lectric Circuits - Detailed Help

Assignment EC12: Parallel AND Series Circuits Calculations

Objectives:
  • The student should be able to identify a circuit as being either parallel or series and mathematically analyze the circuit to determine the equivalent resistance, the total circuit current, the voltage drop across each resistor, and the current through each resistor (if given the battery voltage and the resistance of each resistor).

 

Reading:

The Physics Classroom, Circuits Unit, Lesson 4, Part c

The Physics Classroom, Circuits Unit, Lesson 4, Part d

 

 

Three resistors are connected in parallel. If placed in a circuit with a 120-Volt power supply, determine the equivalent resistance, the total circuit current, and the voltage drop across and current through each resistor. Enter your answers to the third decimal place.


Often times, success in physics demands that you have the proper approach - a good game plan. The following strategy should serve you well:

  1. Determine the equivalent resistance of the entire circuit. See Formula Fix section below.
  2. Determine the current in the battery using the equivalent resistance and the battery voltage. The relationship is Ibattery = Vbattery / Req.
  3. The voltage drop across each branch is the same as that in the battery. You can quickly determine the values of V1, V 2 and V 3.
  4. Use the voltage drop and the resistance of each resistor to determine the current through each individual resistor. See first Physics Rules section below.
  5. As a final check, the sum of the current values in each individual branch should equal the overall current. While this check is not necessary, it is a wise habit to perform it in order to quickly catch any errors. See second Physics Rules section below.

 


For parallel circuits, the mathematical formula for computing the equivalent resistance (Req) from the resistance values of the individual resistors (R1, R2, R3, ...) is

1 / Req = 1 / R1 + 1 / R2 + 1 / R3 + ...

 


Branch Currents in Parallel Circuits:

The current in an individual branch of a parallel circuit is dependent upon the voltage drop across the branch and the resistance of the resistor within the branch. The voltage drop across a branch in a parallel circuit is equal to the voltage rating of the battery. Thus, the current in a branch can be calculated as
Ibranch = Vbattery / Rbranch

Current in Parallel Circuits:

Parallel circuits are characterized by branching locations. At each branching location, the current is divided into separate pathways. The overall current approaching the branch is equal to the sum of the current values in each individual branch. This can be expressed in equation form as:
Itot = I1 + I2 + I3 + ...

where Itot is the current outside the branches (and through the battery) and I1, I2 and I3 are the current values in the individual resistors.


What is an effective method of mathematically analyzing a parallel circuit?

 

 

Three resistors are connected in parallel. If placed in a circuit with a 60-Volt power supply, determine the equivalent resistance, the total circuit current, and the voltage drop across and current through each resistor. Enter your answers to the third decimal place.


Often times, success in physics demands that you have the proper approach - a good game plan. The following strategy should serve you well:

  1. Determine the equivalent resistance of the entire circuit. See Formula Fix section below.
  2. Determine the current in the battery using the equivalent resistance and the battery voltage. The relationship is Ibattery = Vbattery / Req.
  3. The voltage drop across each branch is the same as that in the battery. You can quickly determine the values of V1, V 2 and V 3.
  4. Use the voltage drop and the resistance of each resistor to determine the current through each individual resistor. See first Physics Rules section below.
  5. As a final check, the sum of the current values in each individual branch should equal the overall current. While this check is not necessary, it is a wise habit to perform it in order to quickly catch any errors. See second Physics Rules section below.

 


For parallel circuits, the mathematical formula for computing the equivalent resistance (Req) from the resistance values of the individual resistors (R1, R2, R3, ...) is

1 / Req = 1 / R1 + 1 / R2 + 1 / R3 + ...

 

Branch Currents in Parallel Circuits:

The current in an individual branch of a parallel circuit is dependent upon the voltage drop across the branch and the resistance of the resistor within the branch. The voltage drop across a branch in a parallel circuit is equal to the voltage rating of the battery. Thus, the current in a branch can be calculated as
Ibranch = Vbattery / Rbranch

Current in Parallel Circuits:

Parallel circuits are characterized by branching locations. At each branching location, the current is divided into separate pathways. The overall current approaching the branch is equal to the sum of the current values in each individual branch. This can be expressed in equation form as:
Itot = I1 + I2 + I3 + ...

where Itot is the current outside the branches (and through the battery) and I1, I2 and I3 are the current values in the individual resistors.


