Question

LED (light emitting diode) and logic gates circuit is given in figure. For what combination of \(A,B,C\) will both LEDs glow? 

• A. \(101\)
• B. \(100\)
• C. \(010\)
• D. \(001\)

Answer 1

The Correct Option is A

Concept: An LED glows when the output of the connected logic gate is \(1\). Step 1: First gate Inputs \(A\) and \(B\) go to an OR gate. \[ Y_1 = A + B \] LED\(_1\) glows when \[ A+B = 1 \] Step 2: Second gate Output of OR gate and input \(C\) pass through AND gates. \[ Y_2 = (A+B)\cdot C \] LED\(_2\) glows when \[ (A+B)=1 \quad \text{and} \quad C=1 \] Step 3: Find combination Take \[ A=1,\quad B=0 \] \[ A+B=1 \] For LED\(_2\): \[ C=1 \] Thus \[ (A,B,C) = (1,0,1) \] \[ \boxed{101} \]