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The effect of closing the key K in the circuit shown abov...

The effect of closing the key K in the circuit shown above would be to

The effect of closing the key K in the circuit shown above would be to

A.

increase the current by 0.6A

B.

reduce the current by 0.6A

C.

increase the current by 0.4A

D.

keep the current unchanged

View answer & explanation

Correct answer is C

When K is open, the total resistance

R = 8 $\Omega$ + 2 $\Omega$ = 10 $\Omega$

I = $\frac{V}{R}$ = $\frac{6}{10}$

= 0.6A

When K is closed, we have

$\frac{1}{R}$ = $\frac{1}{8}$ + $\frac{1}{8}$

⇒ $\frac{1}{R}$ = $\frac{1}{4}$

⇒ R = 4 $\Omega$

The total resistance R = 4 $\Omega$ + 2 $\Omega$

= 6 $\Omega$

I = $\frac{6}{6}$

= 1A

Hence, I = 1A - 0.6A = 0.4A increase

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