Detecting Current: Connect the galvanometer in series with the component being tested. If the needle moves from the center, current is present; the direction of movement indicates the direction of current flow.
Finding the Null Point: In bridge or potentiometer circuits, move a sliding contact (jockey) along a resistance wire until the galvanometer shows zero deflection. This indicates that the potential at the contact point matches the potential of the source being measured.
Increasing Sensitivity: Sensitivity can be improved by increasing the number of turns in the coil, using a stronger permanent magnet, or using a spring with a lower torsional constant. However, these changes must be balanced against the physical size and durability of the instrument.
| Feature | Galvanometer | Ammeter | Voltmeter |
|---|---|---|---|
| Primary Use | Detects small currents and null points | Measures large currents | Measures potential difference |
| Resistance | Moderate internal resistance | Very low resistance | Very high resistance |
| Scale | Zero is usually at the center | Zero is at the far left | Zero is at the far left |
| Connection | Series (for detection) | Series (for measurement) | Parallel (across components) |
Check for Null Deflection: In potentiometer problems, always look for the condition where the galvanometer current is zero. This simplifies the circuit as you can treat the galvanometer branch as an open circuit for potential calculations.
Directional Analysis: Remember that the direction of deflection tells you which way the current is flowing. If the needle moves right, the potential at the positive terminal is higher than the negative; if it moves left, the reverse is true.
Sensitivity Limits: Be aware that galvanometers are delicate. In practical exam scenarios, always start with a high-value protective resistor in series to prevent the coil from burning out due to excessive current before the null point is found.
