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55 Cards in this Set
- Front
- Back
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charge unit? charge
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smallest unit of charge, e = 1.6e-19 C = charge of 1 electron (-) or proton (+)
current runs in opposite direction of electrons (-) charge = q (units of coulombs C) it is quantized, which means any charge must be at least as large as certain smallest unit opposite charges attract each other, like charges repel each other |
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universal law of conservation of charge
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universe has zero net charge
net charge is created by separating electrons from protons anytime a positive charge is created, a negative charge is created as well |
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Coulomb's law
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F = kq1q2/r^2
k: coulomb constant = 9e9 N*m^2/C^2 q: respective charges r: distance between centers of charge describes magnitude of force of repulsion or attraction between 2 charged objects analogous to gravitation force formula force due to gravity is negligible compared to force due to charge |
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center of charge
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point from which charge generated by object or system can be considered to originate
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field
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man-made concept designed to explain action at a distance
forces created by fields can act at a distance |
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lines of force
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can represent any field
lines point in direction of field lines point positive to negative for electric field lines point towards the mass creating the field for gravitational fields relative distance between lines indicate strength of field closer the lines, the stronger the field lines of force can never intersect!! no lines of forces inside a uniformly charged sphere |
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electric field (E)
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electrostatic force per unit charge (units of N/C or V/m)
E is a vector, and points in direction of field (+ charge to - charge). Use vector addition in summing fields A charge (q) emits an electric field (E) |
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electric field of point charge
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E = kq1/r^2
system of point charges: summing (vector addition) of each electric field for each charge E in units of N/C or V/m |
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force on charge in electric field
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F = Eq
F: force E: electric field q: charge |
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potential energy (U) of charge in electric field
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U = Eqd
U: potential energy E: electric field q: charge d: displacement Within an electric field, movement perpendicular to the field doesn't result in a change in potential. |
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electric potential energy
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U = kq1q2/r
U: electric potential energy (in joules) k: coulomb constant q: charge r: distance between charges If the electric field is created by a point charge, the electric potential energy can be derived from this equation. |
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voltage (V) definition, units, equation?
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potential of the field
potential for work by an electric field in moving any charge from 1 point to another V = Ed V: voltage (volts, V), scalar or J/C E: electric field d: displacement |
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voltage due to point charge
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V = kq1/r
voltage due to group of point charges: voltage due to each individual charge is summed directly |
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work due to electric field
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W = mgh or W=qEd
The work done by a field is path independent |
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equipotential surfaces
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the surface normal to electric field that describes set of points all with same potential
all points are same voltage |
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electric dipole
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created by 2 opposite charges with equal magnitude
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conductors
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allow electrons (-) to flow relatively freely
good conductors of electricity, poor resistors such as metals The electric field inside a charged conductor is 0, charge is on the surface though |
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resistors
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poor conductors but good resistors
hold electrons tightly in place such as: networks solids such as diamond and glass |
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induction
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ability to charge a conductor because of easy flow of electrons
1. if negatively charged object is moved close to electrically insulated conductor, electrons on conductor will repel to opposite side 2. touch conductor with 2nd conductor, electrons will repel further and move to 2nd conductor 3. remove 2nd conductor, 1st conductor has less electrons than protons (induced positive charge) |
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current (i)
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moving charge
given in amps (A) or C/s scalar, flow in direction of movement of positive charge because electrons were designated as negative charge, current created by flowing electrons is in opposite direction of flow of electrons flow of electrons resembles fluid flow |
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circuit
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cyclical pathway for moving charge, requires a complete circle
At end of system V=0 |
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resistivity (p)
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quantitative measure of property that all substances resist flow of charge
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resistance (R)
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quantitative measure of an object of a particular shape and size to resit flow of charge
measured in ohms |
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Ohm's law
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product of resistance and current
V = IR V: voltage (analogous to gh) I: current R: resistance |
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Kirchoff's 1st rule
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amount of current flowing into a node (any intersection of wires) must be same amount that flows out
rate at which fluid flows into an intersection must match rate at which fluid flows out |
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kirchoff's second rule
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voltage around any path in a circuit must sum to zero
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electromotive force (EMF)
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not a force, but instead the voltage provided by battery
A battery adds energy to a circuit by increasing the voltage from 1 point to another |
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capacitor
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used to temporarily store energy in a circuit
stores it in the form of separated charges |
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parallel plate capacitor
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2 plates made from conductive material are separated by a very small distance
on a charged capacitor, 1 plate holds positive charge and the other holds same amount of negative charge (discharge when + moves to -) The separation of charge creates an electric field that is constant everywhere between the plates |
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capacitance
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the ability to store charge per unit voltage
something with high capacitance can store a lot of charge at low voltage C = Q/V C: capacitance Q: charge of plate V: votlage |
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energy stored by capacitor
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U = 1/2QV
U = 1/2CV^2 U = 1/2Q^2/C U: energy stored Q: charge V: voltage C: capacitance |
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dielectric constant (K)
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refers to substance between plates of capacitor
substance must be an insulator, otherwise it would conduct electrons from 1 plate to the other, not allowing any build up of charge acts to resist creation of electric field, allowing capacitor to store more charge (greater capacitance) higher K means greater capacitance Kvacuum = 1 limits value of possible voltage across plates, at max voltage K will breakdown and conduct electricity work is done on K and energy is stored in K |
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Series
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components lined up in row, like train cars
any 2 components not separated by a node |
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parallel
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single components in alternate paths connecting same node
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resistor in series
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total resistance (effective resistance, Reff) is sum of resistances
Reff = R1 + R2 + R3 + ... |
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Resistor in parallel
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1/Reff = 1/R1 + 1/R2 + 1/R3 + ...
