Two identical moving coil galvanometer have resistance and full scale deflection at current.One of them is converted int…
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Two identical moving coil galvanometer have resistance and full scale deflection at current.One of them is converted into a voltmeter of full scale reading and the other into an Ammeter of full scale current using appropriate resistors. These are then used to measure the voltage and current in the Ohms law experiment with resistor by using an ideal cell. Which of the following statement(s) is/are correct ? [JEE Advanced 2019]
✓ Correct answer: a) The measured value of will be .
ExplanationWe have two identical galvanometers: Galvanometer Specifications: Resistance ( ) = 10 Ω Full-scale deflection current ( ) = 2 μA = 2 × 10⁻⁶ A Conversions:1. Voltmeter: One galvanometer is converted to measure up to 100 mV.2. Ammeter: The other is converted to measure up to 1 mA.These are used in an Ohm's law experiment with a resistor Ω and an ideal cell (no internal resistance initially).Later, the cell is replaced with one having an internal resistance of 5 Ω.We need to evaluate the correctness of the given statements (A, B, C, D).Step 1: Convert Galvanometer to Voltmeter Goal: Measure up to mV = 0.1 V. A voltmeter is created by adding a series resistor ( ) to the galvanometer.The total resistance ( ) should allow full-scale deflection at 0.1 V. Calculation: | | JEE Total Voltmeter Resistance ( RV): Statement B: Claims .Verdict: Incorrect (actual ).Step 2: Convert Galvanometer to Ammeter Goal: Measure up to mA = 0.001 A. An ammeter is created by adding a shunt resistor ( ) in parallel.The shunt diverts most of the current, allowing only μA through the galvanometer.Calculation: Total Ammeter Resistance ( ): Statement C: Claims .Verdict: Correct (rounded to 2 decimal places).Step 3: Measuring with Ideal Cell Circuit Setup: Voltmeter ( ) is placed in parallel with .Ammeter ( ) is placed in series.Effective Resistance of + Voltmeter: Total Circuit Resistance: Current Measurement: The ammeter reads the current through the entire circuit, but the voltmeter reads the voltage across , not just .Measured Resistance ( ): Statement A: Claims .Verdict: Correct (since falls in this range).Step 4: Effect of Internal Resistance ( ) When the cell has internal resistance: The total resistance increases to | | JEE The current decreases, but the voltmeter still measures the voltage across .Measured Resistance: Statement D: Claims Verdict: Incorrect (actual ).Final Answer Correct Statements: A and C.
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