Question

An analog ammeter able to have a 0.5 A maximum reading is to be built using a small coil of resistance R = 20 Ω, and full scale deflection at 1 mA. What resistance should be added to this coil and how should it be connected to the coil?

Answer 1

Answer:

The resistance added to this coil is 0.04 ohm in parallel.

Explanation:

Given that,

Current I'= 0.5 A

Resistance R= 20 ohm

Deflection I= 1 mA

We need to calculate the resistance

Using ohm's law

$V = I R$

Where,

V = voltage

I =current

R = resistance

V is constant so ,

Therefore,

I R=I'R'

$R'=\dfrac{I}{I'}\times R$

$R'=\dfrac{0.001}{0.5}\times20$

$R'=0.04\ \Omega$

Hence, The resistance added to this coil is 0.04 ohm in parallel.