The electronic circuit shown in the figure represents a
When A is connected to ground, base emitter junction is not forward based so the transistor will not conduct and current through is zero. Hence is when A = 0, Y = 1.
Again when A is connected to P, base-emitter junction is forward biased and collector-emitter junction is reverse biased. So the transistor conducts and current through is equal to . In this case . So when . Hence the circuit represents a NOT gate