DC Circuits Lab

George Washington University

DC Circuits LabProfessor Ahmadi ， Xin Xu

ECE 1020


OutlineDC and AC circuitOmh’s LawEquivalent resistance in series and parallel

cuicuitsExercises & Homework


Direct Current (DC) & Alternating Current (AC)DC: uni-directional movement of electric charges

AC: the direction of the movement of electric charges reverses periodically


Ohm’s Law

€

V = I × RQuantifying the relationship between voltage and

current

V voltage, volt (V)I current, amp (A)R resistance ohm (Ω) V R

I


An Example

3V = I x 1000 ΩSolve for I:

I=3V / 1000 Ω = 3milliAmps

3V R = 1K Ω

I = ? Amps

Determine the current using Ohm’s Law

€

V = I × R


Resisters in Series

V

R1 I

R2

R3

€

V1 = I1 × R1

V2 = I2 × R2

V3 = I3 × R3

€

I1 = I2 = I3 = I

Apply Ohm’s Law on each resister

Just one path, currents are equal

Voltage drops can be added up

€

Req = R1 + R2 + R3

€

V = I1R1 + I2R2 + I3R3 = I(R1 + R2 + R3)

Equivalent resistance


Principles for Resisters in Series

V

R1 I

R2

R3

€

Req = R1 + R2 + R3

Current remains same in one circleVoltage can be added upEquivalent Resistance equal to sum of all resisters

in series


ExamplesOnline examples for resistances

http://www.falstad.com/circuit/e-resistors.html


Resisters in Parallel

V R1

I

R2 R3

€

V1 = I1 × R1

V2 = I2 × R2

V3 = I3 × R3

€

V1 =V2 =V3 =V

Apply Ohm’s Law on each resister

Current is divided to 3 paths

Voltages are same on each path

€

Req =1

1R1

+1R2

+1R3

Equivalent resistance

€

I = I1 + I2 + I3 =V1

R1

+V2

R2

+V3

R3

=V × (1R1

+1R2

+1R3

) =V /(1

1R1

+1R2

+1R3

)


Principles for Resisters in ParallelVoltages remain same in parallel pathsCurrent can be added up

V R1

I

R2 R3

€

Req =1

1R1

+1R2

+1R3





Combined

€

Req =1/(1R2

+1R3

)

Find equivalent resistance for parallel resistances

V

R1

I

R2 R3

V

R1

I

Req

Solve the serial circuit

€

V = I × (R + Req )





Exercises


Exercises – Ohm’s LawGiven a circuit with a power source V = 9V,find the loop

current if the resistance is 100 Ohm

Find the loop current by hand, and then build the circuit using the online interactive simulator

What is the current if the resistance is doubledWhat is the current if the resistances is reduced by 50%What is the current if the voltage is doubled?What is the current if the voltage is reduced by 50%

€

V = 9V ,R1 =100Ω,I = ?


Exercises - seriesGiven a circuit with a power source V = 12V,find

the loop current if resistances are in series

Find the loop current by hand, and then build the circuit using the online interactive simulator

What is the loop current if all resistances are doubled

What is the loop current if all resistances are reduced by 50%

€

R1 = 300Ω,R2 =150Ω,R3 = 600Ω


Exercises - parallelGiven a circuit with a power source V = 12V,find

the loop current I if 2 resistances are connected in parallel

€

R1 =100Ω,R2 =100Ω

V=12V R1 R2

Find the current I by hand, and then build the circuit using the online interactive simulator

What is the current I if all resistances are doubled?

What is the current I if all resistances are reduced by 50%

I = ?


Exercises - parallelGiven a circuit with a power source V = 12V,find

the loop current if 3 resistances are connected in parallel

€

R1 =100Ω,R2 =100Ω,R3 =100Ω

V R1 R2 R3

Find the current I by hand, and then build the circuit using the online interactive simulator

What is the current I if all resistances are doubled

What is the current I if all resistances are reduced by 50%

I = ?


Exercises – series/parallelGiven a circuit with a power source V = 5V,find

the loop current I if R1, R2 are connected in parallel, and then connected to R3 in series

€

R1 =100Ω,R2 =100Ω,R3 = 50Ω

V

R3

R1 R2

Find the current I by handBuild the circuit using the

online interactive simulator to verify your results

I = ?


Exercises – series/parallelGiven a circuit with a power source V = 5V,find

the loop current if R1, R2, R3 are connected in parallel, and then connected to R4 in series

€

R1 = 300Ω,R2 = 300Ω,R3 = 300Ω,R4 =100Ω

V R1 R2 R3

R4

Find the loop current I by hand

Build the circuit using the online interactive simulator to verify your results

I = ?


Exercises – series/parallelFind the loop current I by hand, and then build the

circuit using the online interactive simulator

V

R1

I = ?

R2

R3 R4

€

V = 9VR1 = 200Ω,R2 = 50ΩR3 = 600Ω,R4 = 300Ω


HomeworkFind the loop current I, and voltage and current

for each resistor Build the circuit using the online interactive

simulator to verify your results

V

R1

R2

R3 R4

€

V = 9VR1 =100Ω,R2 =100ΩR3 = 200Ω,R4 = 400Ω

I = ? €

V1,I1;V2,I2;V3,I3;V4,I4

Documents

DC Circuits Lab