AC/DC ELECTRICAL CIRCUIT

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SKILL 1 CALCULAT E SERIES RESIS TANCE GIVEN EACH LOAD'S

RESISTANCE

Procedure Overview

In this procedure, you will calculate total resistance in a series circuit and verify your calculations by measuring the total resistance.

□ 1. Calculate the total resistance of the circuit in figure 1-1.

RT= _____________________ _

12V

R1=10n R2 = 25n

Figure 1-1. Calculation of Total Resistance

Show all your work to calculate Total Resistance RT =

LB227-BD03UEN-E1 -S01, REV. B CIRCUIT ANALYSIS

R3 = 25n

(Ohms)

S01-1

SKILL 1 CALCULATE SERIES RESISTANCE GIVEN EACH LOAD'S RESISTANCE

□ 2. Connect the series circuit shown in figure 1-2.

This will allow you to prove that the resistances add together in series.

NOTE

You will not need to connect the power supply to take the measurements in this circuit.

R1 = 10Q R2 = 25Q R3 = 25Q

POINT A POINT B

Figure 1-2. Series Circuit

□ 3. Measure the resistance of each load.

Resistance RI = __________________ _

Resistance R2 = __________________ _

Resistance R3 = __________________ _

(Ohms)

□ 4. Measure the total resistance by placing one lead at point A and the other lead at point B.

Total resistance= ___________________ (Ohms)

There might be a slight variance.

□ 5. Disconnect the circuit and store all components.

LB227-BD03UEN-E1 -S01, REV. B CIRCUIT ANALYSIS

mclass

Typewritten Text

This step will be completed in the LAB.

SKILL 2 USE OHM'S LAW TO CALCULATE VOLTAGE, CURRENT, AND RESISTANCE IN A SERIES CIRCUIT

Procedure Overview

In this procedure, you will calculate voltage, current, and resistance in a series circuit by applying Ohm's Law.

□ l. Calculate the power supply's voltage for the circuit shown in figure 2-1 if the current is 2 amps and resistor Rl has a resistance of 20 ohms.

R 1

= 20 Q

Figure 2-1. Voltage Calculation

Voltage (E) = ___________________ (Volts)

The solution to this problem is found by using Ohm's law

LB227-BD03UEN-E1 -S02, REV. B CIRCUIT ANALYSIS

SKILL 2 USE OHM'S LAW TO CALCULAT E VOLTAGE, CURRENT, AND RESISTANCE IN A SERIES CIRCUIT

□ 4. Calculate the current in the circuit shown in figure 2-3. The power supply is

a constant voltage power supply.

Current (I)= __________________ (Amps)

24 V +

100

Figure 2-3. Current Calculation

Being able to calculate current in a circuit is important if you want to add a circuit protection device. You must know the total current in order to select

the properly-rated protection device. If the current is much above the device's

rating, the device will blow or trip when operated in the circuit, as you will

see later in this LAP.

□ 5. Calculate the current in the circuit shown in figure 2-4 using the voltage and

resistance values.

Current=

24V +

30 90

Figure 2-4. Current Calculation

LB227-BD03UEN-E1 -S02, REV. B CIRCUIT ANALYSIS

(Amps)

S02-3

SKILL 2 USE OHM'S LAW TO CALCULATE VOLTAGE, CURRENT, AND RESISTANCE IN A SERIES CIRCUIT

□ 6. Calculate the resistance of the load in figure 2-5 if the voltage applied to the circuit is 120V and the current is 3A.

R= _______________________ _ (Ohms)

120V

I= 3A

Figure 2-5. Resistance Calculation

Knowing the resistance of a load is important in designing a circuit because of the effect it has on the current and voltage. Sometimes loads do not specify their resistance. However, Ohm's Law gives us a means of determining an unknown resistance value.

□ 7. Calculate the resistance of the load shown in figure 2-6. The voltage and current are shown.

Resistance= _____________________ (Ohms)

r;1.2A

Figure 2-6. Resistance Calculation

LB227-BD03UEN-E1 -S02, REV. B CIRCUIT ANALYSIS

12V

S02-4

SKILL 2 USE OHM'S LAW TO CALCULATE VOLTAGE, CURRENT, AND RESISTANCE IN A SERIES CIRCUIT

□ 8. Calculate the current in the circuit shown in figure 2-7.

Current= _____________________ _ (Amps)

35V

12n

5£2 20£2 7£2

Figure 2-7. Current Calculation

□ 9. Calculate the unknown resistance value in the circuit shown in figure 2-8.

HINT

You will need to determine the voltage drop across both resistors.

