Physics: Electricity & Magnetism
Electric field strength equation
E= F on q/q
Total energy to be converted to thermal energy can be written as
E=pt E= O^2Rt E= (v^2/r)t
Work=
F (force) D (direction
Coulomb's Law
F = k • Q1 • Q2 / d2
eddy current
Generated in the metal and produce a magnetic field that acts to oppose the motion that caused the currents
Volt
Measure of V. It is J/C
Are individual charges created?
No, Individual charges are never created or destroyed, they are just transferred
E=? (KWH)
PxT (KWxHours)
Coulomb (C)
The Si unit of charge
What happens to the current if the amount of charge increases?
The current increases as well
Electric current
The flow of charges
Resistance (R).
The measure of how strongly an object or a material impedes current produced by a potential difference.
electromagnetic induction
The process of generating a current through a circuit
Power
The work done in an amount of time
What three physical properties affect the resistance in a wire?
Thickness/thinness, Longer/shorter, or the type of material.
Ampere
Unit for current
equipotential.
When the electric potential difference between two or more positions is 0, the positions are called
What are the units for power?
Work (W)
A galvanometer indicates
a flow of electrons.
third right-hand rule
a method that can be used to determine the direction of the force on a current-carrying wire in a magnetic field
second right-hand rule
a method used to determine the direction of the field produced by an electromagnet, relative to the flow of conventional current
Gravitational forces
are always attractive.
Like kinds of magnetic poles repel while unlike kinds of magnetic poles
attract
Electrostatic forces
can be either repulsive or attractive,
Whereas electric charges can be isolated, magnetic poles
cannot
a battery
converts chemical energy to electrical energy
The resistance for most conductors __________ as the magnitude or direction of the potential difference applied to it changes.
does not vary
Any charge paces in an electric field experiences a force on it resulting from the ___________ at that location.
electric field
Over geologic history the Earth's magnetic field
has reversed direction many times.
Neutral atoms
have the same amount of positive and negative charges.
Electroscope
helps to determine charge. It is a metal knob connected by a metal stem to two thin, lightweight pieces of metal foil called leaves that are enclosed to eliminate air currents.
Positive charges flow from a ________ potential to a ________ potential
higher, lower
If the electric potential difference between the plates increases, the amount of charge on each place _______.
increases
Resistance ____________ as the cross sectional area decreases
increases
Resistance increases as length __________
increases
Magnetic domains normally occur in
iron
Electoral potential (voltage)
is electric potential energy per unit charge.
Like charges
like charges always repel
Coulomb's law only gives _________, not ___________.
magnitude, direction
Magnetism is due to the motion of electrons as they
move around the nucleus. spin on their axes.
The source of all magnetism is
moving electric charge.
if the charged rod is removed before the ground is broke, the sphere is ___________
neutral again
electrical resistance increases with...
-increasing wire length -increasing temperature -decreasing wire thickness
If a 9V battery exits at positive and connects at negative with a 7V battery, what is the final voltage?
16V
Electric circuit
A closed system or a path in which electrons from a voltage or current source flow
Capacitor
A small device for storing electric energy.
transformer
A transformer has two coils wound about the same core. An AC current through the primary coil induces an alternating EMF in the secondary coil. The voltages in alternating-current circuits may be increased or decreased by transformers.
What are the units for current?
Amps
What is ammeter?
An ammeter measures amps (current)
electrical resistance decreases with...
-decreasing wire length -decreasing temperature -increasing wire thickness
Larger the charge or distance moved...
...the greater the increase in the electric potential energy.
Elementary charge is equal to...
1.602 x 10^-19
A kilowatt-hour is equal to
1000 watts delivered continuously for an hour (3600 seconds). It is a unit of energy
To be able to find the voltage of two battery's, you must read what signs the battery's link together with. If a 6V battery exits at positive and connects at positive with a 3V battery, what is the final voltage?
3V
What is the resistance and range of a resistor with the colors, Yellow, Violet, Black, Gold?
47 ohms, and +- 2.35
One C is equal to...
6.24 x 10^18 electrons or protons.
the constant (K) in coulomb's law is equal to...
9.0 x 10^9
potentiometer
A device that can be used to change the current in a circuit in a continuous way
circuit schematic.
A diagram with symbols
Schematic
A drawing of a circuit using symbols
What is a voltmeter?
