250+ TOP MCQs on The Pinch off Voltage Vp and Answers

Electronic Devices and Circuits Multiple Choice Questions on “The Pinch off Voltage Vp”.

1. What is pinch off voltage?
A. The minimum voltage required to turn on the FET
B. The maximum voltage a FET can withstand
C. Current amplification factor/voltage gain
D. The value of voltage at which the current gets pinched to zero
Answer: D
Clarification: Once the voltage difference between the gate and source goes near to the pinch off voltage, the channel will get pinched off resulting in off state of the FET, which makes no conventional current flow.

2. A p-channel Ge JFET has max-half channel width 5µm and channel conductivity of 2/Ωcm, if E_r = 2000cm²/VseC. What is the value of pinch off voltage?
A. 8.21V
B. 82.1V
C. 88.21V
D. 5.2V
Answer: C
Clarification: Vp=qN_A a²/2E
= (5×10^-4) (5×10^-4)×2/(2×16×8.854×2000×10^-14)
= 88.21V.

3. What will happen if gate voltage applied is positive to pinch off voltage?
A. Device burns
B. More current flows
C. Nothing happens
D. Current remains the same
Answer: A
Clarification: When the voltage applied across the gate terminal becomes more positive, all of the current will start flowing from drain to gate terminal. This results in breaking of insulator layer, resulting in device destruction.

4. How does a FET behave when the v-I characteristics are to the left of pinch off for an n channel FET?
A. Voltage controlled resistor
B. Amplifier
C. Switch
D. Diode
Answer: A
Clarification: When the voltage V_gs is less than pinch off voltage, there will be no current flow, resulting in Ohmic region, on controlling the V_gs and V_Ds values, the FET acts as Voltage controlled resistor.

5. What is the relation between the drain current and source current once the voltage crosses pinch off?
A. I_D = I_S
B. I_D = I_S + 1.5
C. I_D = 1/I_S
D. I_S – 2I_D = 0
Answer: A
Clarification: For a FET, once the voltage exceeds the pinch off voltage, the electrons will start flowing from source to drain or vice versa, since no current flows through the gate terminal, the current transfer takes place only between the drain and source. Hence I_D = I_S.

6. If a FET has a pinch off voltage =-1V and I_D=1mA, If V_gs=0V, What is the value of I_DSS?
A. 1A
B. 1mA
C. 0A
D. 100mA
Answer: B
Clarification: I_D=I_DSS (1-V_gs/V_p)²
V_gs=0V => : I_D=I_DSS=1mA.

7. For what value of V_gs, the drain current will be 1/4th of its maximum current?
A. 0
B. 1
C. V_p
D. V_p/2
Answer: D
Clarification: I_D=I_DSS (1-V_gs/V_p)²
When I_D=I_DSS/4 => (1-V_gs/V_p)² = 1/4
=>(1-V_gs/V_p)²=1/2
=>V_gs=V_p/2.

8. For a n-channel FET, what is the condition of V_gs for which the current becomes zero?
A. 0
B. 100V
C. V_p
D. Infinite
Answer: C
Clarification: I_D=I_DSS (1-V_gs/V_p)²
When ID=0, (1-V_gs/V_p)²=0
1=V_gs/V_p => V_gs=V_p.

9. For a FET having I_DSS=2mA V_gs=2V and V_p=-1V, What is the value of source current?
A. 9mA
B. 18mA
C. 3mA
D. 1mA
Answer: B
Clarification: I_D=I_DSS (1-V_gs/V_p)²
I_D=I_S=2×(1+2)(1+2)=3²×2=18mA
I_S=18mA.

10. Find the current through gate if the FET was given with gate to source voltage =10V and drain to source voltage =20V, the pinch off voltage was -2V and I_D=2mA.
A. 10mA
B. 20mA
C. 0mA
D. 2mA