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AP Physics B – Ody“NOTES”ki
ELECTRICITY & MAGNETISM
ELECTRODYNAMICS
1) Static Electricity
a) The study of stationary electrons
b) Electrons are the only particles that are able to move
2) Particles
PARTICLE
CHARGE
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MASS
Proton
+1.6 × 10
C
1.67 × 10-27 kg
Electron
-1.6 × 10-19 C
9.11 × 10-31 kg
Neutron
0
1.67 × 10-27 kg
3) Conservation of Charge – The net charge of an isolated system remains constant
a) The charge of an electron or proton’s charge is the lowest natural charge found in nature
b) The charge is quantized; No fractions of charges is possible
c)
i)
ii)
d) Conductor – A material that allows the easy flow of electrons; typically metals
e) Insulator – A material that does not allow the easy flow of electrons; typically non-metals
f) Semiconductors – A material that has both Conductor and Insulator properties; Silicon in computer chips
g) Conduction – The charging of an object through direct contact
h) Induction – The separating of charge without making direct contact
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4) The Electroscope – A device that can detect small amounts of electrical charge
a) Charging an electroscope through CONDUCTION causes it to gain the SAME charge as the charging material
b) Charging an electroscope through INDUCTION causes it to gain the OPPOSITE charge as the charging material
5) Coulomb’s Law – Opposite charges attract; like charges repel each other
a)
i)
(1)
-
ii)
iii) The same force is felt by BOTH charges
6) Electric Fields
a)
i)
b) Always points AWAY from Positive and TOWARD Negative charges
c) Electric Field lines CANNOT cross
d) Electric Field inside a conductor is equal to zero
e) Electric Field around a SINGLE CHARGED PARTICLE
i)
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f)
Electric Field between PARALLEL PLATES
i)
(1)
(2)
ii) The Electric field is constant between parallel plates
7) Electric Potential/Potential Difference/Voltage
a) The change in potential energy, or work done, per unit positive test charge
b)
i)
c) Electrical Potential for a SINGLE CHARGE
i)
d) Electrical Potential Energy Equation
i)
e) The Electron Volt
i) The kinetic energy acquired by an electron or proton accelerated
through 1 Volt
ii)
(1)
f)
-
Equipotential Lines
i) Diagrams of how electrical potential is oriented in a field
ii) Always perpendicular to the Electric Field Lines
iii) Positive voltages produce “hills” while Negative voltages produce “valleys”
iv) The surface of a conductor is always an equipotential surface
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8) The Capacitor – A device for storing electrical charge and energy consisting of two oppositely charged plates
a) Capacitance – The amount of charge that can be stored on the plates per volt
Circuit Symbol
b)
i)
(1) The Farad is very large value so it is usually µF (10-6F) or pF (10-9F)
ii)
iii)
iv)
-
(1) Putting a material between the two plates will always increase capacitance
c) Energy Stored
i)
CIRCUITS
1) Current – The flow of electrons
a)
i)
b) Conventional Current
i) In actuality electrons flow through the circuit but all problems use Conventional Current; the flow of positive
particles
2) Resistance – Opposes the flow of electrons
a)
i)
ii)
iii)
iv)
b) Resistance depend on three characteristics:
i) Material: Different materials have different resistivities
ii) Length: Longer length increases resistance
iii) Cross Sectional Area: Thicker wires decrease resistance
iv) Temperature: Higher temperature increases resistance
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3) Circuit Symbols
Component
Circuit Symbol
Component
Battery
Switch
Wire
Ground
Resistor/Bulb
Capacitor
Voltmeter
Ammeter
Voltmeter
Connection
Ammeter
Connection
Circuit Symbol
4) Ohm’s Law
a)
5) Watt’s Law – Circuit Power
a)
i)
6) Electromotive Force (emf) – The potential difference between the two terminals of a power source; such as a
battery
a) emf when no current is flowing
i)
(1)
b) emf when current flows through the terminals
i)
(1)
7) Electrical Energy
a)
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8) Series Circuits – Only one path for electricity to flow through
a)
b)
c)
d)
e)
9) Parallel Circuits – Multiple paths for electricity to flow through
a)
b)
c)
d)
e)
10) Kirchoff’s Rules
a) Junction Rule – At any junction, the sum of all the current entering the junction must equal to the sum of all
currents leaving the junction
b) Loop Rule – The sum of the changes in potential around any closed path of a circuit must be zero
MAGNETISM
1) Magnetic Field
a) A magnetic field is produced by moving charged particles
b) The magnetic field always points FROM the North pole and TOWARDS
the South pole
i) Like poles repel while opposite poles attract each other
c)
d)
2) Right Hand Rule – Used to determine the direction of Conventional Current
Flow, Magnetic Field and the Magnetic Force
a) Thumb – Points in the direction of the Current Flow
b) Outstretched Fingers – Point in the direction of the Magnetic Field
c) Open Palm – Points in the direction of the Magnetic Force
i) *NOTE* - This rule is used when the current or the particle has a POSITIVE CHARGE! If the current or particle
has a NEGATIVE CHARGE then use the LEFT HAND instead!
3) Magnetic Force on a Moving Charged Particle
a)
b) Hand Rule
i) Thumb points in direction of particle’s Velocity
ii) Fingers point in direction of the Magnetic Field
iii) Open Palm points in direction of Magnetic Force
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4) Mass Spectrometer – A device that measures the mass of an atom
a)
5) Magnetic Flux – Magnetic Field Lines
a)
i)
ii)
iii)
6) Magnetic Field Around a Current Carrying Wire
a)
i)
ii)
iii)
-
b) The above equation can be used for a closed circle loop of wire as well
c) Hand Rule
i) Thumb points in direction of current flow
ii) Fingers WRAP AROUND the wire indicating the direction of the magnetic field
7) Magnetic Force on a Current Carrying Wire
a)
b) Hand Rule
i) Thumb points in direction of the current
ii) Fingers point in direction of magnetic field
iii) Open palm points in the direction of magnetic force
8) Magnetic Force Between Two Parallel Current Carrying Wires
a)
b) Currents going in the SAME direction produce an ATTRACTIVE force
between wires
c) Currents going in the OPPOSITE direction produce a REPULSIVE force
between wires
9) Magnetic Field at the Center of a Solenoid
a) Solenoid – A series of looped wire
b)
i)
ii)
c) Hand Rule
i) Thumb points in direction of the North Pole
ii) Fingers wrap in the direction of the current
d) Adding a permeable core, like iron, to the solenoid will increase the Magnetic Field Strength
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ELECTROMAGNETIC INDUCTION
1) Electromagnetic Induction – Production of electricity caused by motion between a Magnetic field and a conductor
that cuts through the flux lines
2) Faraday’s Law – Changing magnetic fields create an electric potential in a conductor
a)
3) Lenz’s Law – An induced emf in a wire loop or coil has a direction such that the current it creates produces its own
magnetic field that opposes the change in magnetic flush through the loop or coil
a) A form of the Conservation of Energy Law
4) emf Produced by a Moving Wire
a)
b) Hand Rule
i) Thumb points in the direction of the Current
ii) Fingers point in the direction of the Magnetic Field
iii) BACK OF THE HAND points in the direction of the wire’s velocity
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