Question E6A10:
In Figure E6-1, which is the schematic symbol for an N-channel dual-gate MOSFET?  

Choices:  
A: 2  
B: 4  
C: 5  
D: 6    

Correct Answer is  B: 4  

Correct answer: 4

Why 4 is correct:
- Symbol 4 shows a MOSFET with two insulated gates (two separate gate electrodes drawn as parallel plates separated from the channel), which is the hallmark of a dual-gate MOSFET.
- It is N-channel: the substrate/body arrow is oriented for N-channel (rule of thumb below: for MOSFETs, the N-channel arrow points in).

Why the others are incorrect:
- Choice 2: This is a JFET (the gate connects directly to the channel junction rather than being insulated). It also has only one gate, not dual-gate.
- Choice 5: Dual-gate MOSFET but P-channel (arrow orientation is opposite; see arrow rule).
- Choice 6: A single-gate MOSFET (only one gate electrode shown), so not a dual-gate device.

Useful rules of thumb:
- MOSFET vs JFET symbol:
  - MOSFET gate is insulated: drawn as a gate electrode separated by a gap from the channel (capacitor-like).
  - JFET gate forms a junction: gate line touches the channel.
- Dual-gate MOSFET: two separate gate electrodes (G1 and G2) along the same channel.
- Arrow direction mnemonic for FETs: $ \text{Arrow points from P to N} $.
  - For MOSFETs: N-channel arrow points in; P-channel arrow points out.