Part Seven - Circuits

Question 1

What does an ammeter measure?

Answer 1

Flow of current through a component or circuit. (Amps)

Question 2

What does a voltmeter measure?

Answer 2

The voltage drop over a component. (Volts)

Question 3

What is the rule concerning current in a series circuit?

Answer 3

The same magnitude of current passes through each part of a series circuit

Question 4

What is the rule concerning voltage in a series circuit?

Answer 4

The total voltage equals the sum of all voltage drops of all components in a series circuit.

Question 5

What is the rule concerning resistance in a series circuit?

Answer 5

The resistance is equal to the sum of all resistances in a series circuit. R(total) = R1 + R2+ R3 + …

Question 6

What is the rule concerning power in a series circuit?

Answer 6

The total power is the sum of the power of each resistor/component, in a series circuit.

Question 7

What is the rule concerning resistance in a parallel circuit?

Answer 7

Total resistance is equal inverse sum of all resistances in a parallel circuit. 1/R(total) = 1/R1 + 1/R2 + 1/R3 + …

Question 8

What is the rule concerning current in a parallel circuit?

Answer 8

The sum of the currents through each path is equal to the total current in the parallel circuit.

Question 9

What is the rule concerning voltage in a parallel circuit?

Answer 9

The voltage is the same across each component of the parallel circuit.

Question 10

What is the rule concerning power in a parallel circuit?

Answer 10

The total power is the sum of the power of each resistor/component in a parallel circuit.

Question 11

In a series circuit with two resistors, question 55 on the review, R1=6Ω and R2=12Ω, and the voltage over R1 is 5 V, what is the current passing through R2?

Answer 11

I1 = V1/R1
I1 = 5V/6 ohms
I1 = 0.83 A
I1 = I2 = 0.83 A
REMEMBER - in series circuits the magnitude of current through each resistor/component is equal.

Question 12

In a series circuit with two resistors, question 55 on the review, R1=6Ω and R2=12Ω, and the voltage over R1 is 5 V, what is the voltage over R2?

Answer 12

V2 = (I2)(R2)
V2 = (0.83 A)(12 ohms)
V2 = 9.99 V

Question 13

In a parallel circuit, two resistors in parallel, question 56, R1=5Ω and R2=4Ω, and the current passing through R1 is 0.1 A, what is the voltage over R2?

Answer 13

V1 = (R1)(I1)
V1 = (5 ohms)(0.1 A)
V1 = 0.5 V
V1 = V2 = 0.5 V
REMEMBER - for parallel circuits, the voltage drop across resistors in parallel are equal.

Question 14

In a parallel circuit, two resistors in parallel, question 56, R1=5Ω and R2=4Ω, and the current passing through R1 is 0.1 A, what’s the current thru R2?

Answer 14

I2 = V2/R2
I2 = 0.5 V/4 ohms
I2 = 0.125 A

Question 15

What is the total/simplified resistance of the series circuit with a power source of 125 V and three resistors, R1 = 20 ohms, R2 = 30 ohms, R3 = 50 ohms, question 57?

Answer 15

R(total) = R1 + R2 + R3
R(total) = 20 ohms + 30 ohms + 50 ohms
R(total) = 100 ohms

Question 16

What is the total current of the series circuit with a power source of 125 V and three resistors, R1 = 20 ohms, R2 = 30 ohms, R3 = 50 ohms, question 57?

Answer 16

I(total) = V(total)/R(total)
I(total) = 125 V/100 ohm
I(total) = 1.25 A

Question 17

What is the current through each resistor in the series circuit where R1=20Ω, R2=30Ω and R3=50Ω and the total volts =125, question 57?

Answer 17

Because the resistors are in series, so the magnitude of the current through each resistor is equal/constant.

I(total) = I1 = I2 = I3
I1 & I2 & I3 = 1.25 A

Question 18

What is the voltage drop of each resistor in a series circuit in question 57, where R1=20Ω, R2=30Ω and R3=50Ω and the total volts =125?

