An ammeter of internal resistance is used to measure the current drawn from an ideal…

PHYSICS · Subjective · CBSE · Physics · Current Electricity · Current Electricity

Problem

An ammeter of internal resistance

R_{\mathrm A}

is used to measure the current drawn from an ideal cell through a load resistor

R_{\mathrm L}

. (i) Derive an expression for the percentage error in the current reading produced by the finite internal resistance of the ammeter. Express your result in terms of

R_{\mathrm A}

and

R_{\mathrm L}

. (ii) For

R_{\mathrm L}=8\,\Omega

and

R_{\mathrm A}=0.40\,\Omega

, calculate the true current and the current indicated by the ammeter when the cell emf is 6\,V. Hence find the percentage error. (iii) What maximum value of

R_{\mathrm A}

would keep the percentage error in the current measurement below 2\% for the same load resistor and cell emf?

Related theory

Cells & EMF
Compound Circuits
EMF, internal resistance and terminal voltage
Electricity
EMF and internal resistance
Current Electricity
Cells emf and internal resistance

Browse the problem library