How Does a Galvanometer Differ from an Ammeter in Working Principle and Use?
Comparing the Difference Between Galvanometer and Ammeter is academically important for understanding how electric currents are detected and measured in circuits. Grasping their distinctions aids students in circuit analysis, experiment design, and clear application of measurement devices in physics and mathematics studies.
Mathematical Meaning of Galvanometer
A galvanometer is an instrument used to detect and measure small electric currents in an electric circuit. It indicates both the presence and direction of current flow through needle deflection.
The galvanometer’s operation is based on the torque experienced by a current-carrying coil placed in a magnetic field. This torque causes deflection proportional to the current.
$ \tau = N I A B \sin\theta $
In most arrangements, the coil is suspended in a radial magnetic field, making $ \sin\theta = 1 $, ensuring linear proportionality between current and deflection. For related concepts, refer to Difference Between Cell Potential And Emf.
Understanding Ammeter in Electrical Circuits
An ammeter measures the magnitude of electric current in a circuit. It is designed to be connected in series and indicates current in amperes with high accuracy.
Ammeters possess very low internal resistance to minimize voltage drop, ensuring that their insertion does not alter the circuit current significantly.
An ammeter is generally constructed by placing a low-resistance shunt in parallel with a galvanometer. This enables the device to measure larger currents. For additional comparison of measurement devices, see Difference Between Ammeter And Voltmeter.
Comparative View of Galvanometer and Ammeter
| Galvanometer | Ammeter |
|---|---|
| Detects and measures small currents | Measures current of larger magnitude |
| Shows direction and magnitude of current | Shows only magnitude of current |
| Moderate to high internal resistance | Very low internal resistance |
| Sensitive to small currents | Less sensitive, designed for higher currents |
| Scale can be positive and negative | Scale is only positive (current only) |
| Used in null point and bridge experiments | Used for direct measurement in circuits |
| Connected in series for small current detection | Connected in series to measure circuit current |
| Measures current in microampere or milliampere | Measures current in amperes |
| Can be converted to ammeter with a shunt | Constructed using galvanometer and shunt |
| Deflection proportional to current | Deflection directly calibrated in amperes |
| Primarily for laboratory experiments | Used in practical and industrial applications |
| Can detect reversal of current direction | Cannot detect direction, only magnitude |
| Operates with weak currents | Operates with larger currents |
| Sensitive to both AC and DC (with modifications) | More commonly used for DC, but AC variants exist |
| Used to identify circuit faults at low currents | Used to monitor overall current consumption |
| Analog or digital types available | Analog or digital types available |
| Typically not built for direct AC measurement | Special ammeters designed for both DC and AC |
| Part of measurement bridges or potentiometers | Placed in main current path of appliances |
| Scale may need calibration for quantitative reading | Scale is calibrated; direct reading possible |
| Usually more delicate, highly sensitive | Rugged, suitable for routine measurement |
Core Distinctions Between Galvanometer and Ammeter
- Galvanometer detects small currents; ammeter measures large currents
- Galvanometer shows current direction; ammeter shows only magnitude
- Ammeter has low resistance; galvanometer has moderate resistance
- Galvanometer is more sensitive to weak currents
- Ammeter gives direct ampere reading; galvanometer shows deflection
Illustrative Examples: Galvanometer and Ammeter
If a galvanometer gives a full-scale deflection for 1 mA, it can detect current flow and its reversal. When combined with a 0.1 Ω shunt, it can be used as an ammeter to measure up to 1 A.
If a circuit current is 0.8 A, an ammeter connected in series will directly show a reading close to 0.8 on its calibrated scale.
Where These Concepts Are Used
- Galvanometer used for detecting current in bridge circuits
- Ammeter used for measuring main current in electric circuits
- Galvanometer enables study of current direction in experiments
- Ammeter helps check safe current levels in appliances
- Both are used for educational laboratory measurements
Concise Comparison
In simple words, a galvanometer detects and measures small currents with direction sensitivity, whereas an ammeter measures the magnitude of larger currents with high accuracy.
FAQs on What Is the Difference Between a Galvanometer and an Ammeter?
1. What is the difference between a galvanometer and an ammeter?
Galvanometers are sensitive instruments that detect and measure small electric currents, while ammeters are used to measure larger currents in a circuit.
Key differences:
- Galvanometer: Measures small currents; can detect direction of current; highly sensitive.
- Ammeter: Measures larger currents; direction seldom matters; less sensitive because it is designed to carry higher currents.
- Conversion: Galvanometers can be converted into ammeters by placing a low resistance (shunt) in parallel.
- Usage: Galvanometer is mainly for laboratory use; ammeter is used in practical circuits.
2. How can a galvanometer be converted into an ammeter?
A galvanometer can be converted into an ammeter by connecting a low resistance (shunt) in parallel with it.
Steps:
- Calculate required shunt resistance based on desired current range.
- Connect shunt resistance in parallel to galvanometer coil.
- This allows most of the current to bypass the galvanometer, enabling measurement of higher currents without damaging the instrument.
3. Why can't a galvanometer be used directly as an ammeter?
A galvanometer cannot be used directly as an ammeter because it is designed for very small currents and would get damaged or give inaccurate readings for larger currents.
- Galvanometer's coil has high resistance and low current capacity.
- Passing large currents can burn the coil or cause deflection errors.
- Direct measurement of strong currents requires low resistance and robust structure—features of an ammeter.
4. What is the working principle of a galvanometer?
A galvanometer works on the principle that a current-carrying coil placed in a magnetic field experiences a torque, causing the coil to rotate, indicating the presence and magnitude of current.
- The deflection is proportional to the current passing through the coil.
- Direction of deflection shows direction of current.
5. What is the main function of an ammeter?
The main function of an ammeter is to measure the magnitude of electric current flowing through a circuit.
- It measures current in amperes.
- Must be connected in series with the circuit.
- Has very low resistance so it does not affect circuit current.
6. List two key differences between a galvanometer and an ammeter.
The differences between a galvanometer and an ammeter are:
- Galvanometer: Sensitive; measures small currents; shows direction.
- Ammeter: Measures larger currents; less sensitive; generally does not show direction.
7. What is a shunt and how is it used in galvanometers and ammeters?
Shunt is a low resistance connected in parallel with the galvanometer.
- It allows most of the current to pass through itself, protecting galvanometer from high currents.
- Enables the galvanometer to act as an ammeter for higher currents without damage.
- Ensures accurate measurement by diverting excess current.
8. Which instrument is more sensitive: galvanometer or ammeter?
Galvanometer is more sensitive than ammeter.
- It detects and measures very small currents, even microamperes.
- Ammeter is designed for higher currents and thus has lower sensitivity.
9. Why is an ammeter connected in series in a circuit?
An ammeter is always connected in series so that the entire current flows through it, enabling correct measurement of circuit current.
- Series connection ensures full current passes through the meter.
- Parallel connection may damage the instrument or give wrong readings.
10. State the similarities and differences between ammeter and galvanometer.
Both ammeter and galvanometer are devices for current measurement, but they differ in sensitivity and function.
- Similarities: Both measure electric current; operate on electromagnetic deflection.
- Differences: Galvanometer is more sensitive and measures small currents; ammeter measures larger currents and is less sensitive.
11. How does the resistance of a galvanometer compare to that of an ammeter?
A galvanometer has a relatively higher resistance compared to an ammeter, which is designed to have very low resistance to avoid altering the circuit's current flow.
12. Can a galvanometer measure both AC and DC current?
A typical galvanometer measures only direct current (DC) because its deflection depends on current direction. Specialized galvanometers (moving iron type) can measure alternating current (AC).