A voltmeter measures volts (voltage)
Series Circuit
An electric circuit in which electrical devices are connected along a single path. -the current that goes through each resistor is the same -the total resistance in the circuit is the sum of the resistances of each item in the circuit -the current in the circuit is given by Ohm's Law (voltage is supplied by battery, resistance is sum of each item) -voltage will drop across each device (total voltage drop will equal voyage supplied by battery)
equivalent resistance
the value of a single resistor that could replace all resistors in a circuit without changing the current
Parallel Circuit
An electric circuit in which electrical devices are connected along parallel paths -the voltage across each parallel path is the same -Ohm's Law applies to each branch -the total current is equal to the current through each individual path -the resistance decreases as the # of paths increases
electric circuit.
Any closed loop or conducting path allowing electric charges to flow
What is the color table?
Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Gray 8 White 9
Charging by induction
Charging a neutral object by bringing a charges object near
Charging by conduction
Charging a neutral object by touching that object with a charged object
Ohm's Law
Describes the relationship between current, resistance, and voltage: I=V/R amperes=volts/ohms
Types of Current
Direct Current (DC) , Alternating Current (AC)
One equation for energy
E= q change in V.
Solar winds headed in Earth's direction are deviated mainly by
Earth's magnetic field.
electrical pumps
Electrical pumps separate positive charges from negative charges (ex. battery or generator)
Direct Current (DC)
Electrically charged particles flowing in only one direction. (type of current set up in a simple current)
Alternating Current (AC)
Electrically charged particles the flow in alternating directions. (type of current in households)
Work on q=
FD
Field vectors
Field vectors Make a model of an electric field by using arrows to represent the field vectors at various locations Length of an arrow represents field strength in vectors.
ampere (A).
Flow of electric charge equal to one coulomb per second.
What colors are always at the bottom of the resistor? How do you find their range?
Gold and silver, gold multiply the resistance by 5% (0.05) for silver multiply the resistance by 10% (0.1) *don't forget all answers are + or -!!!!!*
(optional equation) P=? (Power)
I^2xR (Current squared multiplied by Resistance)
electric generator
Invented by Michael Faraday, converts mechanical energy to electrical energy. Consists of a number of wire loops placed in a strong magnetic field.
V=? (Voltage)
IxR (Current multiplied by resistance)
P=? (Power)
IxV (Current multiplied by Voltage)
Lenz's law
Lenz's law states that an induced current is always produced in a direction such that the magnetic field resulting from the induced current opposes the change in the magnetic field that is causing the induced current.
Newtons/Coulomb
Magnitude of the electric field is measured in this.
Battery
Maintains voltage by circuit, chemical --> electric
Anmeter
Measures current. It is connected in series with the part of the circuit it measures. (has very low internal resistances)
Voltmeter
Measures potential difference/voltage. It is connected in parallel with the circuit element that is measured. (has very high internal resistances)
electrical resistance
Measures the amount a material resists an electric current. Measured in Ohms (omega)
How do you convert 3 Watts to KW?
Move the decimal three to the left, .003 KW.
Electric field lines are directed towards _________
Negative charges.
What are the units for resistance?
Ohms (Ω)
Resistence
Opposition to the flow, slows down electrons
self-inductance
Self-inductance is a property of a wire carrying a changing current. The faster the current is changing, the greater the induced EMF that opposes that change.
Types of Circuits
Series Circuit, Parallel Circuit
Battery
Several galvanic cells connected together
Capacitance
Slope of the line in a net charge versus potential difference graph is a constant and called the _______ of a capacitor. You can measure the it in farads (F) where 1 F= I C/V.
mutual inductance
The changing field induces a varying EMF.
What happens to the current if the time increases?
The current will decrease
potential difference
The difference in electric potential between two points, measured in volts (V). (also known as voltage difference)
electric current
The flow of electric charge that transports energy from one place to another. In order for current to flow through a circuit, a voltage difference must be maintained. Measured in amperes (A).
Elementary charge
The magnitude of charge of a single electron or proton
Resistor
The object to the opposition of flow of electric charge
electromotive force (EMF)
The potential difference, or voltage, given to the charges by a battery
average power
The power produced by a generator is the product of the current and the voltage
Current can be changed by varying _________ or both.
V,R
How do power companies reduce the amount of energy lost to hear when transmitting electricity?
With low resistance and a high voltage
Do charges exert forces on each other?