What is an effective method of mathematically analyzing a parallel circuit?

 

 

Three resistors are connected in parallel. If placed in a circuit with a 30-Volt power supply, determine the equivalent resistance, the total circuit current, and the voltage drop across and current through each resistor. Enter your answers to the third decimal place.


Often times, success in physics demands that you have the proper approach - a good game plan. The following strategy should serve you well:

  1. Determine the equivalent resistance of the entire circuit. See Formula Fix section below.
  2. Determine the current in the battery using the equivalent resistance and the battery voltage. The relationship is Ibattery = Vbattery / Req.
  3. The voltage drop across each branch is the same as that in the battery. You can quickly determine the values of V1, V 2 and V 3.
  4. Use the voltage drop and the resistance of each resistor to determine the current through each individual resistor. See first Physics Rules section below.
  5. As a final check, the sum of the current values in each individual branch should equal the overall current. While this check is not necessary, it is a wise habit to perform it in order to quickly catch any errors. See second Physics Rules section below.

 


For parallel circuits, the mathematical formula for computing the equivalent resistance (Req) from the resistance values of the individual resistors (R1, R2, R3, ...) is

1 / Req = 1 / R1 + 1 / R2 + 1 / R3 + ...


Branch Currents in Parallel Circuits:

The current in an individual branch of a parallel circuit is dependent upon the voltage drop across the branch and the resistance of the resistor within the branch. The voltage drop across a branch in a parallel circuit is equal to the voltage rating of the battery. Thus, the current in a branch can be calculated as
Ibranch = Vbattery / Rbranch

Current in Parallel Circuits:

Parallel circuits are characterized by branching locations. At each branching location, the current is divided into separate pathways. The overall current approaching the branch is equal to the sum of the current values in each individual branch. This can be expressed in equation form as:
Itot = I1 + I2 + I3 + ...

where Itot is the current outside the branches (and through the battery) and I1, I2 and I3 are the current values in the individual resistors.


What is an effective method of mathematically analyzing a parallel circuit?

 

 

Three resistors are connected in series. If placed in a circuit with a 120-Volt power supply. Determine the equivalent resistance, the total circuit current, and the voltage drop across and current through each resistor. Enter your answers to the third decimal place.


Often times, success in physics demands that you have the proper approach - a good game plan. The following strategy should serve you well:

  1. Determine the equivalent resistance of the entire circuit. See Formula Fix section below.
  2. Determine the current in the battery using the equivalent resistance and the battery voltage. See first Physics Rules section below.
  3. Since current is the same in each resistor of a series circuit, you can quickly determine the values of I1, I2 and I3.
  4. Use the current and the resistance of each resistor to determine the voltage drop across each individual resistor. See second Physics Rules section below.
  5. As a final check, the sum of the voltage drops across each individual resistance should equal the battery voltage. While this check is not necessary, it is a wise habit to perform it in order to quickly catch any errors.

 


For series circuits, the mathematical formula for computing the equivalent resistance (Req) from the resistance values of the individual resistors (R1, R2, R3, ...) is

Req = R1 + R2 + R3 + ...

Current in a Series Circuit:

The overall current in a series circuit is no different than the current in an individual resistor. That is, the current through the battery is the same as the current in resistor 1 or resistor 2 or resistor 3 or ... . Since there are no branching locations, current is never divided and is everywhere the same. The amount of current is related to the voltage (Vtot) impressed across the circuit by the battery and the overall equivalent resistance (Req). In equation form, these ideas can be written as
Itot = I1 = I2 = I3 = Vtot / Req

Voltage Drops in a Series Circuit:

Charge gains energy (and electric potential) in the battery and loses energy (and electric potential) in the external circuit. The amount of electric potential gain in the battery is equal to the amount of loss in the external circuit. For series circuits, this loss occurs in a stepwise fashion as the charge passes through each resistor. The sum of the voltage drops across each resistor is equal to the voltage rating of the battery. The voltage drop across an individual resistor within a series circuit can be determined from the resistance of the resistor and the current through the circuit. For example:
V1 = I • R1V2 = I • R2V3 = I • R3

What is an effective method of mathematically analyzing a series circuit?

