OAR OAR Mechanical Comprehension: Electricity 3 — Questions and Answers
Question 1: In a series circuit with a 12V source and three equal 4Ω resistors, what is the voltage drop across each resistor?
- 12V
- 4V (Correct answer)
- 3V
- 1V
Correct answer: 4V
Total resistance is 12Ω, current is 1A, and voltage drop across each 4Ω resistor is 1A × 4Ω = 4V.
Question 2: What is the purpose of a fuse in an electrical circuit?
- Increase voltage
- Store electrical energy
- Protect against excessive current (Correct answer)
- Reduce resistance
Correct answer: Protect against excessive current
A fuse contains a wire that melts and breaks the circuit when current exceeds a safe level, preventing damage.
Question 3: Two identical 10Ω resistors are connected in parallel. What is the combined resistance?
- 20Ω
- 10Ω
- 5Ω (Correct answer)
- 2.5Ω
Correct answer: 5Ω
Two identical resistors in parallel produce half the resistance of one: 10/2 = 5Ω.
Question 4: What unit measures electrical charge?
- Ampere
- Volt
- Coulomb (Correct answer)
- Watt
Correct answer: Coulomb
The coulomb (C) is the SI unit of electric charge; one ampere equals one coulomb per second.
Question 5: A transformer has 200 primary turns and 50 secondary turns. If the primary voltage is 120V, what is the secondary voltage?
- 480V
- 60V
- 30V (Correct answer)
- 15V
Correct answer: 30V
Voltage ratio equals turns ratio: V_s = 120 × (50/200) = 120 × 0.25 = 30V.
Question 6: What type of electricity is produced by a battery?
- Alternating current (AC)
- Direct current (DC) (Correct answer)
- Static electricity
- Pulsed AC
Correct answer: Direct current (DC)
Batteries produce direct current (DC) because current flows consistently in one direction due to chemical reactions.
Question 7: Which component opposes changes in current in an AC circuit?
- Resistor
- Capacitor
- Inductor (Correct answer)
- Diode
Correct answer: Inductor
An inductor stores energy in a magnetic field and opposes changes in current through electromagnetic induction.
OAR OAR Mechanical Comprehension: Electricity 3
In a series circuit with a 12V source and three equal 4Ω resistors, what is the voltage drop across each resistor?