Yes, separated positive and negative charges exert forces on one another
A plasma sphere's central electrode is...
a charged object whose net charge alternates rapidly between positive net charge and negative net charge.
parallel circuit
a circuit in which there are several different paths for a current
series circuit
a circuit in which there is only one current path
combination series-parallel circuit
a circuit that has some branches in parallel and some in series
ground-fault interrupter
a device that detects small differences in current caused by an extra current path and opens the circuit
galvanometer
a device that is used to measure very small currents can be used as a voltmeter or an ammeter
ammeter
a device used to measure the current in part of a circuit
voltmeter
a device used to measure the potential difference between two points
Charges exert forces on other charges at _________
a distance
electric current
a flow of charged particles
solenoid
a long coil of wire with many loops; fields from each loop add to the fields of the other loops, creating a greater total field strength
electromagnet
a magnet created when current flows through a wire coil
Surrounding every moving electron and stationary electron is
a magnetic field. an electric field.
Conductor
a material that allows charges to move easily (charge will spread out).
first right-hand rule
a method used to determine the direction of a magnetic field relative to the direction of conventional current
When current reverses direction in a wire, the surrounding magnetic field
also reverses direction.
electric motor
an apparatus that converts mechanical energy to electric energy and consists of a number of wire loops placed in a strong magnetic field
circuit breaker
an automatic switch that opens a circuit when the current reaches some set value, stopping electric charge flow
Surrounding every magnet is
an electric field. a magnetic field.
A current-carrying coil of wire is
an electromagnet.
When charges flow through the device that reduces electric potential energy, the energy is transformed into _____________
another kind of energy
An electric field exists when?
around any charged object. The field produces forces on other charged objects.
Electric potential difference increases as you pull a
as you pull a positive test charge away from a negative charge.
The direction of the force exerted on a moving charge in a magnetic field is
at right angles to the direction of the motion.
Positive atoms
atoms that are missing electrons
Negative atoms
atoms that have gained electrons
When a current-carrying wire is bent into a loop, its magnetic field inside the loop
becomes concentrated.
How do you produce a uniform electric field?
by placing two large flat conducting plates parallel to each other.
Van de graaff generators
can build up a large amount of net charge on its metal dome. When a person touches the metal dome, the positively charged dome attracts the electrons in the person's body. Their hair becomes positively charged and the individual hairs repel each other.
In the atoms of most materials the fields of individual electrons
cancel one another.
Electric potential difference in a uniform field equation
change in V= Ed
Magnetic field lines about a current-carrying wire
circle the wire in closed loops.
The number of electrons in a __________ does not change
closed circuit
Magnetic field strength about a magnet is strongest where magnetic field lines are
closer together
The field is stronger when the lines are _________
closer together
The force is stronger when the charges are __________
closer together
Generator
converts mechanical energy to electrical energy
a generator
converts mechanical energy to electrical energy
a solar cell
converts radiant energy to electrical energy
Potential energy ________ as you move the two charges further apart.
decreases
the electric potential _________ when a positive charge is moved towards a negative charge
decreases
polarized
describes the property of having two distinct, opposite ends, one of which is a north-seeking pole and the other of which is a south-seeking pole
a lamp
designed to convert electrical energy to radiant energy
only ________ in electric potential can be measured
differences
When an electron passes through the magnetic field of a horseshoe magnet, the electron's
direction is changed.
Ohm's law states that the current through a wire is _______________ to the potential difference between its ends.
directly proportional
JJ Thomson
discovered that all materials contain electrons
Ernest Rutherford
discovered that the atom has a massive positively charged nucleus surrounded by a cloud of orbiting electrons.
To weaken a bar magnet
drop it on a hard surface. put it in hot flames. whack it with a hammer.
If the connection to the ground is broken before the charged rod is removed, the sphere is ______________
either positively or negatively charged
A galvanometer can be calibrated to measure
electric current. electric voltage.
a motor
electric energy to mechanical energy
Which force field can increase a moving electron's speed?
electric field
Which force field can accelerate an electron?
electric field magnetic field
The work performed moving a charged particle in an electric field can result in the particle gaining _________ energy, __________ energy, or both.
electric potential, kinetic
Power is the rate at which
energy is transferred or transformed.
Compared to the huge force that attracts an iron tack to a strong magnet, the force that the tack exerts on the magnet is
equally huge.
Magnet A has twice the magnetic field strength of Magnet B and at a certain distance pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is
exactly 100 N.
