ISCET DC Circuits Fundamentals 4 — Questions and Answers
Question 1: A wire carries 5A of current. How many coulombs of charge pass a point in 30 seconds?
- 150 C (Correct answer)
- 6 C
- 35 C
- 0.17 C
Correct answer: 150 C
Q = I × t = 5A × 30s = 150 coulombs.
Question 2: Which statement correctly describes the relationship between EMF and terminal voltage of a battery under load?
- Terminal voltage is less than EMF due to internal resistance drop (Correct answer)
- Terminal voltage equals EMF regardless of load
- Terminal voltage is greater than EMF under load
- EMF decreases as load increases
Correct answer: Terminal voltage is less than EMF due to internal resistance drop
Under load, current through internal resistance causes a voltage drop, making terminal voltage = EMF − I×r.
Question 3: Two 60Ω resistors connected in series are then placed in parallel with a 40Ω resistor. What is the total resistance?
- 30Ω (Correct answer)
- 40Ω
- 160Ω
- 20Ω
Correct answer: 30Ω
Series pair = 60+60 = 120Ω; parallel with 40Ω gives Req = (120×40)/(120+40) = 4800/160 = 30Ω.
Question 4: What does the term 'short circuit' mean in a DC circuit?
- A path of near-zero resistance bypassing the load (Correct answer)
- An open path with infinite resistance
- A resistor with maximum rated value
- A circuit with only one component
Correct answer: A path of near-zero resistance bypassing the load
A short circuit is an unintended low-resistance connection that allows excessive current to bypass the intended load.
Question 5: Resistivity of a conductor depends on which factors?
- Material type and temperature (Correct answer)
- Length and cross-sectional area only
- Applied voltage
- Current density alone
Correct answer: Material type and temperature
Resistivity (ρ) is an intrinsic property of the material that changes with temperature, not with the physical dimensions of the conductor.
Question 6: A 1kΩ and 3kΩ resistor are connected in series across a 20V supply. What is the power dissipated by the 3kΩ resistor?
- 75 mW (Correct answer)
- 25 mW
- 100 mW
- 300 mW
Correct answer: 75 mW
I = 20V/4kΩ = 5mA; P = I²R = (0.005)² × 3000 = 0.000025 × 3000 = 0.075W = 75mW.
Question 7: Which instrument is used to measure current and must be connected in series with the circuit?
- Ammeter (Correct answer)
- Voltmeter
- Ohmmeter
- Wattmeter
Correct answer: Ammeter
An ammeter measures current and must be inserted in series so all circuit current flows through it; it has very low internal resistance.
ISCET DC Circuits Fundamentals 4
A wire carries 5A of current.
How many coulombs of charge pass a point in 30 seconds?