Amateur Extra E5D: Parasitics, skin effect and reactive power
These are the 12 official questions in group E5D of the 2024–2028 Amateur Extra 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.
- E5D01Question 1
What is the result of conductor skin effect?
- AResistance increases as frequency increases because RF current flows closer to the surface Correct
- BResistance decreases as frequency increases because electron mobility increases
- CResistance increases as temperature increases because of the change in thermal coefficient
- DResistance decreases as temperature increases because of the change in thermal coefficient
Why: Skin effect pushes RF current to the surface, so resistance rises with frequency.
- E5D02Question 2
Why is it important to keep lead lengths short for components used in circuits for VHF and above?
- ATo increase the thermal time constant
- BTo minimize inductive reactance Correct
- CTo maintain component lifetime
- DAll these choices are correct
Why: Short leads minimize inductive reactance at VHF and above.
- E5D03Question 3
What is the phase relationship between current and voltage for reactive power?
- AThey are out of phase
- BThey are in phase
- CThey are 90 degrees out of phase Correct
- DThey are 45 degrees out of phase
Why: With reactive power, voltage and current are 90 degrees out of phase.
- E5D04Question 4
Why are short connections used at microwave frequencies?
- ATo increase neutralizing resistance
- BTo reduce phase shift along the connection Correct
- CTo increase compensating capacitance
- DTo reduce noise figure
Why: Short connections reduce phase shift at microwave frequencies.
- E5D05Question 5
What parasitic characteristic causes electrolytic capacitors to be unsuitable for use at RF?
- ASkin effect
- BShunt capacitance
- CInductance Correct
- DDielectric leakage
Why: Electrolytic capacitors have too much inductance for RF.
- E5D06Question 6
What parasitic characteristic creates an inductor’s self-resonance?
- ASkin effect
- BDielectric loss
- CCoupling
- DInter-turn capacitance Correct
Why: Inter-turn capacitance makes an inductor self-resonant.
- E5D07Question 7
What combines to create the self-resonance of a component?
- AThe component’s resistance and reactance
- BThe component’s nominal and parasitic reactance Correct
- CThe component’s inductance and capacitance
- DThe component’s electrical length and impedance
Why: A part's nominal and parasitic reactances combine to make it self-resonant.
- E5D08Question 8
What is the primary cause of loss in film capacitors at RF?
- AInductance
- BDielectric loss
- CSelf-discharge
- DSkin effect Correct
Why: Skin effect is the main loss in film capacitors at RF.
- E5D09Question 9
What happens to reactive power in ideal inductors and capacitors?
- AIt is dissipated as heat in the circuit
- BEnergy is stored in magnetic or electric fields, but power is not dissipated Correct
- CIt is canceled by Coulomb forces in the capacitor and inductor
- DIt is dissipated in the formation of inductive and capacitive fields
Why: Ideal L and C store energy in their fields and dissipate none.
- E5D10Question 10
As a conductor’s diameter increases, what is the effect on its electrical length?
- AThickness has no effect on electrical length
- BIt varies randomly
- CIt decreases
- DIt increases Correct
Why: A thicker conductor is electrically longer.
- E5D11Question 11
How much real power is consumed in a circuit consisting of a 100-ohm resistor in series with a 100-ohm inductive reactance drawing 1 ampere?
- A70.7 watts
- B100 watts Correct
- C141.4 watts
- D200 watts
Why: Only resistance uses real power: 1² × 100 = 100 W.
- E5D12Question 12
What is reactive power?
- APower consumed in circuit Q
- BPower consumed by an inductor’s wire resistance
- CThe power consumed in inductors and capacitors
- DWattless, nonproductive power Correct
Why: Reactive power is wattless, nonproductive power.