The field is weaker when the lines are __________
farther apart.
fourth right-hand rule
find the force on the charges in the wire hold your right hand so that your thumb points in the direction in which the wire is moving and your fingers point in the direction of the magnetic field. The palm of your hand will point in the direction of the conventional (positive) current
Coulomb's law is only valid...
for point charges or for charges that are spread uniformly over a sphere.
An aurora borealis high above the atmosphere is due to
fountains of high-speed charged particles, trapping of charged particles by Earth's magnetic field, disturbances in Earth's magnetic field. (ALL OF THE ABOVE)
examples of insulators
glass, dry wood, plastics, cloth, and dry air
A compass is moved from the Northern Hemisphere to the Southern Hemisphere. Assume that the only magnetic field that acts on the compass is the Earth's magnetic field, and that this field is the same as the field of a dipole with the locations of the poles described in the textbook. When the compass is moved through the equator, the magnetic needle of the compass will change direction relative to the meridian
hardly at all.
If you break a bar magnet in half you'll
have two magnets
Place an iron rod inside a current-carrying coil of wire and you
increase the strength of the electromagnet.
The ___________ in potential difference by the generator equals the __________ in potential difference by the motor.
increase, decrease
Resistance usually increases as temperature ____________
increases
Total resistance ____________ with the length of wire
increases
Work _________ the electric potential energy of a two charge system.
increases
Higher capacitance is obtained by __________ the surface area and ____________ the separation of the plates.
increasing, decreasing
A resistor
is a device designed to have a specific resistance.
Insulator
is a material in which a charge will not move easily. (charge will stay in place)
electric field
is a property of the space around a charged object that exerts forces on other charged objects.
What does the electric potential difference depend on?
it does not depend on the magnitude of the test charge, it only depends on the field and the displacement.
The amount of energy used by a device is
its rate of energy consumption in joules per second, or watts, multiplied by the number of seconds the device is operated.
The purpose of increasing the potential difference when transmitting electrical energy over long distances is to decrease __________________.
joule heating loss
in the transmission of electrical energy, some power is lost to thermal energy. Electrical engineers call this unwanted thermal energy the _________
joule heating loss
Wood does not have magnetic properties because it contains no
magnetic domains.
Into which stable force field can a proton be placed at rest without being acted upon by a force?
magnetic field
The force that acts between a pair of magnetic poles depends on
magnetic pole strength. separation distance.
Pigeons navigate primarily by
magnetic sensors in their heads.
A current-carrying wire in a magnetic field
may be deflected. may experience a force.
An electron beam directed through a magnetic field
may experience a force. may be deflected.
A compass needle in a magnetic field
may experience a pair of torques.
examples of conductors
metals, plasma, graphite, air momentarily with lightning is involved.
Net charge can only be a _____ of e, not a _____ of e.
multiple, fraction.
Hard rubber and plastic have a tendency to become ________________
negatively charged
A superconductor is a material with ________ resistance
no
No net force acts on a loop of wire in a magnetic field when
no current is in the loop. no magnetic field lines pass through the loop.
A current-carrying loop of wire experiences no tendency to rotate in a magnetic field when
no field lines pass through the loop.
The flow continues until there is ______________ between the spheres
no potential difference
Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a
north pole.
The end of a compass needle that points to the south pole of a magnet is the
north pole.
The conventional direction of magnetic field lines outside a magnet are from
north to south.
A device having constant resistance independent of the potential difference ______________
obeys ohm's law
Resistance is measured in
ohms.
The energy carried by an electric current depends
on the charge transferred and the potential difference across which it moves.
primary coil
one coil
The flow of electrons and the direction of conventional current are in __________ directions
opposite
the potential increases in the direction _______ the electric field direction
opposite
secondary coil
other coil
Cosmic rays penetrate your body when
outdoors. in mountainous regions. safely in your home.
Always associate the words "voltage across" with a ____________ connection
parallel
Any time the current has two or more paths to follow in a circuit, the connection is a __________ connection
parallel
A beam of electrons can pass through a magnetic field without being deflected if the direction of the beam is
parallel to the field lines.
A beam of electrons passing through a magnetic field experiences maximum deflection if the direction of the beam is
perpendicular to the field lines.
The force a magnetic field exerts on a current-carrying wire is maximum when the wire is oriented
perpendicular to the magnetic field.
