Course notes with diagrams and worked solutions to examples problems.
Includes the Topics:
. Electric Charge, Fields & Gauss’ Law
• Electric Potential & Capacitance
• Magnetic Forces & Fields
• Electromagnetic Induction
• Magnetic Circuits
• AC circuit analysis & Complex Imp...
Week 2-1 Introduction to Electrical Machines
15 January 2023 15:40
Core Topics
Electric Charge, Fields & Gauss’ Law
• Electric Potential & Capacitance
• Magnetic Forces & Fields
• Electromagnetic Induction
• Magnetic Circuits
• AC circuit analysis & Complex Impedance
• Transformers
• DC Motors and Generators
Textbooks available on the VLE via course page: Principles of Physics, Fundamentals of Electric
Circuits
Around 30 hours of contact hours - need 70 self-study
Safety briefing during week 7 or 8 (IMPORTANT)
Simon.Bale@york.ac.uk
Office in Z block
Introduction to Electrical Machines Page 1
,Week 2-2 Electric Charge and Fields
16 January 2023 15:09
Electric charge:
Charge is a property of matter like mass
It causes matter to experience a force when placed in a electromagnetic field
Two types of charge, positive and negative
Charge written as Q; measured in coulombs
All charge is quantised, found in integer multiples of e = 1.6*10-19 (charge of an electron)
Can calculate the electrons in charge by dividing by 1.6*10-19
Charging an object:
Charge can be transferred between objects.
Objects can be charged by contact or by induction.
Which object loses or gains electrons is decided by a value which is the amount of energy it takes a
material to lose electrons.
In induction there is no contact. The rod causes the electrons to move away from it. Some electrons flow
to ground through the grounding wire. The object is now positively charged.
Total charge in an isolated system doesn’t change.
Conductors and Insulators:
Conductors have free electrons which allow the flow of current through the material.
Coulomb's Law:
F = K*((q1*q2)/r^2)r
K = 1/4piEo = 8.99*10^9 (nm^2/C^2)
R is in metres - cm and mm need to be converted
Remember to define what is the positive direction
F12 = Force on Q1 due to Q2
Use equation to find magnitude of each force.
Use trig to find the horizontal and vertical forces for Q2 as it's at an angle
Magnitude = 23N
Angle = 24
The Electric Field:
The positive charge experiences a force which is the vector sum of the forces
exerted by the charges on the object.
Test charge = q0
The electric field that exists at a point is the electrostatic force experienced by
a small positive test charge, q0, placed at that point divided by the charge
itself.
E = F/q0
Introduction to Electrical Machines Page 2
, The electric field that exists at a point is the electrostatic force experienced by
a small positive test charge, q0, placed at that point divided by the charge
itself.
E = F/q0
An electric field leads to a force, this can be calculated as follows.
Substitute numbers and equations into each other
Qo cancels
Solve
Electric Field Lines:
Electric field lines are lines of force that provide a map of the electric field in the space surrounding
electric charges
Electric field lines always point away from positive and towards negative charges
Dipoles - a positive and negative charge separated by a distance
E = kq(2d/z^3)
Introduction to Electrical Machines Page 3
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