A galvanometer is a sensitive device used to detect and measure small electric currents. It operates based on the principles of electromagnetism, particularly the interaction between an electric current and a magnetic field. Here’s how it works:
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Step 1: Current Creates Magnetic Field: Inside the galvanometer, there is a coil of wire placed within a magnetic field, usually produced by a permanent magnet. When an electric current flows through the coil, it generates its own magnetic field according to Ampère’s law.
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Step 2: Torque on the Coil: The magnetic field produced by the current interacts with the magnetic field of the permanent magnet. According to the Lorentz force law, this interaction exerts a torque on the coil. The torque causes the coil to rotate.
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Step 3: Deflection of the Needle: The coil is attached to a needle or pointer, which moves over a calibrated scale. The amount of deflection (how much the needle moves) is proportional to the amount of current flowing through the coil. The greater the current, the greater the deflection.
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Step 4: Zeroing and Calibration: Galvanometers are calibrated to measure very small currents. If there is no current flowing through the coil, the needle points to zero on the scale. When current flows, the needle moves away from the zero point in proportion to the strength of the current.
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Step 5: Use in Measuring Current: Galvanometers are often used to measure the magnitude of small currents in a circuit. For larger currents, a shunt resistor is placed in parallel with the galvanometer to prevent damage to the delicate instrument.