The force exerted on an electron moving in a magnetic field is maximum when the electron moves
perpendicular to the magnetic field.
A connection with one current path in a circuit is a __________ connection
series
Always associate the words "current through" with a _________ connection.
series
Refrigerator magnets are typically
short range
conventional current
the direction in which a positive test charge moves
electric field lines
the lines providing a picture of the size and strength of the field around a charged object.
An iron rod becomes magnetic when
the net spins of many of its electrons are aligned.
magnetic flux
the number of magnetic field lines that pass through a surface
short circuit
the occurrence when a circuit forms that has a very low resistance
Electric Power
the rate of energy transfer, or rate of work, or the amount of energy per unit of time: power= current x voltage (measured in watts (W))
The force on an electron moving in a magnetic field will be least when its direction is
the same as the magnetic field direction.
The current is ____ a series circuit.
the same everywhere
step-up transformer
the secondary voltage is larger than the primary voltage
The closer charges are to each other,
the stronger the electrostatic force between them.
Electrostatics
the study of electric charges/ the study of static electricity
step-down transformer
the voltage coming out of the transformer is smaller than the voltage put in
armature
the wire could of an electric motor, made up of many loops mounted on an axle of shaft; torque on an armature, an the motor's resultant speed, is controlled by varying the current through the motor
Application of Electrostatic Forces:
there are many commercial and industrial applications of electrostatic forces. Tiny paint droplets are charged by induction. Photo copies. Laser printers.
The total charge passing through a point on a circuit is the current multiplied by the _______ the charge flows
time
Force is directly proportional...
to the strength of the test charge.
Unlike charges
unlike charges always attract
(optional equation) P=? (Power)
v^2/R (Voltage squared divided by resistance)
Electrostatic force is a _________, it has magnitude and direction.
vector
Power is measured in
watts (W).
Force varies directly
with the charge on the body.
Magnitude of electric force varies inversely
with the square of the distances between the center of the spheres.
How do you determine direction of electrostatic force?
you can determine direction by drawing a diagram of force vectors and applying vector addition.
Electric potential difference (V)=
ΔV=work on q/q. (the work done moving a positive test charge between two points in an electric field divided by the magnitude of the test charge).
I=? (Current)
Q/T (Charge divided by Time)
Equation for Resistance.
R= V/I (potential difference divided by current)
What is the purpose of a generator?
Creates electrical energy, and converts mechanical energy into electrical energy
Which way does conventional current flow?
Positive ---> negative
What are the two different types of charges
Positive and negative
Three Equations for Power.
Power is equal to the current times the potential difference. (P=IV) Power is equal to = i^2R Power is also equal to= V^2/R
Which is greater, the speed of an electron traveling through a wire, or the speed of light?
The speed of light
voltage divider
a series circuit used to produce a voltage source from a higher-voltage battery
fuse
a short piece of metal that melts if a current that is too large passes through it
domain
a very small group, usually 10-1000 u, that is formed when the magnetic fields of the electrons in a group of neighboring atoms are aligned in the same direction
The magnetic fields of a pair of nearby magnets can
add or subtract by vector rules.
Magnetic fields are produced by
all moving electrical charges.
An ammeter measures
current
The intensity of cosmic rays bombarding the Earth's surface is most at the
poles
glass and wool have a tendency to become ____________.
positively charged
The EPD is higher near the ________ charged plate and lower in the ________ charged plate.
positively, negatively
There is no _____________ across a superconducting wire
potential difference
A voltmeter measures
potential differences
If a magnet produces a force on a current-carrying wire, the wire
produces a force on the magnet.
Earth's magnetic field is
protective to life on Earth.
C=
q/ change in V.
Grounding
removing excess charge by connecting an object to earth.
When you pull a + charge from a + charge, there is a _____________ force between the two.
repulsive
Although a magnet can change the direction of travel of an electron beam, it cannot change its
speed kinetic energy.
Electric potential difference does not depend on the path used to go from one position to another. It depends only on the _________ positions on that path.
starting and final
Electrostatic forces are typically ________ than gravitational forces.
stronger
In an electric circuit, the potential difference provided by the generator or other energy source, Vsource, is equal to the ____ of drops in electric potential across the resistors.
sum
A superconducting magnet uses
superconducting coils.
magnetic fields
the area around a magnet, or around any current-carrying wire or coil of wire, where a magnetic force exists