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

Explanation

The NOT gate is a device which has only one input and one output i.e., `bar(A) = Y` means Y equal NOT A.
This gate cannot be realised by using diodes. However it can be realised by making use of a transistor. This can be seen in the figure given below.

Here, the base B of the transistor is connected to the input A through a resistance `R_(b)` and the emitter E is earthed. The collected to 5 V battery. The output Y is the voltage at C w.r.t. earth.
The resistor `R_(b) " and " R_(c)` are so chosen that if emitter-base junction is unbiased, the transistor is in cut off mode and it emitter-base junction is forward biased by `5V`, the transistor is in saturation state.