GATE | Gate IT 2005 | Question 10

A two-way switch has three terminals a, b and c. In ON position (logic value 1), a is connected to b, and in OFF position, a is connected to c. Two of these two-way switches S1 and S2 are connected to a bulb as shown below.p1

Which of the following expressions, if true, will always result in the lighting of the bulb ?
(A) S1.S2′
(B) S1+S2
(C) (S1⊕S2)’
(D) S1⊕S2

Answer: (C)

Explanation: If we draw truth table of the above circuit,it’ll be

S1     S2    Bulb
0         0       On
0         1        Off
1         0        Off
1          1         On
= (S1⊕ S2)’


Therefore answer is C

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