Question

A) How do I measure resistance with an ammeter? B) How do I measure resistance with a voltmeter? (For both, Off Limits: you can’t use an ohmmeter) Can anybody explain with drawing schematics.

gauge resistivitiy only ampermeter and only voltmeter.Can I solve the problem just using Ohm's law

Answer 1

Suppose,you have an unknown resistor of resistance `R` attached in a circuit with a `V` volt of battery,and an ammeter.

So,if you record ammemter reading as `I A`,using Ohm's law,you get, `R=V/I`

Now,suppose in a circuit you had two unknown resistance of `R` and `R'`,with a voltmeter attached in parallel to `R`.The circuit was connected to a battery of `V` volt.

So,if the voltmeter reads `v` Volt,then we can say potential drop across the resistor is `v`,and potential drop across `R'` is `V-v`

So,we can write, `V=v+(V-v)`

or, `V=v+IR'` (let,current flowing through the circuit is `I`)

so, `I=(V-v)/(R')`

Again, `I=v/R`

so, `(V-v)/(R') =v/R`

or, `R=((V-v)/v)R'`

So,if you know the value of `R'` at least you can calculate `R`