1. Parallel Circuits

2. Parallel Circuit
A parallel circuit is a circuit with more than one path for the current.

4. Parallel Circuits Each path in the circuit is called a branch.
The current through a branch is called the branch current.

5. Kirchhoff’s Law
All current flowing into a branch point must flow out again.
Branch points are called circuit nodes.

6. Voltage & Current in a Parallel Circuit
The voltage is the same across each branch of a parallel circuit.
The total current is equal to the branch currents added together.

8. All of the electrical outlets in Jonah’s living room are on one parallel circuit. The circuit breaker cuts off the current if it exceeds 15 amps. Will the breaker trip if he uses a light (240 Ω), stereo (150 Ω), and an air conditioner (10 Ω)?
Because the devices are plugged into electrical outlets, the voltage is 120 volts for each.
Ilight=(120 V)/(240 Ω)=0.5 A
Istereo=(120 V)/(150 Ω)=0.8 A
IAC=(120 V)/(10 Ω)=12 A
The total is 13.3 A, so the circuit breaker will not trip.

9. Req for 6.0  and 2.0  Req for 8.0  and 4.0 
Answer: 8.0 
Req for 8.0  and 4.0 
Answer: 2.7 
Req for 3.0  and 6.0  and 2.7  and 1.0 
Answer: 12.7 
So, the resistance of all 6 resistors is equivalent to a single 12.7  resistor.
To find the equivalent resistance for the circuit shown above, follow the steps shown to the right:
For problems, it is a good idea to go through the steps on the overhead projector or board so students can see the process instead of just seeing the solution. Allow students some time to work on problems and then show them the proper solutions. Do not rush through the solutions. Discuss the importance of units at every step. Problem solving is a developed skill and good examples are very helpful.
These problems are complex and are very difficult to solve without redrawing the circuit as each Req is calculated, and then using all of the equivalent circuits drawn to solve the problem.

10. Use the parallel circuit pictured below to answer questions (a) - (d).
a. What is the voltage across each bulb?
b. What is the current in each branch?
c. What is the total current provided by the battery?
d. Use the total current and the total voltage to
calculate the total resistance of the circuit.

11. Find the equivalent resistance, the total current drawn by the circuit, and the current in each resistor for a 9.00 V battery connected to:
One 30.0  resistor
Three 30.0  resistors connected in parallel
Answers:
30.0 , A, A
10.0 , A, A
For problems, it is a good idea to go through the steps on the overhead projector or board so students can see the process instead of just seeing the solution. Allow students some time to work on problems and then show them the proper solutions. Do not rush through the solutions. Discuss the importance of units at every step. Problem solving is a developed skill and good examples are very helpful.
Point out that the current in each bulb is the same for one bulb as it is for three bulbs. This is a consequence of the PE lost being the same for each bulb. The electrons’ potential difference drop is 9.00 V for every bulb.
Ask students how the brightness of the three bulbs would compare to that of the single bulb. Since current and potential difference are the same, all three bulbs would be as bright as the single bulb.