Question

An ammeter has a coil of resistance 5 d fitted with a shunt of resistance 1ohm. It is connected in a circuit in which the
current is 0.9 A. The current through the coil will be
a) 0.15 A
b) 0.75 A
c) 0.18 A
d) 0.72A​

Answer 1

Answer:

0.15 A.

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Answer 2

Answer:

The current through the coil will be 0.15A i.e.option(a).

Explanation:

The current through the coil will be calculated as,

$I=\frac{V}{R}$           (1)

Where,

I=current through the coil

V=potential difference across the coil

R=the resistance of the coil

From the question we have,

The resistance of the coil(R₁)=5Ω

The resistance of the shunt(R₂)=1Ω

The total current flowing through the circuit(I')=0.9A

We know that for a coil to be converted into an ammeter a shunt is connected in parallel with the coil. So, the equivalent resistance will be calculated as,

$R=\frac{R_1R_2}{R_1+R_2}$   (2)

By inserting the variables in equation (2) we get;

$R=\frac{5\times 1}{5+1}$

$R=\frac{5}{6}$      (3)

The potential across the whole circuit is calculated as,

$V=I'R$     (4)

By inserting the variables in equation (4) we get;

$V=0.9\times \frac{5}{6}$

$V=0.75\ volt$    (6)

Now the current through the coil will be,

$I=\frac{0.75}{5}$

$I=0.15A$

Hence, the correct answer is 0.15A i.e.option(a).

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