Transcript Slide 1

Physics 102
Piri Reis University 2011
Purpose of Course
Introductory Electromagnetism & Optics
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Basic concepts in electromagnetism
Linear Elements used in Circuits
Fundamentals of Optics
These topics are of importance in most branches of engineering
Electronics and optics are integral parts of most systems
The physical principles underlying these are important to proper use
This course is not about electronics or optics as developed subjects, but
rather the basic physics which underlies them.
Outcome of Course
At the end of the course students should have a basic knowledge of:
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Concepts in Electromagnetism, voltage, current, insulators,..
Linear Circuit Elements, resistors, capacitors, inductors
Kirchoff’s, Coulomb’s, Gauss’, Faraday’s, Ampere’s and Ohm’s laws
Refraction, reflection, and diffraction in Light
Optical elements, lens, fibre optics, prism
Structure of Course
There are 14 weeks, each with 3 hours of theory and 2 hours
dedicated to laboratory exercises and problem solving
Students should:
o Attend the lectures
o Solve the set problems.
o Hand in homework when requested.
Lectures are more useful if you read ahead
o Lecture content by week is outlined [approximate]
o Read about subject before lecture [see reference list]
o Ask questions in class
Structure of Course
Structure of Course
1
Electric Field
Electric Charge, Static Electricity, Insulators, Conductors, Electric Field.
2
Gauss’s Law
Electric Flux, Coulomb’s Law, Gauss’s Law, and Applications of Gauss’s law.
3
Electric Potential
Electric Potential Energy, Potential Difference,Potential Due to Any Charge Dist.
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Capacitance
Capacitors, Determination of Capacitance, Electric Energy Storage, Dielectrics
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Electric Currents
6
DC Circuits
EMF, Resistors in Series and in Parallel, Kirchhoff’s Rules, RC Circuits.
7
Magnetism
Magnets, Magnetic Fields, Force on an Electric Current in a Magnetic Field
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Sources of Magnetic Field
Magnetic Field Due to a Straight Wire, Ampère’s Law, Biot-Savart Law
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Electromagnetic Induction
Induced EMF,Faraday’s Law of Induction, EMF Induced in a Moving Conductor.
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Electromagnetic Induction
Inductance, Energy stored in a Magnetic Field, LR Circuits.
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Electromagnetic Oscillations LC Circuits and Electromagnetic Oscillations, LRC Circuit
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Light
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Diffraction and Polarization Diffraction by a Single Slit, Diffraction in the Double-Slit Experiment.
14
Batteries,Electric Current,Ohm’s Law,Power,Current Density and Drift Velocity.
Reflection and Refraction, Snell’s Law, Fiber Optics
Review
Structure of Course
Examinations
o There will be two mid-term exams and
o One final examination.
o The examinations will be at the same level as the homework
problems
Lecture 1
o Aim of the lecture
 Reminder of Basics:
 static charge
 units
 insulators, conductors
 electric field
o Main learning outcomes
 familiarity with
 static electricity
 induced charge
 monopole and dipole electric fields
 materials which insulate and conduct
BASICS
Charge
o There are two kinds of electric charge
o Positive
o Negative
o What does this mean?
o charge is a basic property of an object, just like
o position
o mass
o momentum
o It only really means something by defining what happens
o It cannot really be ‘explained’ in terms of anything else
o When drawing diagrams of objects with charge
 usually positive is RED
 negative BLUE (or black)
 but many other colours used, so be careful!
 Every object is one of:
 positive
 negative
 neutral (no charge)
BASICS
Units of charge
o Coulombs, C
o named after a famous French Scientist
o The Coulomb is a large amount of charge
o The charge on one electron is 1.6 x 10-19 Coulombs
o Charge is everywhere
o Everything is full of electric charge because
o electrons and protons are charged
o atoms are made from electrons and protons (and neutrons)
o 1 glass of water has
 approximately 3.6 x 1026 electrons in it
 and 4 x 1026 protons
o BUT
 the effects of positive electric charge are cancelled by the effects of negative
 most objects (certainly all ordinary matter) have the same quantity of each kind
 which means they end up being neutral overall
o An atom,
 core of protons and neutrons
 ‘shells’ of electrons outside
 positive ‘nucleus’
 negative electron shells
 total charge is zero
 atoms are neutral
o All matter is made from atoms
 atoms combine into molecules
 molecules can bind in chains
o All this works because of charge
The charge on the electron is EXACTLY
the opposite of the charge on the proton
this is a mystery – scientists try to understand why
but if it wasn’t the case then we could not exist!
