Transcript ISNS3371_041707_bw

ISNS 3371 - Phenomena of Nature
The final will be Tuesday, April 24 at 8:00 AM. NOTICE THE TIME!
We will have two review sessions following the class on Thursday in the
lab at the far west end of Founders North. One from 11:00 - and the other
from 2:00 - ?. The test will cover any topic we have discussed in class and
will be approximately 40% comprehensive and 60% on what we have
covered since the last test. Topics include:
Fundamental quantities
Measurement units
Vectors, Scalars
Motion - distance, velocity, acceleration, projectiles
Force
Mass, momentum, impulse
Newton’s Laws of Motion
Law of Conservation of Momentum
Torque, angular momentum, conservation of angular
momentum
Matter - States of Matter
Energy, Work
Law of Conservation of Energy
Forms of Energy
ISNS 3371 - Phenomena of Nature
Transformation of energy
Power
Gravity - force, acceleration, weight, weightlessness
Heat, Temperature
Transfer of heat - Conduction, Convection
Change of state of matter
Gases - gas laws: Boyle, Charles, Guy Lusac, General
First Law of Thermodynamics
Archimedes’ Principle
Bernoulli Effect
Waves, Properties of Waves
Standing Waves
Sound Waves
Resonance, Interference
Pitch vs. Frequency,
Loudness vs. Intensity
Beats
Resonance in open and closed pipes
Harmonics
Doppler Effect
ISNS 3371 - Phenomena of Nature
Light as a wave, particle
Photoelectric effect
Electromagnetic Spectrum - Color
Light interaction with matter
Refraction, Reflection
Scattering - Blue Sky - Red Sunsets
Rainbows
Polarization
Lenses and mirrors
Telescopes
Spectroscopy - emission and absorption spectra
Thermal radiation/black body spectrum
Doppler effect - rotation, extrasolar planets
Electrical charge, voltage, current, power
Electrical circuits (parallel and series), resistance
Ohm’s law
AC and DC current
Magnetic fields, moving charges, right-hand rule
Induction, Faraday’s law
Motors and generators
Lenz’s law
ISNS 3371 - Phenomena of Nature
Voltage
Electric potential - change in electric potential is work done on charge by
an electric (Coulomb) force.
Remember: work = force X distance (over which force is applied)
Analogous to gravitational
potential energy: work done
by the force of gravity in
moving a mass through a
certain distance
Electric Potential
Voltage 
Ch arg e
Units of voltage are Volts (Joules/Coulomb). In a nine volt battery the
potential difference between the positive and negative terminals is precisely
nine volts. 
ISNS 3371 - Phenomena of Nature
Current
Establish a potential difference between two points and release some
charges - charges will be acted on by the electrical force and start to move
- this is a electric current - a flow of electrical charges. Just like the flow of
H2O is a water current.
 A current is the amount of charge that flows by a given point in a
certain time interval. Unit is Ampere (A = Coulombs/second)
In electrical circuits, consist of electrons in the wire moving from lower to
higher electrical potential.
By convention, electrical current flows from positive to negative - electrons
flow in opposite direction. In other words, a positive current flows from
higher to lower electrical potential.
ISNS 3371 - Phenomena of Nature
Resistivity and Circuits
If a wire is connected between two poles of a battery, a current flows.
This is a circuit. The electrons do not move completely freely - there is a
resistance to their flow - has to do with number of collisions electrons
make with other electrons and atoms. Amount of current dependent of
resistivity. Unit of electrical resistance is Ohm ().
Insulator - high resistivity
Conductor - low resitivity
Superconductor - zero resistivity
Dependent on material, temperature, length of wire
Electrical circuit like
hydraulic circuit with
flow of water
analagous to flow of
electrons.
ISNS 3371 - Phenomena of Nature
Power
Power is the rate of energy flow. Unit is Watt ( Watt = Joules/second)
Power = Voltage X Current - 1 W = 1 VA
Total amount of energy used = Watt X Time, This is how the power
company charges us for electricity - by the kilowatt hour (kWh)
The power rating of an appliance tells us the rate at which it uses electrical
energy. For example, a 1500 watt hair dryer uses 1500 joules of electrical
energy per second.
Keep a 60 watt light bulb on for a full day:
uses 60 watts x 24 hours = 1440 watt hours = 1.44 kilowatt hours
of energy. At 9 cents per kilowatt hour this would cost just under
15 cents.
kilowatt hour is a unit of energy - can convert it to joules:
1.44 kWh = 1440 J/s X 3600 s = 5,184,000 J
ISNS 3371 - Phenomena of Nature
Electrical Quantities
QUANTITY SYMBOL UNIT
MEANING
Charge
Q
Coulomb
(C)
A basic property of some
elementary particles. The electron
has a charge of -1.6 X 10-19 C
and the proton has a charge of
+1.6 X 10-19 C
Current
I
Ampere
(A)
(1 A = 1
C/sec)
Rate of flow of charge.
Potential
Difference
(voltage)
V
Volt (V)
(1 V = 1
J/C)
J= Joule
Potential energy difference per
coulomb of charge between two
points; corresponds to pressure in
water flow.
ISNS 3371 - Phenomena of Nature
QUANTITY SYMBOL UNIT
MEANING
Resistance
R
Ohm (Ω)
1Ω =
1 V/A
A measure of the opposition to the
flow of charge in a particular
circuit. For a given voltage, the
higher the resistance, the lower
the current.
