Mechanical Aptitude Basic Electrical Circuits Questions and Answers 2 — Questions and Answers
Question 1: In a parallel circuit with three resistors of 10Ω, 20Ω, and 30Ω, which resistor carries the most current?
- The 10Ω resistor (Correct answer)
- The 20Ω resistor
- The 30Ω resistor
- All carry equal current
Correct answer: The 10Ω resistor
In a parallel circuit, voltage across each branch is equal. By Ohm's law (I = V/R), the resistor with the lowest resistance draws the most current. The 10Ω resistor has the least resistance, so it carries the most current.
In parallel circuits, each branch shares the same voltage from the power source. According to Ohm's law, current is inversely proportional to resistance (I = V/R). With equal voltage across all branches, the branch with the smallest resistance will have the largest current flow. The 10Ω resistor allows more electrons to pass through per unit time compared to the 20Ω or 30Ω resistors.
Question 2: What happens to the total resistance in a circuit when you add another resistor in parallel?
- Total resistance increases
- Total resistance decreases (Correct answer)
- Total resistance stays the same
- Total resistance doubles
Correct answer: Total resistance decreases
Adding a resistor in parallel provides an additional path for current to flow, which always decreases the total resistance of the circuit. The total parallel resistance is always less than the smallest individual resistor.
When resistors are connected in parallel, the reciprocal of total resistance equals the sum of reciprocals of individual resistances (1/Rt = 1/R1 + 1/R2 + ...). Each additional parallel path gives current another route, effectively reducing overall opposition to current flow. This is why the total resistance of a parallel combination is always less than the smallest individual resistor in the group.
Question 3: A 12V battery is connected to a series circuit with two resistors. If the voltage drop across the first resistor is 8V, what is the voltage across the second resistor?
- 4V (Correct answer)
- 8V
- 12V
- 20V
Correct answer: 4V
In a series circuit, the total voltage equals the sum of voltage drops across all components (Kirchhoff's Voltage Law). Since the battery provides 12V and 8V drops across the first resistor, the remaining 4V must drop across the second resistor.
Kirchhoff's Voltage Law states that the algebraic sum of all voltage differences around any closed circuit loop must equal zero. In practical terms, the supply voltage (12V) is distributed among all series components. If one resistor accounts for 8V of the total 12V drop, then 12V - 8V = 4V remains for the second resistor. This principle is fundamental to voltage divider circuits used extensively in electronics.
Question 4: Which component in a circuit stores energy in an electric field?
- Resistor
- Inductor
- Capacitor (Correct answer)
- Transistor
Correct answer: Capacitor
A capacitor stores energy in an electric field between its plates. Resistors dissipate energy as heat, inductors store energy in a magnetic field, and transistors act as switches or amplifiers.
Capacitors consist of two conductive plates separated by a dielectric (insulating) material. When voltage is applied, charge accumulates on the plates, creating an electric field in the dielectric that stores energy. The energy stored equals ½CV², where C is capacitance and V is voltage. This distinguishes capacitors from inductors, which store energy in magnetic fields created by current flowing through coiled wire.
Question 5: What is the unit of electrical resistance?
- Ampere
- Volt
- Ohm (Correct answer)
- Watt
Correct answer: Ohm
The ohm (Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm. Amperes measure current, volts measure potential difference, and watts measure power.
The ohm (symbol Ω) is defined as the resistance between two points of a conductor when a constant potential difference of one volt applied between those points produces a current of one ampere. Georg Ohm discovered this relationship in 1827, which became known as Ohm's Law: V = IR. One ohm equals one volt per ampere (1 Ω = 1 V/A).
Question 6: In a circuit, what does a fuse protect against?
- Low voltage
- Excessive current (Correct answer)
- Static electricity
- Power surges only
Correct answer: Excessive current
A fuse is a safety device designed to protect circuits from excessive current (overcurrent). It contains a thin wire or strip that melts and breaks the circuit when current exceeds a safe level, preventing damage to components or fire hazards.
Fuses are the simplest form of overcurrent protection. They contain a calibrated metal element that heats up as current passes through it. When current exceeds the fuse's rated value, the element reaches its melting point and opens the circuit, stopping all current flow. This sacrificial action protects more expensive components and wiring from damage caused by short circuits, overloads, or equipment faults. Once blown, a fuse must be replaced, unlike circuit breakers which can be reset.
Mechanical Aptitude Basic Electrical Circuits Questions and Answers 2
In a parallel circuit with three resistors of 10Ω, 20Ω, and 30Ω, which resistor carries the most current?