Electromagnetism Flashcards
How to determine the magnetic field pattern of a length of wire?
Right hand thumb rule
Thumb = Direction of conventional current
Fingers = Direction of magnetic field
How to determine magnetic field of a solenoid?
Right hand thumb rule
Thumb=Direction of magnetic field
Fingers=Direction of current
What fingers represent what in Fleming’s left-hand thumb rule?
Thumb = Force (N)
Index Finger = Magnetic field,N–>S
Middle Finger = Current (A)
What’s the equation for a force on a current carrying wire?
F=BILsinθ
F=Force (N)
B=Magnetic flux density (T)
I=Current(A)
L=Length of wire in magnetic field(m)
If a wire is perpendicular in a uniform magnetic field, what is the force on the wire?
F=BIL
(Since sin90 = 1)
Define the Tesla
1 Tesla is the magnetic flux density that causes a force of 1N on a wire carrying current of 1A of length 1m, which is at right angles to the magnetic field
Find the equation for a force on a charged particle due to a magnetic field:
Then find the radius of circular motion of the particle:
F=BIL
Since I=Q/t
F=BLQ/t
Since v=L/t
Therefore F=BQv
Since the charged particle is executing circular motion we can state : mv^2/r=BQv
Therefore
r=mv/BQ
State Faraday’s Law:
The magnitude of an induced emf in a wire loop is equal to the rate of change of magnetic flux linkage
Define magnetic flux
ø=BA
Magnetic flux = Magnetic flux density x cross-sectional area
What’s magnetic flux measured in?
Weber’s
1 Weber = 1 Tesla metres squared
What’s the equation for magnetic flux when there’s an angle?
ø=BAcosθ
When the angle is 90, the magnetic flux is zero
What’s the equation for magnetic flux linkage?
øN=BANcosθ
Magnetic flux linkage = Magnetic flux x Number of turns in a coil
State Lenz’s Law
An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original change in magnetic flux.
Write down the equation for Faraday’s law:
E = -▲BAN/▲t
E = emf
B=Magnetic flux density
A= Current
N = Number of turns in a coil
t = time
▲BAN is also the change in magnetic flux linkage
If there’s a graph of emf plotted against t what does the area underneath the line represent?
The change in magnetic flux linkage = -E▲t
Transformer equation involving voltage and number of turns on coils:
V_p/V_s = N_p/N_s
V_p= Applied voltage to primary coil (V)
V_s = Output voltage of secondary coil (V)
N_p=Number of turns on primary coil
N_s= Number of turns on secondary coil
Write down an equation that links the conservation of energy to a transformer if the transformer is 100% efficient:
Since P=IV
I_pV_p=I_sV_s
A charged particle is placed in an electric and magnetic field. A charged particle in an electric field experiences a force F_E=EQ. The same charged particle will experience a force from the magnetic field F_B=BQv. If the two fields are in such a direction that the forces act in equal and opposite directions on the charged particle (meaning the charged particle will move in a straight line with constant speed), then find an equation for the velocity of the particle:
F_E=F_B
EQ=BQv
E=Bv
v=E/B
(where v = velocity, E= electric field strength and B = magnetic flux density)