Question

Consider the given circuit diagram of switching of light from two different switches.
The input condition needed to turn on LED is

• A. A = B = 1
• B. A = B = 0
• C. A = 1 ; B = 0
• D. Both (a) and (b)

Answer 1

The correct option is D Both (a) and (b)

From the circuit diagram, we deduce that LED will glow when Z = low (0) and Z will be low only when X or Y or both will be high. Now, we consider the different input conditions as
1. For A = B = 1 ;
X = 1 and Y = 0
$\Rightarrow$ Z = 0 ; LED glows

2. For A = B = 0 ;
X = 0 and Y =1
$\Rightarrow$ Z = 0 ; LED glows

3. For A = 0, B = 1 ;
X = 0 and Y = 0
$\Rightarrow$ Z = 1 ; LED does not glows

4. For A =1, B = 0 ;
X = 0 and Y =0
$\Rightarrow$ Z = 1 ; LED does not glows