Question

What is the equivalent resistance of an ammeter that has a coil resistance of $1k\Omega$, and a shunt resistance of $1\Omega$?

• A. $1.01\Omega$
• B. $0.99\Omega$
• C. $1\Omega$
• D. $10\Omega$

Answer 1

The correct option is B $0.99\Omega$

The shunt resistor is connected in parallel to the ammeter coil.
Here, $R=1k\Omega =1000\Omega$
$R_s=1\Omega$
Before even starting the calculation, you should expect an answer which is less than $1\Omega$ , because in the parallel combination of resistors the net resistance comes out to be smaller than either of the resistors.
Now, $\frac{1}{R_{eq}}=\frac{1}{R}+\frac{1}{R_s}$
$R_{eq}=\frac{1000}{1001}=0.999\Omega$.