Power
P
Watt (W)
(1 W =
1 VxA)
Rate of energy flow.
ISNS 3371 - Phenomena of Nature
Ohm’s Law
Ohm’s Law states that the amount of current in a circuit is proportional
to the voltage across the circuit and inversely proportional to the
resistance in that circuit
I=V/R
or
V = IR
Voltage = Current x Resistance
ISNS 3371 - Phenomena of Nature
Electrical Shock
“It’s not the voltage but the current.”
The current is what actually causes a shock - human body has
resistance of ~500,000  with dry skin - ~100  wet! Requires
conducting path.
Can cause: (1) burning of tissue by heating, (2) muscle contractions, (3)
disruption of cardiac rhythms.
Current (A)
Effect
0.001
Can be felt
0.005
Is painful
0.010
Causes spasms
0.015
Causes loss of muscle control
0.070
Goes through the heart - fatal after more than
1 second
ISNS 3371 - Phenomena of Nature
Circuits in Series
•Resistance (light bulbs) on same path
•Current has one pathway - same in every part of the circuit
•Total resistance is sum of individual resistances along path
•Current in circuit equal to voltage supplied divided by total resistance
•Sum of voltages across each lamp equal to total voltage
•One bulb burns out - circuit broken - other lamps will not light (think of
string of old Christmas lights)
ISNS 3371 - Phenomena of Nature
Water Analogy for Series Circuits
ISNS 3371 - Phenomena of Nature
Parallel Circuits
•Bulbs connected to same two points of electrical
circuit
•Voltage same across each bulb
•Total current divides among the parallel branches equals sum of current in each branch - current in each
branch inversely proportional to resistance of branch
•Overall resistance of circuit lowered with each
additional branch
•Household wiring (and new Christmas light strings)
designed in parallel - too many electrical devices on too much current - trip fuse/breaker
ISNS 3371 - Phenomena of Nature
Water Analogy for Parallel Circuits
ISNS 3371 - Phenomena of Nature
AC vs DC Current
Direct Current (DC) - electricity that you get from batteries - current
(movement of electrons) flows in one direction - from positive (high
potential) to negative (low potential) - note: electrons actually flow from
negative to positive.
Alternating Current (AC) - electricity that comes from the wall plug in your
home - current alternates in direction flowing first one way then the other
- electrons move back and forth in wire
ISNS 3371 - Phenomena of Nature
System of AC electricity in the US cycles the current from positive to
negative and back to positive 60 times a second - 60 Hz.
Standard household wiring design has two 120 volt "hot" wires and a
neutral which is at ground potential
- two 120 volt wires are obtained by grounding the centertap
of the transformer supplying the house so that when one hot
wire is swinging positive with respect to ground, the other is
swinging negative
- allows the use of either hot wire to supply the standard 120
volt household circuits.
Major advantage of AC over DC - AC voltages can be transformed to
higher or lower voltages.
- high voltages used to send electricity over great distances
from the power station can be reduced to a safer voltage for
use in the house
- higher voltage in transmission means less loss of power
ISNS 3371 - Phenomena of Nature
Magnetism
ISNS 3371 - Phenomena of Nature
The situation with forces due to magnetism is more complicated that
electrical/Coulomb forces.
-despite numerous searches, no evidence of
magnetic charges exist. In other words, there are
no particles which create a radial magnetic field
(usually termed monopoles by physicists) in the
way an electric charge creates a radial field.
Regions called
magnetic poles
produce magnetic
forces - a north
magnetic pole never
exists without a
south magnetic pole
- together called a
dipole
As for charges - like poles repel
and opposite poles attract.
Cutting a magnet in half will not isolate
a single north or south. One magnet
becomes two, then four, and so on.
ISNS 3371 - Phenomena of Nature
Magnetic fields can be created by moving electric charges, i.e. currents
produce fields.
Follows right-hand rule: point thumb
of right hand in direction of current magnetic field curls around wire in
direction of curled fingers
If the current flows in a
loop, the magnetic field
produced is like a bar
magnetic - curl fingers of
right hand in direction of
current flow - north pole
is in direction of thumb.
ISNS 3371 - Phenomena of Nature
The electron spins on its axis, giving rise to a
electron current in the direction of rotation.
The electron is like a magnetic dipole, a
miniature magnet, with a north end and a
south end.
In most substances, electrons spin in random directions - magnetic fields
cancel. For iron and other magnetic substances, the spin magnetism is
not canceled. Can be permanently magnetized by placing in strong
magnetic field and permanently aligning atoms - can be demagnetized by
dropping magnet and jostling atoms out of alignment.
Electromagnetic produced by wrapping coil
around iron bar - magnetic field produced
that aligns atoms in bar - more coils or
more current - larger magnetic field and
greater atomic alignment
ISNS 3371 - Phenomena of Nature
Induction
There is amazing reciprocity in nature - if moving electric charges create
magnetic fields, then magnetic fields must exert forces on moving electric
charges, just as electric charges create and are ``acted upon by''
magnetic fields. Force is perpendicular to magnetic field and direction of
motion.
Leads to the induction of current
in a wire moved through a
magnetic field - or a magnetic
field moved past a wire
Pass a magnet through a coil of
wire - produce a current
Faraday’s Law - The induced
voltage in a coil is proportional to
the number of loops multiplied by
the rate at which the magnetic
field changes within those loops.