A bulb in a stair case has two switches, one switch being at ground floor and other one at first floor. The bulb can be turned on and also can be turned off by any one of the switches irrespective of the state of other switch.The logic of switching of bulb resembles

A bulb in a stair case has two switches, one switch being at ground floor and other one at first floor. The bulb can be turned on and also can be turned off by any one of the switches irrespective of the state of other switch.The logic of switching of bulb resembles

(GATE-EC-2013)

(a) an AND gate
(b) an OR gate
(c) an XOR gate
(d) an NAND gate



ANS: C


EXPLANATORY ANSWER:

The purpose of staircase wiring is, one should be able to switch on and switch off lights from more than one point and these can be achieved by 2-way switches.The position of switches A, B and the condition of the lamp can be tabulated as below.

(i.e)  lamp glows when  switch A & B positions are different.

This truth table simply resembles the logic of a XOR gate as shown below

From the truth table it can be verified that XOR logic is implemented.