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Conversion of Galvanometer to Ammeter problem

Diagram of D'Arsonval/Weston type galvanometer.
Diagram of D'Arsonval/Weston type galvanometer. (Photo credit: Wikipedia)

A galvanometer can be converted to ammeter by connecting a low resistance, called shunt in parallel with it. If a galvanometer of resistance 45 Ω is shunted by a resistance of 5 Ω what fraction of main current passes through the  Galvanometer? What is the current which flows through the shunt?

 

Wire Gauge and Resistance problem

I am using 18 gauge nicrome wire having ohm of 17.3 , 220 volt. I want to use 10 gauge wire how to decide the length?

Padmanava asked

Answer:

18 gauge corresponds to a diameter of 1.22 mm

Therefore radius r1= 1.22/2=0.61 mm=0.00061m

10 gauge means diameter is 3.25 mm

Radius r2 = 3.25/2=1.625mm=0.001625m

Sine the resistance needs to be the same, we can use the formula


Which gives

As resistivity is same.

Substitute the values and you will get the answer.

Is ohm’s law universally applicable?

Amritha asked:

“Is ohm’s law universally applicable?”

Answer:

The Ohm’s law states that “The current through a conductor is directly proportional to the potential difference applied across its ends provided the physical conditions such as temperature remains the same

From the statement it is implied that it is not a universal law, and is applicable to conductors. It is not valid for semiconductors and electronic devices.

The substances which obey Ohm’s law are said to be ohmic and those which do not obey Ohm’s law are “Non Ohmic

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