A MOSFET differs from the JFET because 1. of the characteristics 2. the MOSFET has two gates 3. the JFET has p-n junctions 4. of the physical reduced size
1 & 3
Statement 3 names the fundamental structural difference and statement 1 names its visible consequence — so the answer is 1 & 3, option 2.
Statement 3 — the physics. A JFET's gate is a reverse-biased p-n junction, and its depletion region squeezes the channel. A MOSFET's gate is a metal or polysilicon plate separated from the channel by an insulating oxide; there is no junction anywhere near it. That one difference produces every other:
| JFET | MOSFET | |
|---|---|---|
| Gate | p-n junction | Insulated by SiO2 |
| Gate current | Small leakage, nA | Essentially zero, pA |
| Input impedance | ~109 Ω | ~1014 Ω |
| Gate polarity | Reverse bias only | Either polarity |
| Modes | Depletion only | Depletion and enhancement |
Statement 1 — the characteristics. This follows directly. Because the JFET's gate junction must stay reverse biased, forward bias would make it conduct, so the gate can only ever reduce the channel: the JFET is a depletion-mode device with the channel present at \(V_{GS}=0\). The MOSFET's oxide permits gate voltage of either sign, so an enhancement device is possible, one with no channel at all until the gate creates an inversion layer:
\(I_{D}=K\left(V_{GS}-V_{T}\right)^{2}\qquad\text{for}\ V_{GS}\gt V_{T}\)
Its transfer curve sits entirely in the positive \(V_{GS}\) region, while the JFET's lies entirely in the negative — visibly different characteristics.
Why statement 2 is false. A MOSFET has one gate. Dual-gate MOSFETs exist and are used as mixers and AGC amplifiers, but they are a special type, not what distinguishes MOSFETs from JFETs. The four-terminal MOSFET's extra terminal is the substrate or body, not a second gate.
Why statement 4 is false as a distinguishing reason. MOSFETs are indeed the smaller devices — which is why integrated circuits are built from them and not from JFETs — but small size is a consequence of the fabrication process, not the reason the two device types differ in operation. The question asks what makes a MOSFET a different device.
Hence, statements 1 and 3 are correct.
Similar Questions
Match the following :
List - I List - II (figure in the original question) (a) n-channel Enhancement (Normally off) (i) 
(b) p-channel Depletion MOSFET (Normally on) (ii) 
(c) n-channel FET (iii) 
(d) p-channel Enhancement MOSFET (iv) 
Codes :
Important Questions from Types of FET
Match the following :
List - I List - II (figure in the original question) (a) n-channel Enhancement (Normally off) (i) (b) p-channel Depletion MOSFET (Normally on) (ii) (c) n-channel FET (iii) (d) p-channel Enhancement MOSFET (iv) Codes :
The pull up to pull down ratio for an n mos inverter driven by another n mos inverter can be evaluated from:
(A) Vi nv = V t − \(\rm\frac{V_{t d}}{\sqrt{Zpu/Zpd}}\)
(B) V inv = \(\rm\frac{−V_{t d}}{\sqrt{Zpu/Zpd}}\)
(C) \(\rm\frac{W_{pd}}{L_{pd}}\) (V inv − V t) 2= \(\rm\frac{W_{p u}}{L_{p u}}\) (−V td )2
(D) \(\rm\frac{W_{p d}}{L_{p d}}\) (V inv − V t ) = \(\rm\frac{W_{p u}}{L_{pu}}\) (−V td )2
Choose the correct answer from the options given below:
Match List I with List II:
List I List II (A) JFET (I) Two dimensional electron gas (B) MOSFET (II) Negative resistance device (C) Tunnel diode (III) Enhancement mode (D) HEMT (IV) Voltage controlled resistor Choose the correct answer from the options given below:
Which of the following is NOT a minority carrier semiconductor device ?
The metal gate that is insulated from the channel is also referred to as:
