QJEEM21Ph1708: JEE Main 2021 Physics - Class 12 JEEM21Ph1708 Solution: If V A and V B are the input voltages (either 5V or 0V) and V 0 …

V_A = 5V $\Rightarrow$ A = 1

V_A = 0V $\Rightarrow$ A = 0

V_B = 5V $\Rightarrow$ B = 1

V_B = 0V $\Rightarrow$ B = 0

If A = B = 0, there is no potential anywhere here V₀ = 0

If A = 1, B = 0, Diode D₁ is forward biased, here V₀ = 5V

If A = 0, B = 1, Diode D₂ is forward biased hence V₀ = 5V

If A = 1, B = 1, Both diodes are forward biased hence V₀ = 5V

Truth table for I^st

$\therefore$ Given circuit is OR gate

For II^nd circuit

V_B = 5V, A = 1

V_B = 0V, A = 0

When A = 0, E - B junction is unbiased there is no current through it

$\therefore$ V₀ = 1

When A = 1, E-B junction is forward biased

V₀ = 0

$\therefore$ Hence this circuit is NOT gate