Definition

Noun: A ballistic galvanometer is a sensitive electrical instrument designed to measure the total quantity of electric charge (or a short-duration current pulse) passing through it. Unlike standard galvanometers that measure steady current, it utilizes the mechanical inertia of its moving coil to capture the momentum imparted by a brief current flow, allowing the measurement of the charge integral.

Usage

The ballistic galvanometer is used in laboratory settings to measure electric charge or to calibrate other instruments by observing the maximum deflection ("throw") of its needle or coil, which is proportional to the total charge that passed through it. - The physicist used a ballistic galvanometer to determine the charge stored in the capacitor. - Accurate measurement of the photoelectric current required a sensitive ballistic galvanometer.

Advanced Usage

• Ballistic Constant: Each ballistic galvanometer has a specific ballistic constant (or charge sensitivity), which is the charge required to produce a unit scale deflection. This constant must be determined through calibration.
• Damping: Critical damping is often employed in a ballistic galvanometer to ensure the coil comes to rest quickly after its initial throw, allowing for an accurate reading of the maximum deflection.

Variants and Related Words

• Galvanometer (n): A general instrument for detecting and measuring small electric currents.
• Ballistic (adj): In physics, relating to the motion of a projectile or, by extension, to a sudden, impulsive action like the discharge measured by this instrument.

Synonyms

• Charge-measuring galvanometer
• Ballistic meter (less common)

Notes on Meaning

The term "ballistic" in ballistic galvanometer is analogous to ballistics, the study of projectiles. Here, it refers to the impulsive, "projectile-like" nature of the measurement where the initial velocity (or maximum displacement) of the coil's swing is used to deduce the total impulse (charge) that caused it. It does not measure current over time but the integral of current.

Noun

1. a moving-coil galvanometer that measures electric charge