Following gates section is connected in a complete suitable circuit. [figure] For which of the following combination, bulb will glow (ON) :
- A = 1, B = 1, C = 1, D = 0
- A = 1, B = 0, C = 0, D = 0
- A = 0, B = 0, C = 0, D = 1
- A = 0, B = 1, C = 1, D = 1
Answer
(2) A = 1, B = 0, C = 0, D = 0
Solution
Bulb glows only when its two ends are at different levels (one 1, the other 0).
Upper end of bulb: Y1 = A + BC = A BC
Lower end of bulb: Y2 = D
(A): Y1 = 1, Y2 = 1 ⇒ (A) is OFF
(B): Y1 = 0, Y2 = 1 ⇒ (B) is ON
(C): Y1 = 0, Y2 = 0 ⇒ (C) is OFF
(D): Y1 = 0, Y2 = 0 ⇒ (D) is OFF
Answer: (2)