purpose of course introductory electromagnetism & optics o basic concepts in electromagnetism o...
TRANSCRIPT
Purpose of Course
Introductory Electromagnetism & Optics
o Basic concepts in electromagnetismo Linear Elements used in Circuitso Fundamentals of Opticso These topics are of importance in most branches of engineeringo Electronics and optics are integral parts of most systemso The physical principles underlying these are important to proper use
This course is not about electronics or optics as developed subjects, butrather the basic physics which underlies them.
Physics 102Piri Reis University 2011
Outcome of Course
At the end of the course students should have a basic knowledge of:
o Concepts in Electromagnetism, voltage, current, insulators,..o Linear Circuit Elements, resistors, capacitors, inductorso Kirchoff’s, Coulomb’s, Gauss’, Faraday’s, Ampere’s and Ohm’s lawso Refraction, reflection, and diffraction in Lighto 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 solvingStudents should:
o Attend the lectureso Solve the set problems.o Hand in homework when requested.
Lectures are more useful if you read aheado 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.
4 Capacitance Capacitors, Determination of Capacitance, Electric Energy Storage, Dielectrics
5 Electric Currents Batteries,Electric Current,Ohm’s Law,Power,Current Density and Drift Velocity.
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
8 Sources of Magnetic Field Magnetic Field Due to a Straight Wire, Ampère’s Law, Biot-Savart Law
9 Electromagnetic Induction Induced EMF,Faraday’s Law of Induction, EMF Induced in a Moving Conductor.
10 Electromagnetic Induction Inductance, Energy stored in a Magnetic Field, LR Circuits.
11 Electromagnetic Oscillations LC Circuits and Electromagnetic Oscillations, LRC Circuit
12 Light Reflection and Refraction, Snell’s Law, Fiber Optics
13 Diffraction and Polarization Diffraction by a Single Slit, Diffraction in the Double-Slit Experiment.
14 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
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
Lecture 1
BASICS Charge
o There are two kinds of electric chargeo Positiveo Negative
o What does this mean?o charge is a basic property of an object, just like
o positiono masso momentum
o It only really means something by defining what happenso 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, Co named after a famous French Scientisto The Coulomb is a large amount of chargeo The charge on one electron is 1.6 x 10-19 Coulombs
o Charge is everywhereo Everything is full of electric charge becauseo electrons and protons are chargedo 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 EXACTLYthe 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!
BASICS
SI system of units – this is the usual choice
hertz Hz frequency 1/s s-1
radian rad angle m·m-1 dimensionless
steradian sr solid angle m2·m-2 dimensionless
newton N force, weight kg·m/s2 kg·m·s−2
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 strengthV·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
lumen lm luminous flux lx·m2 cd·sr
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
katal kat catalytic activity mol/s s−1·mol
Name Unit symbol Quantity
metre m length
kilogram kg mass
second s time
ampere A electric current
kelvin K thermodynamic temperature
candela cd luminous intensity
mole mol amount of substance
Base units
Derived units (with a special name)
BASICS
o Properties of charge
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 linesemerging from the charge
More lines means moreeffects from the charge
Gathering lots of chargestogether 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 veryclean 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
Two balloons with charge on them
o Rubbing two materials together can move electrons
Must be the correct choices of material
Fur and rubber
Tyres and road (very dry)
o If electric charges can move freely in a material it is
A Conductor
o If electric charges stick in place on a material, it is
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 conductorAluminium 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
Ceramic is a good insulatorPVC tape is a goodinsulator
A person is not reallya conductor, but nota very good insulatoreither.
We give the electric field thesymbol E
E is a vector – direction matters
The electric field, E, has amagnitude and direction.
Looking in 2-D this is what it looks like
Arrows point away from +ve
and towards -veNo lines for neutral
The lines cannot cross, two positives behave like thisThe lines are forced apart
For a positive and a negativethe 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
the size of the forces between charges the formula for how it changes