7.9 - Electromagnetic Induction Flashcards
What is magnetic flux defined as?
The product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density
What is the equation to calculate magnetic flux?
Φ = BA
B = magnetic flux density
A = Cross sectional area
What are the units for magnetic flux?
Webers
Wb
What is flux linkage defined as?
The product of the magnetic flux and the number of turns of the coil.
What happens when an object experiences a change in a magnetic field?
It generates an electric field.
What is the equation to calculate magnetic flux linkage?
ΦN = BAN
Φ = magnetic flux (Wb)
N = number of turns of the coil
B = magnetic flux density (T)
A = cross-sectional area (m²)
What are the unit of magnetic flux linkage?
Weber turns.
What is the equation for flux linkage when the field lines are not completely perpendicular to the area A?
NΦ= BANcosθ
θ = angle between magnetic field lines and the line perpendicular to the plane of the area
When is magnetic flux at a maximum?
when cosθ = 1, hence θ=0 degrees (field lines perpendicular to the plane of the area)
When is magnetic flux at a minimum?
When cosθ = 0, hence θ = 90 degrees (field lines are parallel to the plane of the area).
When is an emf induced in a circuit?
When the magnetic flux linkage changes with respect to time. (e.g when a conductor moves through a magnetic field)
(so emf induced if there is a changing B,A or θ)
What is electromagnetic induction defined as?
The process in which emf is induced in a closed circuit due to changes in magnetic flux.
When a conductor cuts through the magnetic field lines what happens?
- This causes a change in magnetic flux
- which causes work to be done
- this work is transformed into electrical energy
- (therefore if attached to a circuit, a current is induced)
What is electromagnetic induction used in?
- Electrical generators which convert mechanical energy to electrical energy
- Transformers which are used in electrical power transmission
What factors increase the induced emf in the experiment which pushes a magnet in and out a coil?
- moving the magnet faster through the coil
- adding more turns to the coil
- increasing the strength of the bar magnet
What factors will increase the induced emf in the experiment which moves a wire through 2 magnets?
- increasing the length of the wire
- moving the wire between the magnets faster
- increasing the strength of the magnets
What is Faraday’s Law?
The magnitude of the induced emf is directly proportional to the rate of change in magnetic flux linkage.
What is Lenz’s law?
The induced emf acts in such a direction to produce effects that oppose the change causing it.
What is the equation to calculate the magnitude of the emf? (Faraday’s law)
ε = N Δɸ /Δt
ε = induced emf
N = number of turns of coil
Δɸ = change in magnetic flux
Δt = time intervals
What is the significance of the minus sign in Lenz’s law?
It shows the direction fo the induced emf. (the induced emf will oppose the change that caused it) - conservation of energy
How do you derive the equation ε = BLv?
movement of conductor through mag field =
s = vΔt
Area of mag flux that cuts through is:
A = LvΔt
total flux the conductor cuts through:
ΔΦ = BA = BLvΔt
ε = BLvΔt /Δt = BLv
what does the equation ε = BLv show?
The emf induced increases if:
- A longer conductor is in the field
- the magnetic field strength is larger
- the conductor cuts through the field lines faster
What is an alternator?
A generator of alternating current.
How do alternators work?
- they induce electrical current by rotating a coil in a magnetic field
- slip rings and brushes are connect the coil to an external circuit
- The output voltage and current change direction with every half rotation of the coil, producing alternating current (a.c).
When a coil rotates in a magnetic field, when is emf a maximum?
when θ = 90 degrees. The magnetic field lines are parallel to the plane of the area.
When a coil rotates in a magnetic field, when is emf a minimum?
when θ = 0 degrees. The magnetic field lines are perpendicular to the plane of the area.
(THIS IS THE OPPOSITE OF THE MAX AND MIN FLUX THROUGH THE COIL)
What is the equation for the induced emf in a rotating coil?
ε = BANω sin(ωt)
ε = emf induced in the coil (V)
B = magnetic flux density
A = cross-sectional area of the coil
ω = angular speed of the coil
t = time