 

 

Three resistors are connected in series. If placed in a circuit with a 60-Volt power supply. Determine the equivalent resistance, the total circuit current, and the voltage drop across and current through each resistor. Enter your answers to the third decimal place.


Often times, success in physics demands that you have the proper approach - a good game plan. The following strategy should serve you well:

  1. Determine the equivalent resistance of the entire circuit. See Formula Fix section below.
  2. Determine the current in the battery using the equivalent resistance and the battery voltage. See first Physics Rules section below.
  3. Since current is the same in each resistor of a series circuit, you can quickly determine the values of I1, I2 and I3.
  4. Use the current and the resistance of each resistor to determine the voltage drop across each individual resistor. See second Physics Rules section below.
  5. As a final check, the sum of the voltage drops across each individual resistance should equal the battery voltage. While this check is not necessary, it is a wise habit to perform it in order to quickly catch any errors.

 


For series circuits, the mathematical formula for computing the equivalent resistance (Req) from the resistance values of the individual resistors (R1, R2, R3, ...) is

Req = R1 + R2 + R3 + ...

 


Current in a Series Circuit:

The overall current in a series circuit is no different than the current in an individual resistor. That is, the current through the battery is the same as the current in resistor 1 or resistor 2 or resistor 3 or ... . Since there are no branching locations, current is never divided and is everywhere the same. The amount of current is related to the voltage (Vtot) impressed across the circuit by the battery and the overall equivalent resistance (Req). In equation form, these ideas can be written as
Itot = I1 = I2 = I3 = Vtot / Req

Voltage Drops in a Series Circuit:

Charge gains energy (and electric potential) in the battery and loses energy (and electric potential) in the external circuit. The amount of electric potential gain in the battery is equal to the amount of loss in the external circuit. For series circuits, this loss occurs in a stepwise fashion as the charge passes through each resistor. The sum of the voltage drops across each resistor is equal to the voltage rating of the battery. The voltage drop across an individual resistor within a series circuit can be determined from the resistance of the resistor and the current through the circuit. For example:
V1 = I • R1V2 = I • R2V3 = I • R3

What is an effective method of mathematically analyzing a series circuit?

 

 

Three resistors are connected in series. If placed in a circuit with a 30-Volt power supply. Determine the equivalent resistance, the total circuit current, and the voltage drop across and current through each resistor. Enter your answers to the third decimal place.


Often times, success in physics demands that you have the proper approach - a good game plan. The following strategy should serve you well:

  1. Determine the equivalent resistance of the entire circuit. See Formula Fix section below.
  2. Determine the current in the battery using the equivalent resistance and the battery voltage. See first Physics Rules section below.
  3. Since current is the same in each resistor of a series circuit, you can quickly determine the values of I1, I2 and I3.
  4. Use the current and the resistance of each resistor to determine the voltage drop across each individual resistor. See second Physics Rules section below.
  5. As a final check, the sum of the voltage drops across each individual resistance should equal the battery voltage. While this check is not necessary, it is a wise habit to perform it in order to quickly catch any errors.

 


For series circuits, the mathematical formula for computing the equivalent resistance (Req) from the resistance values of the individual resistors (R1, R2, R3, ...) is

Req = R1 + R2 + R3 + ...


Current in a Series Circuit:

The overall current in a series circuit is no different than the current in an individual resistor. That is, the current through the battery is the same as the current in resistor 1 or resistor 2 or resistor 3 or ... . Since there are no branching locations, current is never divided and is everywhere the same. The amount of current is related to the voltage (Vtot) impressed across the circuit by the battery and the overall equivalent resistance (Req). In equation form, these ideas can be written as
Itot = I1 = I2 = I3 = Vtot / Req

Voltage Drops in a Series Circuit:

Charge gains energy (and electric potential) in the battery and loses energy (and electric potential) in the external circuit. The amount of electric potential gain in the battery is equal to the amount of loss in the external circuit. For series circuits, this loss occurs in a stepwise fashion as the charge passes through each resistor. The sum of the voltage drops across each resistor is equal to the voltage rating of the battery. The voltage drop across an individual resistor within a series circuit can be determined from the resistance of the resistor and the current through the circuit. For example:
V1 = I • R1V2 = I • R2V3 = I • R3

What is an effective method of mathematically analyzing a series circuit?