Acircuit contains two resistors connected in parallel. the value of r1 is 30 and the value of r2 is 60 . the supply of voltage is 24 vdc. what is the voltage drop across r2? a. 16 v b. 12 v c. 24 v d. 20 v

METHOD #1
R1 = 100 Ω
R2 = 400 Ω
R3 = 330 Ω
Re = equivalent resistance = to be determined

Equivalent Resistance (resistors in parallel)
1/Re = 1/R1 + 1/R2 + 1/R3 = 1/100 + 1/400 + 1/330 = 0.01 + 0.0025 + 0.00303
1/Re = 0.01553
Re = 1/0.01553 = 64.39 Ω

Ohm's Law
I = V/R

I = V/Re = 40 V / 64.39 Ω = 0.6212 AANSWER

METHOD #2
V1 = voltage across R1 = 40 V
V2 = voltage across R2 = 40 V
V3 = voltage across R3 = 40 V

Ohm's Law
I = V/R

I1 = V1/R1 = 40 V / 100 Ω = 0.4000 A
I2 = V2/R2 = 40 V / 400 Ω = 0.1000 A
I3 = V3/R3 = 40 V / 330 Ω = 0.1212 A

Circuit Current
Itotal = I1 + I2 + I3 = 0.4000 A + 0.1000 A + 0.1212 A = 0.6121 AANSWER 

2. A circuit contains three resistors connected in series. The value of R1 is 200 ohms, the 
value of R2 is 640 ohms, and the value of R3 is 500 ohms. The circuit is supplied with 6 VDC. 
What is the total voltage drop across the three resistors? 

R1 = 200 Ω
R2 = 640 Ω
R3 = 500 Ω
Re = equivalent resistance = to be determined

Equivalent Resistance (resistors in series)
Re = R1 + R2 + R3 = 200 Ω + 640 Ω + 500 Ω = 1,340 Ω

Ohm's Law
I = V/R

Itotal = V/Re = 6 V / 1,340 Ω
Itotal = 0.0045 A

V1 = Itotal x R1 = 0.0045 A x 200 Ω = 0.90 VVoltage Drop Across R1
V2 = Itotal x R2 = 0.0045 A x 640 Ω = 2.88 VVoltage Drop Across R2
V3 = Itotal x R3 = 0.0045 A x 500 Ω = 2.25 VVoltage Drop Across R3
Total Voltage Drop = 6.03 V ≈ 6VTotal Voltage Drop

3. A circuit contains two resistors connected in parallel. The value of R1 is 30 ohms and 
the value of R2 is 60 ohms. The supply of voltage is 24 VDC. What is the voltage drop 
across R2?

V = V1 = V2 = 24 VDC

Since the above equation is true for voltages of resistors in parallel,
then V2, the voltage drop across R2, is 24 VDC.ANSWER 

4. A circuit contains two 2,000-ohm resistors connected in parallel. What is the total 
resistance of the circuit?

METHOD #1
1/Re = 1/2,000 + 1/2,000 = 0.0005 + 0.0005
1/Re = 0.001
Re = 1/0.001 = 1,000 ΩANSWER

NOTE: Re = Rtotal

METHOD #2
Rtotal = (R1 x R2)/(R1 + R2) = (2,000 x 2,000)/(2,000 + 2,000) = 4,000,000/4,000
Rtotal = 1,000 ΩANSWER

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