ISCET DC Circuits Fundamentals Questions and Answers — Questions and Answers
Question 1: A technician measures a DC circuit with a 12V source and a single 100-ohm resistor. According to Ohm's Law, what is the expected current flowing through the circuit?
- 1.2 A
- 120 mA (Correct answer)
- 8.33 mA
- 12 A
Correct answer: 120 mA
Ohm's Law states that Current (I) = Voltage (V) / Resistance (R). In this circuit, I = 12V / 100Ω = 0.12A. To convert amperes to milliamperes (mA), multiply by 1000. Therefore, 0.12A * 1000 = 120 mA.
Question 2: In a DC series circuit containing three resistors (R1=10Ω, R2=20Ω, R3=30Ω), what is the total resistance (Rt)?
- 5.45 Ω
- 20 Ω
- 60 Ω (Correct answer)
- 600 Ω
Correct answer: 60 Ω
For resistors connected in series, the total resistance is the sum of the individual resistances. Therefore, Rt = R1 + R2 + R3 = 10Ω + 20Ω + 30Ω = 60Ω.
Question 3: A resistor has the following color bands: Yellow, Violet, Orange, and Gold. What is the nominal resistance and tolerance of this component?
- 470 Ω ±10%
- 4.7 kΩ ±5%
- 47 kΩ ±5% (Correct answer)
- 47 kΩ ±10%
Correct answer: 47 kΩ ±5%
The resistor color code is read as follows: Yellow (4), Violet (7), Orange (multiplier of 1,000). This gives a nominal value of 47 x 1,000 = 47,000 ohms, or 47 kΩ. The fourth band, Gold, indicates a tolerance of ±5%.
Question 4: According to Kirchhoff's Voltage Law (KVL), which of the following statements is true for any closed loop in a DC circuit?
- The algebraic sum of the currents entering a node is zero.
- The total power dissipated is equal to the total power supplied.
- The algebraic sum of all voltage drops and rises is zero. (Correct answer)
- The equivalent resistance is the reciprocal of the sum of the reciprocals of individual resistances.
Correct answer: The algebraic sum of all voltage drops and rises is zero.
Kirchhoff's Voltage Law (KVL) is based on the conservation of energy and states that the algebraic sum of the potential differences (voltages) around any closed loop or mesh in a circuit must be equal to zero.
Question 5: A technician is troubleshooting a simple DC circuit with a lamp that fails to light up. A multimeter measurement across the power source shows the correct voltage. Which of the following is the MOST likely cause of the problem?
- A short circuit across the lamp.
- An open circuit in the wiring. (Correct answer)
- The resistance of the lamp is too high.
- The power supply voltage is too low.
Correct answer: An open circuit in the wiring.
Since the power supply is verified to be working correctly, the most probable fault is a break in the current path, which is an open circuit. An open circuit, such as a broken wire or a blown fuse, would prevent any current from flowing to the lamp. A short would likely trip a protective device, and the problem states the source voltage is correct.
Question 6: Which circuit analysis theorem simplifies a complex linear circuit into an equivalent circuit consisting of a single voltage source in series with a single resistor?
- Norton's Theorem
- Superposition Theorem
- Ohm's Law
- Thevenin's Theorem (Correct answer)
Correct answer: Thevenin's Theorem
Thevenin's Theorem states that any linear electrical network can be replaced at two terminals by an equivalent circuit consisting of a voltage source (Vth) in series with a resistor (Rth).
ISCET DC Circuits Fundamentals Questions and Answers
A technician measures a DC circuit with a 12V source and a single 100-ohm resistor.
According to Ohm's Law, what is the expected current flowing through the circuit?