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Chapter 2 Quiz — Ohm's Law and Basic Circuit Configurations

Multiple Choice Quiz

1. Ohm's Law states that, for a resistor with constant resistance:

  • [ ] A) Voltage and current are inversely proportional
  • [ ] B) Voltage and current are directly proportional
  • [ ] C) Resistance increases with temperature
  • [ ] D) Power is constant regardless of current
Answer

B) Voltage and current are directly proportional. Ohm's Law is \(V = IR\). When resistance \(R\) is constant, doubling the voltage doubles the current — a linear (directly proportional) relationship. This linearity is one of the most useful properties of resistive circuits.

2. A 15V source is connected to a 5kΩ resistor. The current through the resistor is:

  • [ ] A) 75 mA
  • [ ] B) 3 mA
  • [ ] C) 0.33 mA
  • [ ] D) 300 mA
Answer

B) 3 mA. Using Ohm's Law: \(I = V/R = 15\text{ V} / 5000\text{ Ω} = 0.003\text{ A} = 3\text{ mA}\).

3. Two resistors R1 = 4Ω and R2 = 6Ω are connected in series. Their equivalent resistance is:

  • [ ] A) 2.4 Ω
  • [ ] B) 5 Ω
  • [ ] C) 10 Ω
  • [ ] D) 24 Ω
Answer

C) 10 Ω. Series resistances add directly: \(R_{eq} = R_1 + R_2 = 4 + 6 = 10\text{ Ω}\). The equivalent resistance of a series combination is always larger than any individual resistor.

4. Two resistors R1 = 4Ω and R2 = 6Ω are connected in parallel. Their equivalent resistance is:

  • [ ] A) 2.4 Ω
  • [ ] B) 5 Ω
  • [ ] C) 10 Ω
  • [ ] D) 24 Ω
Answer

A) 2.4 Ω. Using the product-over-sum formula: \(R_{eq} = (R_1 \cdot R_2)/(R_1 + R_2) = (4 \times 6)/(4 + 6) = 24/10 = 2.4\text{ Ω}\). The equivalent resistance of a parallel combination is always less than the smallest individual resistor.

5. In a series circuit with a 12V source and three equal resistors, the voltage across each resistor is:

  • [ ] A) 36 V
  • [ ] B) 12 V
  • [ ] C) 6 V
  • [ ] D) 4 V
Answer

D) 4 V. In a series circuit, the source voltage divides among the resistors in proportion to their resistance. With three equal resistors, each gets \(12\text{V} / 3 = 4\text{V}\). The sum \(4 + 4 + 4 = 12\text{ V}\) satisfies Kirchhoff's Voltage Law.

6. A voltage divider uses R1 = 8kΩ and R2 = 2kΩ connected to a 10V source. The output voltage (across R2) is:

  • [ ] A) 8 V
  • [ ] B) 5 V
  • [ ] C) 2 V
  • [ ] D) 4 V
Answer

C) 2 V. Using the voltage divider formula:

\[V_{out} = V_{in} \times \frac{R_2}{R_1 + R_2} = 10 \times \frac{2\text{k}}{8\text{k} + 2\text{k}} = 10 \times \frac{2}{10} = 2\text{ V}\]

7. In a parallel circuit with a 24V source and two resistors (R1 = 6Ω, R2 = 12Ω), the current through R1 is:

  • [ ] A) 2 A
  • [ ] B) 4 A
  • [ ] C) 6 A
  • [ ] D) 3 A
Answer

B) 4 A. In a parallel circuit, the same voltage (24V) appears across both resistors. Each branch is analyzed with Ohm's Law independently: \(I_1 = V/R_1 = 24/6 = 4\text{ A}\).

8. A resistor has color bands: Orange, Orange, Red, Gold. Its resistance value and tolerance are:

  • [ ] A) 3.3kΩ ±5%
  • [ ] B) 3.3kΩ ±10%
  • [ ] C) 33kΩ ±5%
  • [ ] D) 330Ω ±5%
Answer

A) 3.3kΩ ±5%. Decoding: Orange = 3 (first digit), Orange = 3 (second digit), Red = ×100 (multiplier), Gold = ±5% (tolerance). Value = 33 × 100 = 3300Ω = 3.3kΩ, tolerance ±5%.

9. A resistor is rated at 1W. If 50V appears across it, what minimum resistance is required to stay within the power rating?

  • [ ] A) 500 Ω
  • [ ] B) 1000 Ω
  • [ ] C) 2500 Ω
  • [ ] D) 50 Ω
Answer

C) 2500 Ω. Using \(P = V^2/R\), solving for \(R\):

\[R_{min} = \frac{V^2}{P_{max}} = \frac{(50)^2}{1} = 2500\text{ Ω}\]

A resistance below 2500Ω would cause the power dissipation to exceed 1W, violating the rating.

10. The current divider rule states that, for two parallel resistors R1 and R2 with total current I, the current through R1 is:

  • [ ] A) \(I \times R_1 / (R_1 + R_2)\)
  • [ ] B) \(I \times R_2 / (R_1 + R_2)\)
  • [ ] C) \(I \times (R_1 + R_2) / R_2\)
  • [ ] D) \(I / R_1\)
Answer

B) \(I \times R_2 / (R_1 + R_2)\). The counterintuitive aspect: the current through R1 depends on R2. More current flows through the smaller resistance — the path of least resistance. The formula assigns more current to whichever branch has lower resistance.