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40 Cards in this Set
- Front
- Back
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What is an electric field?
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describes a force for any charge in its field.
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What is the direction of an electric field?
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positive to negative
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Equation for how electric field is related to force
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F=qE
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Coulomb's Law equation
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F=(kq1q2)/(r^2)
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When is Coulomb's Law used?
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It is used to find the force caused by point charges.
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What does Gauss' Law describe?
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It describes flux.
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What is flux?
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It is the amount of field that passes through a given area.
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What is the general equation for electric flux?
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EA = qin/E0
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What is the Gaussian equation for a point charge? Describe how it was derived.
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For a point charge, the gaussian surface is a sphere around the charge. If flux is EA = qin/E0, and area is 4*pi*r^2, then :::
E = kq/r^2 |
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What is the Gaussian equation for a line of charge? How was it derived?
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The gaussian surface is a cylinder. So the surface is 2*pi*r*l. q/l = charge density = lambda. So:
E = lambda/(2*pi*r*E0) |
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What is the Gaussian equation for a parallel plate capacitor? What is the equation for a single sheet of charge?
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For a parallel plate capacitor :
E = sigma/E0 where sigma = charge density = charge per unit area Equation for a single sheet : E = sigma / 2E0 there is a two because for a single sheet, there are two cylinders through which the charge passes through, doubling the area. |
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The electric field is (weakest / strongest) near the sharp points of a conductor.
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strongest. as area decreases, electric field increases based on the electric flux equation
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Define capacitance
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it is the charge stored per given potential. this is specific to a capacitor
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What is the equation for capacitance that relates it to potential and charge?
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Q=CV
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What is a dielectric? How does it work?
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Dielectric is the substance in between the plates of a capacitor that can be polarized and allow the capacitor to hold more charge. A dielectric increases capacitance.
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What is the equation for capacitance that relates it to the dielectric, etc?
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C = (KE0A)/d
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What is current?
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It is the flow of charge. It is the "velocity" of charge. charge per second
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What is the equation for current?
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I = q/t
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What is the rule for combining resistance in series? Why?
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Reff = R1 + R2
Resistors are combined directly because in series, current is kept constant. so V1/I1 + V2/I2 gives total resistance. |
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What is the rule for combining resistance in parallel? Why?
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1/Reff = 1/R1 + 1/R2
The inverses are added because in parallel, voltage is kept constant, so resistance depends on adding the inverse of the currents. |
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What is the rule for capacitors in series? Why?
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1/Ceff = 1/C1 + 1/C2
This is because in series, charge is what changes, so Ceff = Q/V. Adding the voltages gives Ceff, so you have to add the inverses. |
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What is the rule for capacitors in parallel?
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In parallel, potential is kept the same while charge changes. So Ceff = C1 + C2.
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What is the junction rule?
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total current going in a junction = total current going out. Follows the conservation of charge.
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What is the loop rule?
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a loop is a closed circuit, and the net voltage drop around a closed loop is 0. This means that the net potential gains = net potential drops. Follows law of conservation of energy.
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What is the equation for a time constant?
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T=RC
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What is the equation for charging a capacitor?
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Q=Qmax(1-e^(-t/RC))
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What is the equation for discharging a capacitor?
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Q=Qo(e^(-t/RC))
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Current (increases/decreases) with time with a capacitor
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decreases
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Charge (increases/decreases) with time with a capacitor.
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increases
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Current is at a max when time is (0/infinity) while charge is at a max when time is (0/inf)
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0, infinity
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What are five variables that are used in circuits?
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charge (Q), current (I), potential or voltage (V), resistance (R), capacitance (C)
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What is the equation for voltage in terms charge and capacitance?
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∆V = Q/C
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What is the equation for voltage in terms of current and resistance?
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V=IR
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What is the equation for resistance in terms of resistivity?
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R=p(L/A)
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What is the equation for work?
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W = q∆V
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What is the equation for power?
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P=IV
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equation relating electric field and voltage
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E=V/d
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basic equation for potential energy stored in a capacitor
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U=(qV)/2
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equation relating electric potential energy and work
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W=∆EPE
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equation relating voltage, charge, and distance
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V=kq/r
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