An ammeter

Question

An ammeter

Examoogle · Accepted Answer

Is inserted in series in a circuit and current to be measured flows through it

Explanation: An ammeter is a measuring instrument used to determine the electric current in a circuit. To ensure all the current to be measured passes through the meter, it is connected in series with the load.

Working Principle: The ammeter works on the principle of electromagnetic deflection, thermal effect, or digital integration. Since it must measure the current flow, it is inserted directly into the conductive path. An ideal ammeter has zero internal resistance to prevent voltage drop and ensure minimal circuit disturbance.

Key Formulas: $R_{sh} = \frac{I_m R_m}{I - I_m}$ — Shunt resistance required to extend the range of an ammeter; $I_{total} = I_{meter}$ — Current condition in a series circuit

Key Points: Ammeters are placed in series to ensure the total branch current flows through the moving coil.; An ideal ammeter has an internal resistance of $0\ \Omega$.; Connecting an ammeter in parallel would act as a short circuit, potentially damaging the device due to excessive current.; The shunt resistor ($R_{sh}$) is used in parallel with the galvanometer to allow only a fraction of current to pass through the meter movement.

Advantages: Direct measurement of current flow.; Simple integration into existing series circuits.

Disadvantages: Introduction of small measurement error due to internal resistance.; Risk of damage if connected in parallel across a voltage source.

Applications: Laboratory current measurement.; Industrial power monitoring.; Automotive electrical diagnostics.

Additional Info: If an ammeter is connected in parallel, it acts as a short circuit because its resistance is very low, which could blow the fuse or damage the instrument.. Option B is incorrect because if only part of the current flowed through the meter, it would not represent the total current of the series branch.

Answer: A is correct — An ammeter must be connected in series so that the entirety of the current in the branch passes through the measuring element.

Exam Tip: Always remember: Voltmeters go in parallel (high resistance) and Ammeters go in series (low resistance).

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