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203 > Basics + Magnetism > Flashcards

Basics + Magnetism Flashcards

1
Q

explain why measuring the speed at the edge of the wheel is a poor way to represent its motion

A

depending on the distance to the COR the object it’s velocity changes .

Angular velocity is constant everywhere on a wheel - better way of representing motion

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2
Q

how to you represent the total angle (radians) that a wheel has turned in terms of :

Angular Velocity
Angular acceleration

A
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3
Q

How do you calculate angular velocity in terms of:

Radians
Frequency
RPM

A
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4
Q
A
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5
Q

What is Force

What is Torque

A

When a force is applied to an object, an acceleration is induced
F=Ma

Torque is produced when a force exerts a twisting moment on an object
T=Fr
(r= distance from force to axis of rotation - perpendicular distance)

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6
Q

What is Mechanical Work

How do you calculate Mechanical work

What is power

How do you calculate Power

A

Mechanical work is done when a force moves an object a distance

W=Fd or W = 2piTorque (d=2pir & F=T/R )

Power is the rate of which work is done

P= W/t or P = 2piT/t

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7
Q

A car has an engine power of 200kw and is moving at 20m/s, the rolling radius is 40cm. What is the torque produced by the engine

Assume 100% efficiency

A
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8
Q

explain how to calculate a gear ratio

A
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9
Q
A
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10
Q
A
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11
Q

describe the moment of interia

A

resistance to change in rotational motion

also called angular mass

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12
Q

Question

A

the torque calculated is the net torque

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13
Q

A Charged particle in a magnetic field will experience ______________________________________________________________________________

What’s this law Called

What’s the equation

A

a force perpendicular to both the direction of motion, and the direction to the magnetic field

Lorentz Force

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14
Q

Explain the Laplace Force

What’s the equation.

A

Current carrying wire in a magnetic field will experience a force perpendicular to the direction of current and magnetic field direction.

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15
Q

Explain the Biot-Savart Law
Whats the equation

A

If a current is passed through a wire, a magnetic field that loops around the wire will be produced.

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16
Q

What are the 4 rules associated with magnetic field plots

A
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17
Q

how do you calculate change in angular velocity in terms of torque.

write the general formula, and the one for a vehicle

A
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18
Q

what is ampere’s law

A
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19
Q

how do you calculate magnetic flux density?

what is the unit

A
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20
Q

find the expressions for
magnetic field intensity
magnetomotive force
flux density

for a transformer, specify the units

A
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21
Q

derive the equivalent of ohms law for for magnetic circuits

A
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22
Q

which one of the following materials is the best for a transformer core

A
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23
Q

draw a labelled hysteresis loop for the magnetisation of a transformer core

A
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24
Q

What is the Coercive Force

A

intensity of the magnetic field required to reduce the magnetic flix density of a magnetised material to zero after reaching saturation

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25
Q

What is remanence

A

the residual magnetic field density that remains when the magnetic field intensity drops to zero after it has reached saturation

26
Q

what is magnetic saturation

A

where magnetic flux density reaches a maximum for increasing values of magnetic field intensity H

27
Q

Evaluate the performance of a tranformers for the following two materials using their magnetisation curves

A

Hard materials are difficult to magnetise and remagnetise

Soft materials are easy to magnetise and remagnetise

A transformer core needs to magnetise and demagnetise rapidly
Hence a soft material would be better suited with a skinnier hysteresis , less hysteresis loss

28
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29
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30
Q
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31
Q

What is the difference between the Lorenz and Laplace force

A
32
Q
A
33
Q
A
34
Q
A

multiply force by 10 for the windings

35
Q
A
36
Q
A
37
Q

Answer part A

A
38
Q

answer part b

A
39
Q
A
40
Q
A
41
Q
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42
Q
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43
Q
A
44
Q

Draw the Circuit schematic for a sep ex DC motor

Derive the Equation for the :

steady state current through the armature

steady state torque produced

A
45
Q

For a Sep Ex DC Motor draw a graph of Torque against angular velocity , Assume the DC Motor is operating in a steady state at all times.

Demonstrate how the Graph changes when :

Voltage is Increased

Voltage is Decreased

Field Current is Increased

Field Current is Decreased

A
46
Q

Draw a graph of torque against angular velocity for a Sep Ex DC Motor, assume the dc motor is not operating in a steady state.

A
47
Q

Draw the Circuit schematic for a Shunt DC motor

Derive the Equation for the :

Steady state voltage through the armature and Field inductor

Angular velocity

A
48
Q

Draw a velocity agaisnt torque graph for a shunt DC Motor in ideal and real conditions

A
49
Q

Draw the Circuit schematic for a SeriesDC motor

Derive the Equation for the :

Steady state voltage

Torque Produced

A
50
Q

what’s the difference between a thyristor and a diode

A

Diode:

Allows one-way current flow.

Two terminals: anode and cathode.

Commonly used in rectification and protection.

Thyristor:

Acts as a switch controlling high voltage/current.

Three terminals: anode, cathode, gate.

Current pulse applied to gate, acts like a switch -unlike a transistor it the size of the base current doesn’t regulate the conductivity between the collector and emitter.

Used in power control and switching applications.

51
Q

draw a single diode phase rectifier, and single phase thyristor rectifier

draw the amplitude response produced by both

A
52
Q

What is faradays law

A

change in magnetic flux through a circuit induces an electromotive force (EMF) in the circuit, proportional to the rate of change of the magnetic flux.

53
Q

For a Sep Ex motor used as a generator, what is the equation for the induced voltage.

In terms of Change in Flux and Current

A
54
Q

What is the Efficiency of a DC Motor

A
55
Q

Compare a Brushed to a Brushless DC Motor

A

Brushed
Less Complex (More mature) technology

Cheaper

Easier Control

Higher Maintenance required on the brushes as they wear out over time

Brushes produce sparks -> fire hazard & signal interference

Lower Efficiency and Speed - More mechanical limits

Lower Power density

Brushless
More Complex (Modern) Technology

Expensive

Harder Control - microcontroller are required

Lower Maintenance required as there are no brushes

No sparking

Higher Efficiency and Speed - Less mechanical limits

Higher Power Density

56
Q

Draw a torque agaisnt speed graph for a series DC Motor in ideal conditions

A
57
Q
A
58
Q

how do you calculate power factor

A

apparent. /real power

59
Q

What are the applications for series, shunt and sep-ex dc motors

A
60
Q

what are the advantages and disadvantages of , shunt , series and sep ex dc motors

A
61
Q

How do you calculate the Peak induced Voltage in a rotation generated

A
62
Q

what are the main losses in dc motors

A

Electrical resistive losses within the armature

Hysteresis and Eddy Current losses induced in the magnetic core

Mechanical losses due to friction

Brush contact loss( brushed machines _> voltage drop at the interface)

Magnetic leakage currents (magnetic flux not contributing to torque)

203 (1 decks)

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