309A Circuit Theory and Calculations

Question 1

What is the total resistance of three resistors connected in series with values of 10 Ω, 20 Ω, and 30 Ω?

Accepted Answer

60 Ω

Answer

In a series circuit, total resistance is the sum of all individual resistances: 10 + 20 + 30 = 60 Ω. Current flows through each resistor sequentially.

Question 2

A 240 V single-phase circuit supplies a 5 kW resistive load. What is the current draw?

Accepted Answer

20.83 A

Answer

Using P = V × I, we get I = P/V = 5000/240 = 20.83 A. For a purely resistive load, the power factor is 1, so no correction is needed.

Question 3

What is the power factor of a circuit with a real power of 8 kW and an apparent power of 10 kVA?

Accepted Answer

0.80

Answer

Power factor = Real Power / Apparent Power = 8 kW / 10 kVA = 0.80. This means 80% of the apparent power is doing useful work.

Question 4

In a parallel circuit with two resistors of 12 Ω and 6 Ω, what is the total resistance?

Accepted Answer

4 Ω

Answer

For parallel resistors: 1/Rt = 1/R1 + 1/R2 = 1/12 + 1/6 = 1/12 + 2/12 = 3/12, so Rt = 12/3 = 4 Ω.

Question 5

A conductor carries 15 A and has a resistance of 0.5 Ω. What is the voltage drop across it?

Accepted Answer

7.5 V

Answer

Using Ohm's Law: V = I × R = 15 A × 0.5 Ω = 7.5 V. This represents the voltage lost as heat in the conductor.

Red Seal Electrician 309A Practice Test

Red Seal Electrician 309A Practice Test

309A Circuit Theory and Calculations