an emf that  ______
Definition
 opposes the current & tends to retard the increasing  the magnetic field.
Term
 self- inductance is proportional to
Definition
 the rate of change in current (and is in the direction opposed to the change).
Term
 self inductance ( the constant L) is units of ? depends on (3)?
Definition
 henry (Ω*s)   size,shape of coil  & prescense of an iron core.
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