Electronic Devices and Circuits Multiple Choice Questions on “The Junction Field-Effect Transistor – 1”.
1. FET is a voltage controlled device.
A. True
B. False
Answer: A
Clarification: Field Effect Transistors are voltage controlled devices, by applying some voltage between the gate and source, the drain current can be controlleC. In order to control the operation of FET the gate to drain voltage is varied to operate the FET in different regions of operation.
2. Which of the following statement is true about FET?
A. It has high output impedance
B. It has high input impedance
C. It has low input impedance
D. It does not offer any resistance
Answer: B
Clarification: Because of the Sio2 insulator, doped between drain and source at the top, the resistance offered by this is very high. The insulator will stop the flow of electron from one part to another which acts as an open circuit.
3. Comparing the size of BJT and FET, choose the correct statement?
A. BJT is larger than the FET
B. BJT is smaller than the FET
C. Both are of same size
D. Depends on application
Answer: A
Clarification: BJT usually are built with a thickness of up to 1cm whereas the FET uses a fabrication technique which makes its size in mm.
4. What is the main advantage of FET which makes it more useful in industrial applications?
A. Voltage controlled operation
B. Less cost
C. Small size
D. Semiconductor device
Answer: C
Clarification: Because of its small size, the IC chips can be made even smaller which reduces the wear and tear. The process technology used with process technology constant a which is the ratio of Width and Length, the FET is made more advantageous.
5. For a FET when will maximum current flows?
A. Vgs = 0V
B. Vgs = 0v and Vds >= |Vp|
C. VDS >= |Vp|
D. Vp = 0
Answer: B
Clarification: For a FET the current reaches maximum that is IDSS occurs when Vgs = 0V and VDS >= |Vp|
6. What is the value of current when the gate to source voltage is less than the pinch off voltage?
A. 1A
B. 5A
C. 100A
D. 0
Answer: D
Clarification: When the gate to source voltage is less than pinch off, both of the junctions will be reverse biased and hence no current flows.
7. The Shockley equation is __________________
A. ID = (1 – Vgs/Vp)2
B. ID = IDSS (1 – Vgs/Vp)2
C. ID = IDSS (1 – Vgs/Vp)1
D. ID = IDSS (1 + Vgs/Vp)2
Answer: B
Clarification: By using the diode equation Shockley derived the equation between the drain current and voltage Vgs.
8. What is the value of drain current when Vgs=pinch off voltage?
A. 0A
B. 1A
C. 2A
D. Cannot be determined
Answer: A
Clarification: ID = IDSS (1-Vgs/Vp)2
If Vgs = Vp,then
ID = IDSS (1-1)=0.
9. To use FET as a voltage controlled resistor, in which region it should operate?
A. Ohmic region
B. cut off
C. Saturation
D. cut off and saturation