Chapter 5 Parallel Circuits LESSONS

(L1)If two 6-volt sources are connected in parallel to supply a 24-ohm load and the total current is 0.25 A, how much current would each source supply to the load? (Round the FINAL answer to three decimal places.)

.125 Divide 0.25 amps between the two power sources. Source current equals total current divided by number of power sources shown by the formula: Is=It/Ns Is=0.25amps/2sources Is=.125amps Each power source supplies .125amps of current.

(L1)What fraction of the total current that is supplied to the load would be provided by each of four equal rated batteries connected in parallel to the load?

1/4

(L1)Find the total current in the circuit with the switches in the position shown.

Because the switch is open, no current will flow to lamp 3. First, calculate individual currents only at lamps 1, 2, and 4. Current at lamp 1 equals total voltage divided by resistance of lamp 1: IL1=Et/RL1 IL1=100volts/100ohms IL1=1amp Since the resistance values are the same for lamp 2 and 4, the current will be 1 amp in each branch using the same formula. Second, calculate total current using the sum rule: Total current equals current at lamp 1 + lamp 2 + lamp 4 It=IL1+IL2+IL4 It=1 + 1 + 1 It=3amps Total current in the circuit is 3 amps

(L1)T/F: If all lamps draw the same amount of current, closing the switch on Lamp 3 will add 1 amp of current to the circuit.

Current at lamp 1 equals total voltage divided by resistance of lamp 1: IL1=Et/RL1 IL1=100volts/100ohms IL1=1amp. Since the values are all the same for each lamp, 1 amp of current will flow through each lamp as long as the switches are closed. Using the total current sum rule: It= IL1+IL2+IL3+IL4 It= 1 + 1 + 1 + 1 It= 4amps True. Closing the switch will add 1 amp of current.

(L1)T/F: Adding parallel loads to a circuit will increase total circuit resistance and increase the total circuit current.

False. Adding parallel loads to a circuit will *decrease* total circuit resistance and increase the total circuit current.

(L1)T/F: Branch currents are always greater than total current.

False. Branch currents are always less than total current.

(L1)Find the total current in the circuit (Round the FINAL answer to two decimal places.)

First, calculate current at each lamp using known applied voltage of 120 volts: Current at lamp 1 equals power at lamp 1 divided by total voltage formula: IL1=PL1/Et IL1=100watts/120volts IL1=0.833333333amps Current at lamp 2 equals power at lamp 2 divided by total voltage formula: IL2=PL2/Et IL2=250watts/120volts IL2=2.083333333 Current at lamp 3 equals power at lamp 3 divided by total voltage formula: IL3=PL3/Et IL3=25watts/120volts IL3=0.208333333 Second, calculate total current using the sum rule: It=IL1+IL2+IL3 It=0.833333333 + 2.083333333 + 0.208333333 It= 3.124999999999999 Total current in the circuit is 3.12amps

(L1)In this circuit, two 47-ohm load resistors are connected in parallel with a 12-volt supply. What is the total number of 47-ohm resistors (including the first two) that can be connected without blowing the 2-amp fuse?

First, calculate how much current will flow in a branch with a 47ohm resistor. Current through a resistor equals total voltage divided by resistance: I=Et/R I=12volts/47ohms I=0.255319149amps Current through ONE 47ohm resistor is 0.26amps. Second, find the max number of 47ohm resistors that can be added in parallel if each allows 0.26amps of current to flow. Max number of resistors equals max current allowed divided by the current flow of each resistor: N=I[MAX]/I[R] N=2amp fuse/0.26amp of resistor N=7.692307692 The max number of 47ohm resistors that can be added in parallel and NOT blow a 2amp fuse is 7 resistors. 7resistorsx0.26amps=1.82amps 1.82amps total is less than the 2 amp rating of the fuse, so we're safe :)

(L1)Find the total current in the circuit.

First, find the current in each branch using the known applied voltage value of 98 volts: Current at resistor 1: IR1=Et/R1 IR1=98volts/28ohms IR1=3.5amps Current at resistor 2: IR2=Et/R2 IR2=98volts/70ohms IR2=1.4amps Second, find total current using the sum rule: It=I1+I2 It=3.5amps+1.4amps It= 4.9amps Total current is 4.9amps.

(L1)A circuit has a 24-volt supply and four identical resistors in parallel. If the total equivalent circuit resistance is 5 ohms, what is the current in each branch of the circuit? (Round the FINAL answer to one decimal place.)

First, find total current in the circuit. Total current equals total voltage divided by total resistance: It=Et/Rt It=24volts/5ohms It= 4.8amps Total current in the circuit is 4.8 amps. Second, divide 4.8 amps among 4 resistive branches: Current in a branch equals total current divided by the number of branches: IB=It/Nb IB=4.8amps/4branches IB=1.2 amps Each branch has 1.2amps of current.

(L1)Find the total current in this circuit.

First, solve for current in each branch: IR1=Et/R1 IR1=66volts/110ohms IR1=.6amps IR2=Et/R2 IR2=66volts/2200ohms IR2=.03amps IR3=Et/R3 IR3=66volts/5.5ohms IR3=12amps Second, find total current in the circuit using the sum rule: It=IR1+IR2+IR3 It=.6 + .03 + 12 It=12.63amps Total current in the circuit is 12.63 amps

(L1)What formula is used to find total current when total resistance and applied voltage is known?

It=Et/Rt

(L1)What is the formula for total current when branch circuits are known?

It=I1+I2+I3+...In

(L1)Calculate the branch current which would be shown on Ammeter M2 in the circuit.

To find current at M2, you need to know the applied voltage in the circuit. Since voltage is the same throughout a parallel circuit, you can find the voltage E1 at R1. First, solve for E1 at R1 using the formula: Voltage at R1 equals current at R1 times resistance of R1 ER1=IR1xR1 ER1=7.5amps x 3.6ohms ER1= 27 volts Second, now that you have applied voltage, solve for E2 at R2 using the formula: Current at R2 equals voltage at R2 divided by resistance of R2 IR2=ER2/R2 IR2=27volts / 2.7ohms IR2=10amps The reading at M2 is 10 amps.

(L1)The current that leaves and re-enters the power source is called the:

Total Current

(L1)T/F: A break in any branch of a parallel circuit will cause a decrease in the total current of the circuit.

True

(L1)If a circuit has three branches with branch currents of 10 amps, 5 amps, and 12.5 amps, what would be the total circuit current? (Round the FINAL answer to one decimal place.)

Using formula for total current when branch currents are known: It=I1+I2+I3 It=10A+5A+12.5A It=27.5Amps Total current is 27.5amps

(L1)If two 6-volt sources are connected in parallel to supply a 24-ohm load, how much current will flow in the circuit? (Round the FINAL answer to two decimal places.)

Using the formula for total current when applied voltage and total resistance are known: It=Et/Rt It=6volts/24ohms It=.25Amps Total current in the circuit will be .25amps *Et, or total voltage, is 6 volts because when multiple power sources with the same voltage are connected in parallel, the applied voltage is the same throughout the circuit.

(L1)What is the total resistance for the circuit?

Using the product over sum rule: Rt=(R1xR2)/(R1+R2) Rt=(28x70)/(28+70) Rt=1960/98 Rt=20ohms Total resistance is 20ohms.