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Ohm's Law is a fundamental principle in electronics and physics. It relates voltage (V), current (I), and resistance (R) in a circuit. The formula is expressed as \( V = IR \). This means that the voltage across a conductor is proportional to the product of the current flowing through it and its resistance.

In the context of the moving coil galvanometer exercise, Ohm's Law is used to determine the total resistance in the circuit when the galvanometer is converted into a voltmeter. Here, the current for full scale deflection is \( I_g = 0.005 \, \text{A} \) and the applied voltage is \( 5 \, \text{V} \). By rearranging the formula as \( R = \frac{V}{I} \), you can easily calculate total resistance. This law provides a simple way to relate the electrical variables and is pivotal for solving this exercise.

Galvanometer resistance refers to the intrinsic resistance within the coil of a galvanometer itself. This is the resistance that opposes the flow of current through the coil.

In this exercise, we are tasked with finding the resistance of the galvanometer \( R_g \). Galvanometers are sensitive instruments that require a small current to show full scale deflection. In the given problem, we found that the full scale occurs at \( 0.005 \, \text{A} \) current. By calculating the total resistance, using Ohm's Law, and subtracting the external resistance, the galvanometer's resistance was determined to be \( 25 \Omega \). This intrinsic resistance is crucial when calibrating or using galvanometers in different electrical circuits.

Full scale deflection is the point at which a measuring instrument, like a galvanometer, indicates the maximum scale reading. This is a critical factor for calibrating and understanding the operational limits of the instrument.

For a galvanometer, full scale deflection occurs at a specific current value—in this case, \( 0.005 \, \text{A} \). This means when the galvanometer reads its maximum, it only needs a small current, making it highly sensitive. Engineers and technicians use this full deflection current to ensure that the instrument is properly used within its prescribed limits, and when designing circuits in which these instruments will be employed. In this problem, the full scale deflection guides us on how much series resistance is to be added when turning the galvanometer into a voltmeter.

External resistance, also known as series resistance or multiplier, is the resistance added to a galvanometer when converting it to a voltmeter. Adding this resistance increases the potential range of measurements by reducing overall current sensitivity.

In this exercise, the external resistance is given as \( 975 \, \Omega \). This value is combined with the galvanometer's inherent resistance to make a complete voltmeter circuit, allowing it to measure up to \( 5 \, \text{V} \). External resistances are crucial in expanding the functionality of sensitive instruments, like galvanometers, allowing them to measure larger voltages without damaging the device or significantly impacting its accuracy. Understanding how to calculate and apply external resistances efficiently is key in electrical circuit design and instrumentation.