Question

While studying the dependence of potential difference on current, what if the ammeter reading goes beyond the full scale? What remedy will you apply?

Answer 1

First of all you have to find out that how much current can be there in the circuit and select ammeter accordingly.

Ammeter with full deflection for a long time may lead to the burning and permanent damage to the ammeter coil and the shunt.

If there's no high current ammeter in the lab, then you can take the following steps:

We're going to convert an ammeter of 5A to an ammeter of 20A.

Let an ammeter with a range of 0 to 5A, and has a shunt of resistance 0.5Ω.

You need to measure a current of 7A in the circuit.

Then by formula,

$s = \frac{i(a)}{i - i(a)} \times r$

Where,

S = New shunt resistance

I(a) = Initial ammeter current

I = New ammeter current

r = Initial ammeter resistance

Putting values,

S = (5×0.5) ÷ (20-5)

S = 2.5/15

S = 0.1667Ω

This is the resistance which you'll connect in parallel with the ammeter to make it of the range of 20A...