309A Circuit Theory and Calculations 5

Question 1

What happens to current flow when the resistance in a circuit is doubled while voltage remains constant?

Accepted Answer

Current is halved

Answer

According to Ohm's Law (I = V/R), if resistance doubles and voltage stays constant, current is reduced by half. Current and resistance are inversely proportional.

Question 2

A 50 m run of No. 12 AWG copper conductor (resistance 5.21 Ω/km) carries 16 A. What is the voltage drop for the round trip?

Accepted Answer

8.34 V

Answer

Total length (round trip) = 100 m = 0.1 km. Total resistance = 5.21 × 0.1 = 0.521 Ω. Voltage drop = I × R = 16 × 0.521 = 8.34 V.

Question 3

What unit is used to measure electrical energy consumption?

Accepted Answer

Kilowatt-hour (kWh)

Answer

The kilowatt-hour (kWh) is the standard unit for measuring electrical energy consumption. It represents 1000 watts of power used for one hour.

Question 4

In a balanced three-phase wye system with a line voltage of 208 V, what is the phase voltage?

Accepted Answer

120 V

Answer

Phase voltage = Line voltage / √3 = 208 / 1.732 = 120 V. This is why 208/120 V three-phase systems provide 120 V for single-phase loads.

Question 5

What is the maximum demand of a load that operates at 50% duty cycle with a peak demand of 20 kW?

Accepted Answer

10 kW

Answer

Maximum demand with duty cycle = Peak demand × Duty cycle = 20 kW × 0.50 = 10 kW. The 50% duty cycle means the load operates half the time.

Red Seal Electrician 309A Practice Test

Red Seal Electrician 309A Practice Test

309A Circuit Theory and Calculations 5