General G5C: Transformers and combining parts
These are the 14 official questions in group G5C of the 2023–2027 General question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
- G5C01Question 1
What causes a voltage to appear across the secondary winding of a transformer when an AC voltage source is connected across its primary winding?
- ACapacitive coupling
- BDisplacement current coupling
- CMutual inductance Correct
- DMutual capacitance
Why: Mutual inductance between the windings induces the secondary voltage.
- G5C02Question 2
What is the output voltage if an input signal is applied to the secondary winding of a 4:1 voltage step-down transformer instead of the primary winding?
- AThe input voltage is multiplied by 4 Correct
- BThe input voltage is divided by 4
- CAdditional resistance must be added in series with the primary to prevent overload
- DAdditional resistance must be added in parallel with the secondary to prevent overload
Why: Driving the secondary of a 4:1 step-down transformer steps the voltage up by 4.
- G5C03Question 3
What is the total resistance of a 10-, a 20-, and a 50-ohm resistor connected in parallel?
- A5.9 ohms Correct
- B0.17 ohms
- C17 ohms
- D80 ohms
Why: 1 ÷ (1/10 + 1/20 + 1/50) = 1 ÷ 0.17 ≈ 5.9 Ω.
- G5C04Question 4
What is the approximate total resistance of a 100- and a 200-ohm resistor in parallel?
- A300 ohms
- B150 ohms
- C75 ohms
- D67 ohms Correct
Why: (100 × 200) ÷ (100 + 200) ≈ 67 Ω.
- G5C05Question 5
Why is the primary winding wire of a voltage step-up transformer usually a larger size than that of the secondary winding?
- ATo improve the coupling between the primary and secondary
- BTo accommodate the higher current of the primary Correct
- CTo prevent parasitic oscillations due to resistive losses in the primary
- DTo ensure that the volume of the primary winding is equal to the volume of the secondary winding
Why: In a step-up transformer the primary carries more current, so it needs heavier wire.
- G5C06Question 6
What is the voltage output of a transformer with a 500-turn primary and a 1500-turn secondary when 120 VAC is applied to the primary?
- A360 volts Correct
- B120 volts
- C40 volts
- D25.5 volts
Why: The turns ratio is 1:3, so 120 V × 3 = 360 V.
- G5C07Question 7
What transformer turns ratio matches an antenna’s 600-ohm feed point impedance to a 50-ohm coaxial cable?
- A3.5 to 1 Correct
- B12 to 1
- C24 to 1
- D144 to 1
Why: Turns ratio = √(600 ÷ 50) = √12 ≈ 3.5:1.
- G5C08Question 8
What is the equivalent capacitance of two 5.0-nanofarad capacitors and one 750-picofarad capacitor connected in parallel?
- A576.9 nanofarads
- B1,733 picofarads
- C3,583 picofarads
- D10.750 nanofarads Correct
Why: Parallel capacitors add: 5 + 5 + 0.75 = 10.75 nF.
- G5C09Question 9
What is the capacitance of three 100-microfarad capacitors connected in series?
- A0.33 microfarads
- B3.0 microfarads
- C33.3 microfarads Correct
- D300 microfarads
Why: Three equal capacitors in series: 100 ÷ 3 ≈ 33.3 µF.
- G5C10Question 10
What is the inductance of three 10-millihenry inductors connected in parallel?
- A0.30 henries
- B3.3 henries
- C3.3 millihenries Correct
- D30 millihenries
Why: Three equal inductors in parallel: 10 ÷ 3 ≈ 3.3 mH.
- G5C11Question 11
What is the inductance of a circuit with a 20-millihenry inductor connected in series with a 50-millihenry inductor?
- A7 millihenries
- B14.3 millihenries
- C70 millihenries Correct
- D1,000 millihenries
Why: Inductors in series add: 20 + 50 = 70 mH.
- G5C12Question 12
What is the capacitance of a 20-microfarad capacitor connected in series with a 50-microfarad capacitor?
- A0.07 microfarads
- B14.3 microfarads Correct
- C70 microfarads
- D1,000 microfarads
Why: (20 × 50) ÷ (20 + 50) ≈ 14.3 µF.
- G5C13Question 13
Which of the following components should be added to a capacitor to increase the capacitance?
- AAn inductor in series
- BAn inductor in parallel
- CA capacitor in parallel Correct
- DA capacitor in series
Why: Capacitors in parallel add, increasing capacitance.
- G5C14Question 14
Which of the following components should be added to an inductor to increase the inductance?
- AA capacitor in series
- BA capacitor in parallel
- CAn inductor in parallel
- DAn inductor in series Correct
Why: Inductors in series add, increasing inductance.