Download Lecture 1: Introduction to Electromagnetism

Welcome to electromagnetism
• Welcome to electromagnetism!
• I am Chris Blake and will be your lecturer for this
section of the Physics 2A course
• My contact details are [email protected], 9214
8624. You are welcome to contact me whenever
you like!
Lecture 1 : Welcome to Electromag
• Importance of electromagnetism
• Meaning of forces
• Synthesis of ideas
• Maxwell’s Equations
• Summary of the course
Importance of electromagnetism
• Electromagnetism is everywhere in our lives
Importance of electromagnetism
• Electromagnetism is one of the fundamental forces
that govern the physical Universe
Importance of electromagnetism
• How strong are electromagnetic forces?
𝑚1 𝑚2
𝐹𝑔 = 𝐺
𝑟2
𝑞1
𝑞2
𝑚1
𝑚2
𝐺 = 7 × 10−11 𝑁 𝑘𝑔−2 𝑚2
𝑞1 𝑞2
𝐹𝑒 = 𝑘𝑒 2
𝑟
𝑘𝑒 = 9 × 109 𝑁 𝐶 −2 𝑚2
• What is the ratio between the gravitational force 𝐹𝑔 and the
electrostatic force 𝐹𝑒 between two isolated electrons (mass
9 × 10−31 𝑘𝑔, charge 1.6 × 10−19 𝐶) ?
• Does your answer depend on the distance between the
electrons?
Importance of electromagnetism
• Electrostatic forces are reduced in practice because
matter is approximately electrically neutral
Importance of electromagnetism
• Electromagnetism is by far the strongest force in
our everyday experience
Importance of electromagnetism
• Electromagnetism is by far the strongest force in
our everyday experience
Importance of electromagnetism
• Other forces dominate on different scales …
Meaning of forces
• Coulomb’s Law tells us that like charges repel and
unlike charges attract. But what causes one charge
to feel the effect of the other?
• How is a force transmitted
across space?
• Is a force transmitted
instantaneously and, if so,
does that violate special
relativity?
Meaning of forces
• In our course, we consider that a force is
transmitted through the electromagnetic field
• An electric charge sets up an
electric field in the region of
space surrounding it
• Other charges, placed in an
electric field, will feel an
electrostatic force
Meaning of forces
• In our course, we consider that a force is
transmitted through the electromagnetic field
• An electric current (or
magnet) sets up a magnetic
field in the region of space
surrounding it
• Other currents (or magnets),
placed in a magnetic field,
will feel a magnetic force
Meaning of forces
• More advanced physics courses will continue to
refine this concept!
Synthesis of ideas
• Physics is about the synthesis of ideas :
understanding apparently different phenomena as
the joint consequences of a deeper reality
• For example, in 1666 Newton
realized that the same
gravitational force causes
both apples to fall downwards
from trees on the Earth, and
the Earth to orbit the Sun
Synthesis of ideas
• Electromagnetism represents another great
synthesis of ideas. Prior to 1830, electricity and
magnetism were considered separate phenomena
Electricity
Magnetism
Synthesis of ideas
• However, Faraday’s experiments demonstrated that
a magnet, as well as a battery, can drive a current
Electromagnetism
Synthesis of ideas
• Electricity and magnetism are therefore connected
by deeper principles, which we will discuss
Synthesis of ideas
• Charges produce electric fields, and currents
produce magnetic fields. But seen in a moving
reference frame, a charge becomes a current!
• Special relativity – which
describes how physics is
viewed in different
reference frames – must
allow us to transform
electrostatics into
magnetism
Synthesis of ideas
• The other great synthesis of ideas is that
electromagnetism can explain optics (light waves)
Synthesis of ideas
• In this course will see that light waves are just
vibrating electric and magnetic fields
Maxwell’s Equations
• Electromagnetism is governed by four simple and
elegant equations : Maxwell’s equations
• These equations are written
in the mathematical
language of vector calculus,
which we will develop
• In the following lectures we
will introduce these
equations, and the
phenomena they represent,
piece-by-piece
Summary of the course
• How an electric field is produced by charges (Lectures 2-5)
• How a magnetic field is produced by currents (Lectures 7-9)
• How these fields are modified in materials (Lectures 6, 11)
• Electromagnetic forces and their applications (Lecture 10)
• How a changing magnetic field produces an electric field, and
a changing electric field produces a magnetic field (Lectures
12-13)
• How these phenomena produce light (Lecture 14)
Summary of the course
• The electromagnetism course consists of …
• 3 lectures a week (Monday 8.30am in BA802,
Wednesday 10.30am in AGSE211, Thursday 2.30pm
in BA802)
• 1 tutorial a week (Thursday 12.30pm or 1.30pm)
• 2 labs (Wednesday 4.30pm, Weeks 8/10 or 9/11)
• 1 assignment (handed in Week 13)
• Half the Physics 2A examination!
Summary of the course
• I look forward to working with you!
• Just a reminder that my contact details are Chris
Blake, [email protected], 9214 8624