Answer 18

V1 = (I1)(R1)
V1 = (1.25 A)(20 ohms)
V1 = 25 V

V2 = (I2)(R2)
V2 = (1.25 A)(30 ohms)
V2 = 37.5 V

V3 = (I3)(R3)
V3 = (1.25 A)(50 ohms)
V3 = 62.5 V

The voltage of each individual resistor added together should equal the voltage of the power supply - 27 V + 37.5 V + 62.5 V = 125 V

Question 19

What is the power “used” by each resistor in the series circuit from problem 57, where R1=20Ω, R2=30Ω and R3=50Ω and the total volts =125?

Answer 19

P1 = (V1)(I1)
P1 = (21 V)(1.25 A)
P1 = 26.25 W

P2 = (V2)(I2)
P2 = (37.5 V)(1.25 A)
P2 = 46.88 W

P3 = (V3)(I3)
P3 = (62.5 V)(1.25 A)
P3 = 78.13 W

Question 20

What is the total/simplified resistance of the parallel circuit from problem 58, where there are three parallel resistors, R1 = 20 ohms, R2 = 100 ohms, R3 = 50 ohms, and the power source has 125 V.

Answer 20

1/R(total) = 1/R1 + 1/R2 + 1/R3
1/R(total) = 1/20 ohms + 1/100 ohms + 1/50 ohms
1/R(total) = 5/100 ohms + 1/100 ohms + 2/100 ohms
1/R(total) = 8/100 ohms

NOW - you can solve for R(total) by multiplying R(total) to both sides and then dividing both sides by 8/100 - and to divide by a fraction you multiply the inverse.

So: 1 = 8/100 ohms (R(total))
(100/8)(1) = R(total)
R(total) = 12.5 ohms

OR - when you are at this stage: 1/R(total) = 8/100 ohms you know that the inverse is true, so you flip both and solve, getting the same result.

Question 21

What is the total current of the parallel circuit from problem 58, where there are three parallel resistors, R1 = 20 ohms, R2 = 100 ohms, R3 = 50 ohms, and the power source has 125 V.

Answer 21

I1 = (V1)/(R1)
I1 = (125 V)/(20 ohms)
I1 = 6.25 A

I2 = (V2)/(R2)
I2 = (125 V)/(100 ohms)
I2 = 1.25 A

I3 = (V3)/(R3)
I3 = (125 V)/(50 ohms)
I3 = 2.50 A

The current of each individual resistor added together should equal the total current of the circuit - 6.25 A + 1.25 A + 2.50 A = 10 A

Question 22

What is the total current of the parallel circuit from problem 58, where there are three parallel resistors, R1 = 20 ohms, R2 = 100 ohms, R3 = 50 ohms, and the power source has 125 V.

Answer 22

I(total) = (V1)/(R1)
I(total) = (125 V)/(12.5 ohms)
I(total) = 10 A

Question 23

What is the voltage drop of each resistor in the parallel circuit from problem 58, where there are three parallel resistors, R1 = 20 ohms, R2 = 100 ohms, R3 = 50 ohms, and the power source has 125 V.

Answer 23

Because the resistors are in parallel, the voltage drops of each parallel resistor is equal in magnitude.

V(total) = V1 = V2 = V3
V1 = 125 V
V2 = 125 V
V3 = 125 V

Question 24

What is the power “used” by each resistor in the parallel circuit from problem 58, where there are three parallel resistors, R1 = 20 ohms, R2 = 100 ohms, R3 = 50 ohms, and the power source has 125 V.

Answer 24

P1 = (V1)(I1)
P1 = (125 V)(6.25 A)
P1 = 781.25 W

P2 = (V2)(I2)
P2 = (125 V)(1.25 A)
P2 = 156.25 W

P3 = (V3)(I3)
P3 = (125 V)(2.50 A)
P3 = 312.50 W