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Physics chapter 22 & 23
Chapter 22 & 23Electricity & Circuits
Ohm’s Law Ohm’s Law - The resistance does not depend on the voltage or the current flowing through the circuit. ∆V = I R ∆V = Potential difference or Voltage drop = V, volts I = Current = A, amps R = Resistance = Ω, ohms
Charge in circuitsq = It Coulomb =C=As or A = C/s Elementary charge 1.6 X 10-19 C
Power Power is the rate of doing work. Power is the rate at which energy is transferred. It is measured in Watts. P= ∆E P = Power = W = J/s t P = I ∆V P = I2 R P = (∆V)2 R
Measurements Ohmeter measures resistance in ohms (Ω) – Hook up in parallel outside circuit Voltmeter measures voltage in volts (V) – Hook up in parallel with circuit running Ammeter measures current in amps (A) – Hook up in series. Remove a wire in the circuit and place ammeter in its place.
Series Circuit – one current path The Equivalent Resistance is greater than the largest resistor RT = R1 + R2 + ... The current is the same in each element since there is only one current path IT = I1 = I2 = ... The total voltage is the sum of the individual voltages and should equal the voltage of the battery ∆VT = ∆V1+ ∆V2+...
Parallel Circuit – more than one path The Equivalent Resistance is less than the smallest resistor 1/RT = 1/R1 + 1/R2 + … The total current is the sum of the individual currents IT = I1 + I2 + ... The voltage drop is the same across each resistor because they each have a path from the battery ∆VT = ∆V1 = ∆V2 = ...
Adding a Resistor to a Circuit Add a resistor in series 1) total resistance increases 2) therefore, current must go down Add a resistor in parallel 1) total resistance decreases 2) therefore, current must go up
Solving Series and Parallel Circuits Calculate the total resistance. Calculate each parallel branch resistance then add the remaining series branches. Make simplified equivalent circuit drawings in order to solve the circuits. Calculate the total current Use the total current as the current to the series part of the circuit to calculate its voltage drop. Calculate the parallel voltage drop by subtracting the series drop from the total voltage drop. Use a chart to track what is known/unknown.