EIAT Basic Electrical Principles 5 — Questions and Answers
Question 1: What is the effect of increasing temperature on the resistance of most metallic conductors?
- Resistance decreases
- Resistance stays the same
- Resistance increases (Correct answer)
- Resistance becomes zero
Correct answer: Resistance increases
In most metals, higher temperatures cause increased atomic vibration, which impedes electron flow and raises resistance.
Question 2: In a parallel circuit with two branches carrying 4A and 6A respectively, what is the total current from the source?
- 2 A
- 4 A
- 6 A
- 10 A (Correct answer)
Correct answer: 10 A
In a parallel circuit, total current equals the sum of branch currents: 4 + 6 = 10 A.
Question 3: What is 'apparent power' in an AC circuit measured in?
- Watts (W)
- Volt-amperes (VA) (Correct answer)
- Vars (VAR)
- Joules (J)
Correct answer: Volt-amperes (VA)
Apparent power is the product of RMS voltage and RMS current in an AC circuit, expressed in volt-amperes (VA).
Question 4: Which type of motor is most commonly used in elevator traction drives?
- DC series motor
- AC induction motor (Correct answer)
- Universal motor
- Stepper motor
Correct answer: AC induction motor
AC induction motors are widely used in elevator traction drives due to their reliability, low maintenance, and efficiency with variable frequency drives.
Question 5: What does a voltmeter measure and how should it be connected in a circuit?
- Current; connected in series
- Voltage; connected in parallel (Correct answer)
- Resistance; connected in series
- Power; connected in series
Correct answer: Voltage; connected in parallel
A voltmeter measures the potential difference (voltage) between two points and must be connected in parallel across those points.
Question 6: What is the purpose of a contactor in elevator electrical systems?
- To convert AC to DC for the control circuit
- To measure current flow in the motor
- To switch high-current motor circuits using a low-current control signal (Correct answer)
- To regulate voltage to the motor drive
Correct answer: To switch high-current motor circuits using a low-current control signal
A contactor is an electrically operated switch that uses a small control current to open or close a high-current circuit, such as a motor power circuit.
Question 7: What is the correct color code for the ground wire in US electrical installations?
- White or gray
- Black
- Red
- Green or bare copper (Correct answer)
Correct answer: Green or bare copper
In US wiring, the equipment grounding conductor is identified by green insulation, green with a yellow stripe, or bare copper.
EIAT Basic Electrical Principles 5
What is the effect of increasing temperature on the resistance of most metallic conductors?