Electromagnetism Flashcards

1
Q

How to determine the magnetic field pattern of a length of wire?

A

Right hand thumb rule
Thumb = Direction of conventional current
Fingers = Direction of magnetic field

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2
Q

How to determine magnetic field of a solenoid?

A

Right hand thumb rule
Thumb=Direction of magnetic field
Fingers=Direction of current

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3
Q

What fingers represent what in Fleming’s left-hand thumb rule?

A

Thumb = Force (N)
Index Finger = Magnetic field,N–>S
Middle Finger = Current (A)

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4
Q

What’s the equation for a force on a current carrying wire?

A

F=BILsinθ
F=Force (N)
B=Magnetic flux density (T)
I=Current(A)
L=Length of wire in magnetic field(m)

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5
Q

If a wire is perpendicular in a uniform magnetic field, what is the force on the wire?

A

F=BIL
(Since sin90 = 1)

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6
Q

Define the Tesla

A

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

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7
Q

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:

A

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

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8
Q

State Faraday’s Law:

A

The magnitude of an induced emf in a wire loop is equal to the rate of change of magnetic flux linkage

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9
Q

Define magnetic flux

A

ø=BA
Magnetic flux = Magnetic flux density x cross-sectional area

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10
Q

What’s magnetic flux measured in?

A

Weber’s
1 Weber = 1 Tesla metres squared

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11
Q

What’s the equation for magnetic flux when there’s an angle?

A

ø=BAcosθ

When the angle is 90, the magnetic flux is zero

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12
Q

What’s the equation for magnetic flux linkage?

A

øN=BANcosθ

Magnetic flux linkage = Magnetic flux x Number of turns in a coil

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13
Q

State Lenz’s Law

A

An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original change in magnetic flux.

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14
Q

Write down the equation for Faraday’s law:

A

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

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15
Q

If there’s a graph of emf plotted against t what does the area underneath the line represent?

A

The change in magnetic flux linkage = -E▲t

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16
Q

Transformer equation involving voltage and number of turns on coils:

A

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

17
Q

Write down an equation that links the conservation of energy to a transformer if the transformer is 100% efficient:

A

Since P=IV
I_pV_p=I_sV_s

18
Q

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:

A

F_E=F_B
EQ=BQv
E=Bv

v=E/B
(where v = velocity, E= electric field strength and B = magnetic flux density)