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Ch. 26 - DC Circuits
Giancoli Douglas - Physics for Scientists and Engineers 5th edition
Giancoli Douglas5th editionPhysics for Scientists and EngineersISBN: 9780137488179Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoGiancoli Douglas 5th editionCh. 26 - DC CircuitsProblema 58b
Capitolo 25, Problema 58b

A galvanometer has an internal resistance of 32 Ω and deflects full scale for a 48-μA current. Describe how to use this galvanometer to make a voltmeter to give a full scale deflection of 250 V.

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Determine the total resistance required for the voltmeter to give a full-scale deflection at 250 V. Using Ohm's Law, the total resistance R_total is given by: Rtotal=VI, where V = 250 V and I = 48 μA.
Calculate the resistance that needs to be added in series with the galvanometer. The total resistance of the voltmeter is the sum of the internal resistance of the galvanometer (R_g = 32 Ω) and the series resistance (R_s). Therefore, Rs=Rtotal-Rg.
Substitute the values of R_total and R_g into the equation to find R_s. This will give the resistance that must be added in series with the galvanometer to create the desired voltmeter.
Connect the calculated series resistance (R_s) in series with the galvanometer. This configuration ensures that the galvanometer will deflect full scale when the voltage across the entire circuit is 250 V.
Verify the setup by checking that the total resistance of the voltmeter matches the calculated R_total and that the galvanometer deflects full scale at 250 V.

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Galvanometer

A galvanometer is an electromechanical device used to detect and measure small electric currents. It operates by using a coil of wire that experiences a magnetic field, causing it to rotate and indicate the current level on a scale. The full-scale deflection indicates the maximum current the galvanometer can measure, which is crucial for converting it into other measuring instruments.

Internal Resistance

Internal resistance refers to the resistance within a device, such as a galvanometer, that opposes the flow of current. In this context, the internal resistance of 32 Ω affects how the galvanometer interacts with external circuits. Understanding this resistance is essential for calculating how to connect the galvanometer to measure higher voltages without damaging it.
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Voltage Divider

A voltage divider is a simple circuit that uses resistors to produce a lower voltage from a higher voltage source. By adding a series resistor to the galvanometer, the voltage across the galvanometer can be controlled, allowing it to measure higher voltages without exceeding its full-scale deflection. This principle is key to converting the galvanometer into a voltmeter capable of measuring up to 250 V.
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