Resistance= ____________________ _

I= .8A

Figure 2-8. Resistance Calculation

LB227-BD03UEN-E1 -S02, REV. B CIRCUIT ANALYSIS

24V

(Ohms)

S02-5

SKILL 3 CALCULATE THE TOTAL POWER USED BY A SERIES CIRCUIT

Procedure Overview

In this procedure, you will calculate the total power used in a series circuit.

This is a common calculation designed to determine the sizes of components

needed in the circuit.

□ 1. Calculate the total power used in the circuit shown in figure 3-1.

PT= ______________________ (Watts)

The solution is found as follows:

Since we know the total voltage and current, we can use the first power in

series formula.

PT = IT X ET

11 = .19A 24V

Figure 3-1. Total Power Calculation

R, = 420

LB227-BD03UEN-E1 -S03, REV B CIRCUIT ANALYSIS

SKILL 3 CALCULATE THE TOTAL POWER USED BY A SERIES CIRCUIT

□ 2. Calculate the power used by the circuit shown in figure 3-2.

p = ______________________ (Watts)

Since the current and resistance are given, we can use what formula P=_____

p =

I =2A

Figure 3-2. Total Power Calculation

□ 3. Calculate the power used by the circuit shown in figure 3-3.

P = ____________________ (Watts)

I =2A

Figure 3-3. Total Power Calculation

LB227-BD03UEN-E1 -S03, REV. B CIRCUIT ANALYSIS

24V

S03-2

SKILL 3 CALCULATE THE TOTAL POWER USED BY A SERIES CIRCUIT

□ 4. Calculate the power used by the circuit shown in figure 3-4.

PT= ______________________ (Watts)

1=3A

Figure 3-4. Total Power Calculation

100

□ 5. Calculate the power used by the circuit shown in figure 3-5 using the total

resistance.

PT= _______________________ (Watts)

I= 2A

R, =2Q

Figure 3-5. Total Power Calculation

LB227-BD03UEN-E1 -S03, REV. B CIRCUIT ANALYSIS

R 2

= 4 0

S03-3

SKILL 3 CALCULATE THE TOTAL POWER USE D BY A SERIES CIRCUIT

□ 6. Perform the following substeps to calculate the total power used in the

circuit shown in figure 3-5 by calculating the individual power used by each

component.

Figure 3-5 shows a circuit with the current and each resistance given. The

source voltage is not known.

A. Calculate the power dissipation of RI.

PR 1 = _____________________ (Watts)

B. Repeat substep A for R 2

PR2 = ______________________ (Watts)

C. Calculate the total power dissipation by adding the individual power

dissipations.

PT = ______________________ (Watts)

The total power used is ___ watts. This should be the same as you

calculated in step 5.

□ 7. Calculate the total power used by the circuit shown in figure 3-6.

PT= ______________________ (Watts)

J 1 = 1.5A

R, = 47Q

Figure 3-6. Total Power Calculation

LB227-BD03UEN-E1 -S03, REV. B CIRCUIT ANALYSIS

SKILL 4 CALCULATE THE MAIN LINE CURRENT IN

A PARALLEL CIRCUIT

Procedure Overview

In this procedure , you will calculate the total current in a parallel circuit using Kirchhoff's current law. You will then connect a circuit and measure the current in each branch to verify your calculations .

□ 1. Use Ohm's Law to calculate the current in each branch of the circuit in figure 4-1.

Current 1 1 = ____________________ (Amps)

Current 1 2 = ____________________ (Amps)

Current 1 3 = ___________________ (Amps)

12V

Figure 4-1. Main Line Current Calculation

□ 2. Calculate the main line current using the branch currents you calculated in step l and Kirchhoff's Current Law.

lr = 1 1

+1 2

+1 3

Main line current= _________________ (Amps)

LB227-BD03UEN-E1 -S04, REV. B CIRCUIT ANALYSIS

- - - -- -- - --- --------------

SKILL 5 CALCULATE THE TOTAL PARALLEL RESISTANCE

Procedure Overview

In this procedure, you will calculate the total resistance of the circuit using the parallel resistance formula. In the first step you will be given an example.

□ 1. Calculate the total resistance of the circuit in figure 5-1.

� = ___________________ (Ohms)

1 R =----r

1 1 1 -+-+ R

, R R

�=0.24A

+ 12V R= 1

150D

Figure 5-1. Total Resistance Calculation

R= 2

300D R=

100n

S05-1

SKILL 5 CALCULAT E THE TOTAL PARALLEL RESISTANCE

NOTE

Each time another load is added to a parallel circuit, the effective resistance

is lowered. This is exactly the opposite effect of adding a load to a series circuit,

which would increase the effective resistance of that circuit.

This is the reason the main line current increases as more branches are

added. Since the total resistance is reduced, Ohm's Law says that the current

must increase since the voltage is constant.

