Two identical moving coil galvanometers have $$10$$Ω resistance and full scale deflection at $$2$$μA current. One of them is converted into a voltmeter of $$100mV$$ full scale reading and the order into an Ammeter of $$1mA$$ full scale current using appropriate resistors. These are then used to measure the voltage and current in the Ohm’s law experiment with $$R=1000$$Ω resistor by using an ideal cell. Which of the following $$statement(s)$$ $$is/are$$ correct?

Question

Two identical moving coil galvanometers have $$10$$Ω resistance and full scale deflection at $$2$$μA current. One of them is converted into a voltmeter of $$100mV$$ full scale reading and the order into an Ammeter of $$1mA$$ full scale current using appropriate resistors. These are then used to measure the voltage and current in the Ohm’s law experiment with $$R=1000$$Ω  resistor by using an ideal cell. Which of the following $$statement(s)$$ $$is/are$$ correct?

Infinity Learn · Accepted Answer

Option $$4$$:    $$IgG=IRA$$    ⇒$$2$$×$$10$$−$$610=1$$×$$10$$−$$3RA$$ ∴ Resistance of ammeter $$RA=0.02$$Ω  (4)  is correctOption $$3$$: $$V=IgRV$$  ∴$$RV=VIg=10$$−$$12$$×$$10$$−$$6=5$$×$$104$$Ω   $$=50k$$Ω ∴(3) is wrongOption $$2$$: $$R1=R$$.$$RVR+RV$$,$$R2=RA$$  Reading of ammeter $$=$$ IReading of voltmeter V $$=$$ IRMeasured value of resistance is $$Rm=VI=R1$$ $$=R$$.$$RVR+RV=103$$×$$5$$×$$104103+5$$×$$104=5$$×$$10451=980.4$$Ω  ∴$$2$$ is correctOption $$1$$: measured value of R depends on R and RV only, but independent of RA and r values.  Measured value of resistance will again be $$980.4$$Ω only

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