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Capacitors in series
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1/Ceff = 1/C1 + 1/C2 + 1/C3 +...
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Capacitors in parallel
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Ceff = C1 + C2 + C3 + ...
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Power (3 formulas?)
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same quality as mechanical power (Unit = J/s)
P = IV P = I^2R P = V^2/R P: power I: current V: voltage R: resistance As current goes through resistor, heat is generated. The rate at which heat is generated by current as it flows through resistor is equal to power dissipated |
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Direct current (DC current)
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net movement of electrons is in one direction around circuit
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Alternating current (AC current)
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created by oscillating electrons back and forth in simple harmonic motion
voltage or current can be described by sine wave since movement of electrons creates power regardless of direction, electrons do not have to be driven in one direction current commonly used in home outlets |
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Max current in AC current occurs when?
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occurs when electrons are at max velocity. RMS is the average value for any max current, voltage, or power generated by AC current.
Irms = ((√2)/2))*Imax Imax: max current Irms: root mean square current |
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Max voltage
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Vrms = ((√2)/2))*Vmax
Vmax: max voltage Vrms: root mean square voltage |
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RMS
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root mean square
square root of average of squares square all terms, take average, then take square root average value of sine wave = 0 Vrms = 120V --> Vmax = 170V |
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magnetic fields (B)
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generated by moving charge, which experiences force when moving through a magnetic field
similarities to electric fields, measured in units of Telsa (T) north and south poles; like poles repel and opposite poles attract, poles never exist separately can be represented by lines of force, point from N to S pole (earth's magnetic field points in opposite direction) created by changing electric field, thus changing magnetic field creates electric field stationary charge doesn't create magnetic field but a moving charge (current) does |
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Right hand rule (RHR)
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predicts direction of magnetic field due to current carrying wire
thumb: direction of current fingers: grab wire, direction in which fingers wrap around wire is direction of magnetic field |
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force experience by charge moving through magnetic field
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F = qvBsin0 = mv^2/r (find radius of curvature)
F: force q: charge v: velocity B: magnetic field 0: angle between magnetic field and velocity force is directed perpendicularly to both velocity and magnetic field, therefore does not work, leaving only 2 possible directions for force RHR thumb: direction of moving positive charge fingers: direction of magnetic field palm: direction of force negative charge reverses direction of force |
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Faraday's law of induction
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a changing magnetic flux induces an EMF (E) and a current, which creates an induced magnetic field
forces due to induced electric field (EMF) are nonconservative, thus mechanical energy is transferred to internal energy |
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Lenz's law
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induced current will create a magnetic field opposing induced magnetic field
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electric fields due to point charge equations
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F = kq1q2/r^2
U = kq1q2/r E = kq1/r^2 V = kq1/r |
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constant electric fields equations
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F = Eq
U = qEd = Fd = Vq V = Ed |
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Resistors equations
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V = IR
P = IV P = I^2R P = V^2/R Series: Reff = R1 + R2 +... Parallel: 1/Reff = 1/R1 + 1/R2 +... |
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Capacitors equations
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C = Q/V
U = (1/2)QV U = (1/2)Q^2/C U = (1/2)CV^2 Series: 1/Ceff = 1/C1 + 1/C2 +... Parallel: Ceff = C1 + C2 +... |
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AC current equations
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Vmax = square root (2Vrms)
Imax = square root (2Irms) |
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magnetism equations
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F = qvBsin0
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