Science w/ Ms. Hendryx 12/6/11

1.Write the 4 kinematic equations. 2.Estimate to the nearest order (power of 10): a)The number of meters in 1474 kilometers b)The number of meters in 36 millimeters c)The number of milligrams in a kilogram 3.What are the units of: a.Resistance? b.Current?

What do we know about electricity?

VOCABULARY: Charge, q Current, I Resistance, R Electric Potential (Voltage), V Capacitance, C An inherent measure of an object, + or - [Coulombs, C] The flow of charge [Amperes, Amps, A; A=C/s] Opposition to the flow of charge [Ohms, Ω] Electrical potential energy per charge [Volts, V] Ability of an object to hold stationary charge [Farads, F]

Electrical Potential Energy + (How much the charge wants to move) (Acts on a charge to make it move)

Electric Potential Voltage (electrical energy per charge) (Think of a mountain top—higher V is like a higher elevation)

Symbols: Current Voltage bias (difference) Resistance Capacitance ΔVΔV + - I R C

ΔV = IR Ohm’s Law: ΔV=5 VR = 100 Ω I = ? What direction does the current flow?

Power Law: P = IΔV = I 2 R = ΔV 2 /R Units: Watts A 9V battery in a circuit produces 45 mW of power. What is the total current across the circuit? What is the resistance in the circuit?

Rules we live by in Circuit Land: 1.The Junction Rule (Conservation of Charge): When the circuit splits, so does the current. I in = I 1 +I 2 +…= I out It doesn’t have to split evenly!!! I in I1I1 I3I3 = I2I2 I out

Rules we live by in Circuit Land: 2. The Loop Rule (Conservation of Energy): The total voltage difference across a closed circuit (loop) is zero. ΔV loop = ΔV battery +ΔV 1 + ΔV 2 +…= 0 Treat every resistor as its own ΔV!! ΔV2ΔV2 ΔV1ΔV1 ΔV3ΔV3 ΔV batt =++

ΔV = IR R = ? R = the “equivalent resistance”

ΔV = IR R = ? V I In series, R = R 1 + R 2 + R 3 + … In a closed loop, the voltages add, so V = IR 1 + IR 2 + IR 3 +…

ΔV = IR R = ? In parallel, (because the current is dividing) I In a closed loop, the voltages add to 0, so ΔV = IR = I 1 R 1 = I 2 R 2 = I 3 R 3 Currents add at junctions, so I = I 1 + I 2 V/R = V/R 1 + V/R 2

C = Q/ ΔV C = Capacitance Q = charge ΔV = Voltage d A ΔVΔV

C = Q/ ΔV d A ΔVΔV E = (1/2)C( ΔV) 2 = (1/2)QV Only charge from 1 plate

C = ε 0 A/d C = Capacitance ε 0 = permittivity of free space A = Area d = Separation Distance d A ΔVΔV