# NCERT Physics Class 12 Exemplar Ch 14 Semiconductor Electronics Materials Devices and Simple Circuits Part 3

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26 Two car garages have a common gate which needs to open automatically when a car enters either of the garages or cars enter both. Devise a circuit that resembles this situation using diodes for this situation.

Ans:

OR gate gives output according to the truth table.

 A B C 0 0 0 0 1 1 1 0 1 1 1 1

Q 27 How would you set up a circuit to obtain NOT gate using a transistor?

 Input Output A A 0 1 1 0

Q 28 Explain why elemental semiconductor cannot be used to make visible LEDs.

Elemental semiconductor’s band-gap is such that emissions are in IR region.

Q 29 Write the truth table for the circuit shown in Fig.

Name the gate that the circuit resembles.

Ans:

Truth table

 A B Y 0 0 0 0 1 0 1 0 0 1 1 1

AND Gate

Q 30 A Zener of power rating 1 W is to be used as a voltage regulator. If Zener has a breakdown of and it has to regulate voltage which fluctuated between and, what should be the value of Rs for safe operation (Fig.)?

And:

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