Question 14 Marks
Simplify the following so that the new circuit has minimum number of switches. Also, draw the simplified circuit.


Answer
View full question & answer→(ii) Let $p :$ the switch $S_1$ is closed
$q :$ the switch $S_2$ is closed
$r :$ the switch $S_3$ is closed
$s :$ the switch $S_4$ is closed
$t :$ the switch $S_5$ is closed
$\sim p :$ the switch $S_1‘$ is closed or the switch $S_1$ is open
$\sim q :$ the switch $S_2‘$ is closed or the switch $S_2$ is open
$\sim r :$ the switch $S_3‘$ is closed or the switch $S_3$ is open
$\sim s :$ the switch $S_4‘$ is closed or the switch $S_4$ is open
$\sim t :$ the switch $S_5‘$ is closed or the switch $S_5$ is open.
Then the given circuit in symbolic form is
$[(p ∧ q) ∨ \sim r ∨ \sim s ∨ \sim t] ∧ [(p ∧ q) ∨ (r ∧ s ∧ t)]$
Using the laws of logic, we have,
$[(p ∧ q) ∨ \sim r ∨ \sim s ∨ \sim t] ∧ [(p A q) ∨ (r ∧ s ∧ t)]$
$= [(p∧ q) ∨ \sim (r ∧ s ∧ t)] ∧ [(p ∧ q) ∨ (r ∧ s ∧ t)] … ($By De Morgan’s Law$)$
$= (p ∧ q) ∨ [ \sim (r ∧ s ∧ t) ∧ (r ∧ s ∧ t)] … ($By Distributive Law$)$
$= (p ∧ q) ∨ F … ($By Complement Law$)$
$= p ∧ q … ($By Identity Law$)$
Hence, the alternative simplified circuit is :

$q :$ the switch $S_2$ is closed
$r :$ the switch $S_3$ is closed
$s :$ the switch $S_4$ is closed
$t :$ the switch $S_5$ is closed
$\sim p :$ the switch $S_1‘$ is closed or the switch $S_1$ is open
$\sim q :$ the switch $S_2‘$ is closed or the switch $S_2$ is open
$\sim r :$ the switch $S_3‘$ is closed or the switch $S_3$ is open
$\sim s :$ the switch $S_4‘$ is closed or the switch $S_4$ is open
$\sim t :$ the switch $S_5‘$ is closed or the switch $S_5$ is open.
Then the given circuit in symbolic form is
$[(p ∧ q) ∨ \sim r ∨ \sim s ∨ \sim t] ∧ [(p ∧ q) ∨ (r ∧ s ∧ t)]$
Using the laws of logic, we have,
$[(p ∧ q) ∨ \sim r ∨ \sim s ∨ \sim t] ∧ [(p A q) ∨ (r ∧ s ∧ t)]$
$= [(p∧ q) ∨ \sim (r ∧ s ∧ t)] ∧ [(p ∧ q) ∨ (r ∧ s ∧ t)] … ($By De Morgan’s Law$)$
$= (p ∧ q) ∨ [ \sim (r ∧ s ∧ t) ∧ (r ∧ s ∧ t)] … ($By Distributive Law$)$
$= (p ∧ q) ∨ F … ($By Complement Law$)$
$= p ∧ q … ($By Identity Law$)$
Hence, the alternative simplified circuit is :








