Amateur Extra E6A: Semiconductors and transistors
These are the 12 official questions in group E6A 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.
- E6A01Question 1
In what application is gallium arsenide used as a semiconductor material?
- AIn high-current rectifier circuits
- BIn high-power audio circuits
- CIn microwave circuits Correct
- DIn very low-frequency RF circuits
Why: Gallium arsenide is used in microwave circuits.
- E6A02Question 2
Which of the following semiconductor materials contains excess free electrons?
- AN-type Correct
- BP-type
- CBipolar
- DInsulated gate
Why: N-type material has extra free electrons.
- E6A03Question 3
Why does a PN-junction diode not conduct current when reverse biased?
- AOnly P-type semiconductor material can conduct current
- BOnly N-type semiconductor material can conduct current
- CHoles in P-type material and electrons in the N-type material are separated by the applied voltage, widening the depletion region Correct
- DExcess holes in P-type material combine with the electrons in N-type material, converting the entire diode into an insulator
Why: Reverse bias separates holes and electrons and widens the depletion region, so no current flows.
- E6A04Question 4
What is the name given to an impurity atom that adds holes to a semiconductor crystal structure?
- AInsulator impurity
- BN-type impurity
- CAcceptor impurity Correct
- DDonor impurity
Why: An impurity that adds holes is called an acceptor.
- E6A05Question 5
How does DC input impedance at the gate of a field-effect transistor (FET) compare with that of a bipolar transistor?
- AThey are both low impedance
- BAn FET has lower input impedance
- CAn FET has higher input impedance Correct
- DThey are both high impedance
Why: A FET has much higher gate input impedance than a bipolar transistor.
- E6A06Question 6
What is the beta of a bipolar junction transistor?
- AThe frequency at which the current gain is reduced to 0.707
- BThe change in collector current with respect to the change in base current Correct
- CThe breakdown voltage of the base-to-collector junction
- DThe switching speed
Why: Beta is the change in collector current divided by the change in base current.
- E6A07Question 7
Which of the following indicates that a silicon NPN junction transistor is biased on?
- ABase-to-emitter resistance of approximately 6 ohms to 7 ohms
- BBase-to-emitter resistance of approximately 0.6 ohms to 0.7 ohms
- CBase-to-emitter voltage of approximately 6 volts to 7 volts
- DBase-to-emitter voltage of approximately 0.6 volts to 0.7 volts Correct
Why: A silicon NPN transistor is on at about 0.6–0.7 V base-emitter.
- E6A08Question 8
What is the term for the frequency at which the grounded-base current gain of a bipolar junction transistor has decreased to 0.7 of the gain obtainable at 1 kHz?
- ACorner frequency
- BAlpha rejection frequency
- CBeta cutoff frequency
- DAlpha cutoff frequency Correct
Why: The alpha cutoff frequency is where grounded-base gain falls to 0.7 of its 1 kHz value.
- E6A09Question 9
What is a depletion-mode field-effect transistor (FET)?
- AAn FET that exhibits a current flow between source and drain when no gate voltage is applied Correct
- BAn FET that has no current flow between source and drain when no gate voltage is applied
- CAn FET that exhibits very high electron mobility due to a lack of holes in the N-type material
- DAn FET for which holes are the majority carriers
Why: A depletion-mode FET conducts with no gate voltage applied.
- E6A10Question 10
In Figure E6-1, which is the schematic symbol for an N-channel dual-gate MOSFET?
- A2
- B4 Correct
- C5
- D6
Why: Symbol 4 in E6-1 is an N-channel dual-gate MOSFET.
- E6A11Question 11
In Figure E6-1, which is the schematic symbol for a P-channel junction FET?
- A1 Correct
- B2
- C3
- D6
Why: Symbol 1 in E6-1 is a P-channel junction FET.
- E6A12Question 12
What is the purpose of connecting Zener diodes between a MOSFET gate and its source or drain?
- ATo provide a voltage reference for the correct amount of reverse-bias gate voltage
- BTo protect the substrate from excessive voltages
- CTo keep the gate voltage within specifications and prevent the device from overheating
- DTo protect the gate from static damage Correct
Why: Zener diodes protect a MOSFET gate from static damage.