Question

the ratio of equivalent resistance across A and B when switch is open to that when switch is closed is

Answer 1

when switch is open then
Req=18 parallel 18 
       =18*18/(18+18)
       =9 ohms
when switch is closed
Req=6+6=12 ohms    (because current will chose path with least resistance)
so the ratio will be-
=9/12
=3/4 answer

Answer 2

Here your answer goes

Case :- I

If Circuit is open then

12 + 6 = 18

Parallel Combination

⇒  $\frac{18*18}{(18+18)}$

⇒ $\frac{324}{36}$

⇒ 9 Ohm

Case :- 2

If Circuit is Closed then

Series Combination

⇒ 6+6

⇒ 12 ohm

Therefore , the ratio will be

⇒  $\frac{9}{12}$

⇒ $\frac{3}{4}$

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