Direct Current Circuits
- Direct Current Circuits
- source of emf (E)
- maintains current
- work done/charge
- battery
- emf vs terminal voltage
- internal resistance (r)
- Resistors in Series
- replace combination with Req
- I = I1 = I2
- same current flows through all resistors
V = Ireq- V = V1 + V2
- V = V1 + V2
- V1 = I1R1; V2 = I2R2
- Ireq = I1R1 + I2R2
- Req = R1 + R2
- Req = R1 + R2 + R3 + ...
- Req > R1, R2, R3,
- Resistors in Parallel
- replace combination with Req
- V = V1 = V2
- same potential difference across each resistor
- V = Ireq
- I = I1 + I2
- I = I1 + I2
- I1 = V1/R1; I2 = V2/R2
- V/Req = V1/R1 + V2/R2
- 1/Req = 1/R1 + 1/R2
- 1/Req = 1/R1 + 1/R2 + 1/R3 + ...
- Req < R1, R2, R3,
- Combinations
- Find equivalent resistance of smallest pure series or parallel
- Continue process until you have reduced the combination to one equivalent
resistance
- Kirchhoff's Rules
- Junction Rule (Conservation of Charge)
- The sum of the currents entering a junction equals the sum of the
currents leaving the junction.
- Loop Rule (Conservation of Energy)
- The sum of the potential differences across all the elements in a
closed loop is equal to zero.
- Each branch will have different current
- pick variable and direction for current in each branch.
- Pick direction of travel around loop.
- Two components:
- When traveling around loop:
- Resistors
- -IR if moving in same direction as current
- +IR if moving in opposite direction of current
- (depend on chosen direction for current)
- sources of emf
- +V if moving from - terminal to + terminal
- -V if moving from + terminal to - terminal
- (do not depend on chosen direction for current)
- Examples