□ 2. Calculate the total resistance of the parallel circuit shown in figure 5-2.

(Ohms)

12V

Figure 5-2. Total Resistance Calculation

LB227-BD03UEN-E1 -SOS, REV. B CIRCUI T ANALYSIS

SKILL 5 CALCULATE THE TOTAL PARALLEL RESISTANCE

□ 3. Now connect the circuit shown in figure 5-2.

Do not connect the circuit to the power supply.

Any time you make resistance measurements m a circuit, you should disconnect the circuit from the power supply.

□ 4. Measure the resistance of each branch of the circuit with the DMM. Remember to disconnect one side of the load in that branch from the circuit before measuring. Reconnect each load after you make your measurement.

R = I

R = 2

___________________ (Ohms)

R1 = ------------------- (Ohms)

□ 5. Measure the total resistance of the circuit, as shown in figure 5-3.

Total resistance= ___________________ (Ohms)

DISCONNECTED SUPPLY Q

Figure 5-3. Total Resistance Measurement

□ 6. Disconnect the circuit and store all components.

LB227-BD03UEN-E1 -S05, REV. B CIRCUIT ANALYSIS

SKILL 6 CALCULATE THE TOTAL POWER USED

IN A PARALLEL CIRCUIT

Procedure Overview

In this procedure, you will calculate the total power used in a circuit. This calculation uses the same principles used to calculate the power in a series circuit except that the calculation of total resistance is different.

In steps I and 2 you will be given some examples. Then you will do it yourself.

□ 1. Calculate the total power used in the circuit shown in figure 6- 1.

The power in a parallel circuit can be calculated using any of the three methods used for series circuits: • Method A - Calculate total resistance of the parallel circuit and use the FR

formula. • Method B - Determine the total voltage and current and use the I x E

formula • Method C - Calculate the power consumed by each component and add

them together, as follows:

p T = pl + p2 + p3 + ' ' .

I= 3AMPS

E =24V R = 1

Figure 6-1. Total Power Used by a Parallel Circuit

R = 2 R = 3

PT= ______________________ (Watts)

Since the circuit in figure 33 shows the total voltage and current, method B (I x E) can be used as follows:

Pr = IrxEr Pr =

LB227-BD03UEN-E1 -S06, REV. B CIRCUIT ANALYSIS

SKILL 6 CALCULATE THE TOTAL POWER USED IN A PARALLEL CIRCUIT

□ 2. Perform the following substeps to calculate the total power used in the circuit shown in figure 6-2.

I= 2A

Figure 6-2. Total Power Calculation

R 1 = 10D

A. Calculate the total resistance, �-

1 R =--

T 1 1 -+

R R 1 2

�= _____________________ Ohms

B. Calculate the total power.

P T

= I2 X Rr

P = ______________________ (Watts) T

LB227-BD03UEN-E1 -S06, REV. B CIRCUIT ANALYSIS

SKILL 6 CALCULATE THE TOTAL POWER USED IN A PARALLEL CIRCUIT

□ 3. Perform the following substeps to calculate the total power used in the circuit shown in figure 6-3. Use method C to solve it.

20V

MAXIMUM

POWER

=80W

R = 1

500

Figure 6-3. Total Power Calculation

R = 2

20 n

R = 3

1 on

Calculate the current in each branch of the circuit.

IR 1 = ______________________ (Amps)

IR2 = ______________________ (Amps)

I = _____________________ (Amps) R

B. Now calculate the power dissipation of each load using the basic power formula (P = Ix E).

p = I

p = 2

p = 3

(Watts)

Since this is a parallel circuit, the voltage across each branch is equal to the source voltage.

C. Calculate the total power used by the circuit.

PT = ----------------------�

LB227-BD03UEN-E1 -S06, REV B CIRCUIT ANALYSIS

(Watts)

S06-3

SKILL 6 CALCULATE THE TOTAL P OWER USED IN A PARALLEL CIRCUIT

□ 4. Calculate the power used by the circuit shown in figure 6-4.

V= 24V

Figure 6-4. Total Power Calculation

10W 25W

PT= ______________________ (Watts)

□ 5. Calculate the power used by the circuit shown in figure 6-5.

I =2A

Figure 6-5. Total Power Calculation

100

300

150

PT= ______________________ (Watts)

o 6. Solve the following design problem.

Determine how many 1 00W light bulbs can be connected to a common

commercial building's circuit if the source voltage is l 20 VAC and the

maximum current that can be provided is 20A.

HINT: What is the maximum output power that the source can provide with

the 20A limit?

LB227-BD03UEN-E1 -S06, REV. B CIRCUIT ANALYSIS

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