Unformatted text preview: Currents and Resistors
Q = n q Avd Current: I = t
Current Density:
Va
E Batteries J = nqvd J= I = n q vd A L Vb
I e Resistance: R=
dR = V I dL
A R= L
A Resistivity: E = J Resistivity: Parallel: Series: R = dR Const. V Ceq, parallel =
i Ci 1
Const. V Const. I 1 Ceq, series Wednesday, 14 February 2007 Const. Q =
i 1 Ci Req, parallel =
i 1 Ri
Ri Req, series =
i 1 Wednesday, 14 February 2007 2 Question
The power company bills you based on the number of kW*hr used. This is a unit of A. Power B. Energy Real batteries have an internal resistance which affects their behavior "Load" Load" Real Batteries U energy Power (W ) = t time C. Charge D. Speed energy kW hr = time = energy time r & R are in series: V = I (r + R ) emf & (r & R) are in parallel: = V = I (r + R)
Small I Big I VAB =  Ir = IR
Big R Small R VAB VAB < 4 Wednesday, 14 February 2007 3 Wednesday, 14 February 2007 1 Question
Batteries are rated in Amp*hr. What kind of unit is this? Making Measurements in Circuits Ammeter: measures current Voltmeter: measures potential difference Ohmmeter: measures resistance Applies a know V, measures I, and calculates R A. Power B. Energy Current(Amp) =
Amp hr = Q charge t time C. Charge D. Speed charge time = charge time Meters should impact the circuit that they are measuring as little as possible! possible!
5 Wednesday, 14 February 2007 6 Wednesday, 14 February 2007 Question
An ideal Ammeter:
A. Has infinite resistance B. Has zero resistance Question
An ideal Voltmeter:
A. Has infinite resistance B. Has zero resistance C. Is placed "in line" as if it is part of the wire line" D. Is placed "across" a circuit element, like a resistor, across" capacitor, or battery E. Both B and C
7 C. Is placed "in line" as if it is part of the wire line" D. Is placed "across" a circuit element, like a resistor, across" capacitor, or battery E. Both A and D
8 Wednesday, 14 February 2007 Wednesday, 14 February 2007 2 Find I and V through each resistor
2 Sample Circuit Find I and V through each resistor
1 Sample Circuit
Series: Constant I R27 = 2 + 7 = 9 Parallel: R236 Constant V
1 1 1 1 = + + 2 3 6 = 1
9 Series: Constant I R15 = 1 + 5 = 6
1 I total = Req = 18V = 2A 9 6 Parallel: R36 = + 3 6 Constant V 1 1 = 2 Wednesday, 14 February 2007 9 Wednesday, 14 February 2007 10 3 ...
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 Fall '07
 JapGuy
 Resistor, Electrical resistance, Wednesday, A. Power B., infinite resistance B.

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