Name
BASICS
m
length
kilogram
kg
mass
second
s
time
ampere
A
electric current
kelvin
K
thermodynamic temperature
candela
cd
luminous intensity
mol
amount of substance
mole
hertz
Hz
frequency
1/s
s-1
radian
rad
angle
m·m-1
dimensionless
steradian
sr
solid angle
m2·m-2
dimensionless
kg·m·s−2
newton
N
force, weight
kg·m/s2
pascal
Pa
pressure, stress
N/m2
m−1·kg·s−2
joule
J
energy, work, heat
N·m = C·V = W·s
m2·kg·s−2
watt
W
power, radiant flux
J/s = V·A
m2·kg·s−3
coulomb
C
electric charge
s·A
s·A
volt
V
voltage
W/A = J/C
m2·kg·s−3·A−1
farad
F
electric capacitance
C/V
m−2·kg−1·s4·A2
ohm
Ω
electric resistance
V/A
m2·kg·s−3·A−2
siemens
S
electrical conductance
1/Ω
m−2·kg−1·s3·A2
weber
Wb
magnetic flux
J/A
m2·kg·s−2·A−1
tesla
T
magnetic field strength
V·s/m2 = Wb/m2 = N/(A·m
)
kg·s−2·A−1
henry
H
inductance
V·s/A = Wb/A
m2·kg·s−2·A−2
Celsius
°C
temperature
K − 273.15
K − 273.15
cd·sr
lumen
lm
luminous flux
lux
lx
illuminance
lm/m2
m−2·cd·sr
becquerel
Bq
radioactivity
1/s
s−1
gray
Gy
absorbed dose
J/kg
m2·s−2
sievert
Sv
equivalent dose
J/kg
m2·s−2
−1
Quantity
metre
SI system of units – this is the usual choice
lx·m2
Unit symbol
Base units
Derived units
(with a special name)
BASICS
o Properties of charge
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Like charges repel
Opposite charges attract
neutral objects are not attracted or repelled
o Charge is conserved
 the total charge in a closed system cannot change
 but this means only that
 (quantity of positives) – (quantity of negative) = constant
=
+
The effects of charge are described using a ‘field’
Think of as field lines
emerging from the charge
More lines means more
effects from the charge
Gathering lots of charges
together is what is called
‘static electricity’
o Each strand of the girl’s hair has
been given lots of negative charge
o Hairs repel each other
The hair needs to be very
clean for this to work well, so
It does not work as well for boys!
o Static Electricity is formed when
 electrons are removed from atoms
 collected together in a different place
o Rubbing two materials together
can move electrons
 Must be the correct choices of
material
 Fur and rubber
 Tyres and road (very dry)
Two balloons with charge on them
o If electric charges can move freely in a material it is
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A Conductor
o If electric charges stick in place on a material, it is
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An Insulator
o [there are also materials in between called ‘semi-conductors’]
o To keep the charge on her hair, the girl is standing
on an insulator.
o If she stood on the ground her hair would droop
(the ground is not a very good conductor, but enough)
o Conductors
 have ‘loose’ electric charges that can move
 metals have loose electrons
 ionic liquids have free atomic ions
 most conductors in use are metallic
Copper is a good conductor
Aluminium is often used
Gold is very good, but a bit expensive
o Insulators
 have no ‘loose’ electric charges
 many materials are insulators
 but many are not very good ones, they
 will conduct a little
PVC tape is a good
insulator
A person is not really
a conductor, but not
a very good insulator
either.
Ceramic is a good insulator
We give the electric field the
symbol E
E is a vector – direction matters
The electric field, E, has a
magnitude and direction.
Looking in 2-D this is what it looks like
and towards -ve
Arrows point away from +ve
No lines for neutral
The lines cannot cross, two positives behave like this
The lines are forced apart
In 2-D
For a positive and a negative
the field lines do this in 2-D
This is called a ‘dipole’
Very complicated patterns of field lines can exist
Induced Charge
If a positive charge is brought close to a metal bar
• Then some electrons in the bar move towards the charge
• Which leaves fewer at the other end of the metal
• But the atoms cant move, so
• There is a net positive charge left at the other end of the metal
• These charges caused by movement are called ‘induced charges’
In another lecture we will consider
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the size of the forces between charges
the formula for how it changes