Short Answer

The sensitivity of a galvanometer refers to how well it can detect very small electric currents. A galvanometer is said to be sensitive if it shows a large deflection even when a tiny current flows through its coil. Higher sensitivity means the pointer moves more for a small input current.

A sensitive galvanometer is very useful in laboratory experiments because it helps measure weak currents accurately. Sensitivity can be increased by using more turns in the coil, a strong magnetic field, a light coil, and a soft spring.

Detailed Explanation

Sensitivity of galvanometer

The sensitivity of a galvanometer is an important property that describes how effectively the instrument can detect and measure very small currents. When an electric current passes through the coil of a galvanometer, the coil experiences a turning effect due to the magnetic field. This turning effect causes the pointer to move on the scale. The degree of movement or deflection for a given current determines how sensitive the instrument is.

A galvanometer with high sensitivity will show a large deflection even when a very small current is passed through it. On the other hand, if the pointer moves only slightly for the same small current, the galvanometer is less sensitive. Thus, sensitivity helps in understanding the quality and effectiveness of the galvanometer in measuring weak electric signals.

Definition of sensitivity

The sensitivity of a galvanometer can be defined as:

“The ability of a galvanometer to produce a large deflection for a small current flowing through it.”

In simple words, greater the deflection for a smaller current → greater the sensitivity.

Mathematically, sensitivity is often expressed as:

Current sensitivity = Deflection per unit current

If a galvanometer gives 1 division deflection for 1 microampere, it is more sensitive than another that gives 1 division for 5 microamperes.

Importance of galvanometer sensitivity

The sensitivity of a galvanometer is important for the following reasons:

1. Accurate measurement of small currents
   High sensitivity helps detect weak signals that cannot be measured by ordinary meters.
2. Use in laboratory experiments
   Sensitive galvanometers are used in physics experiments such as bridges, potentiometers, and induction studies.
3. Conversion into measuring instruments
   A sensitive galvanometer can be converted into an accurate ammeter or voltmeter with proper adjustments.
4. Improved detection of changes
   Even minute variations in current can be noticed by a sensitive instrument.

Factors affecting sensitivity of a galvanometer

Several physical and design parameters influence the sensitivity:

1. Number of turns in the coil

More turns mean stronger magnetic interaction, which increases the torque acting on the coil. This results in more deflection for the same current, thus increasing sensitivity.

2. Strength of the magnetic field

A strong magnetic field provides greater force on the current-carrying coil. This increases the deflection and improves sensitivity. Permanent magnets of high strength are usually used.

3. Area of the coil

A larger coil area means that the magnetic force acts on a bigger region, producing more torque. This makes the galvanometer more responsive to small currents.

4. Thickness of the coil wire

Thinner wires allow more turns to be wound in the coil, thereby increasing sensitivity. However, very thin wires are delicate and must be handled carefully.

5. Mass of the coil

A lighter coil has less inertia, so it rotates easily. This helps in achieving greater deflection with small currents.

6. Restoring torque of spring

A soft and flexible spring produces smaller restoring force. This allows the coil to deflect more for a given current, increasing sensitivity. A stiff spring reduces sensitivity.

Ways to increase the sensitivity

Engineers increase the sensitivity of galvanometers by:

• Increasing the number of wire turns
• Using a strong horseshoe magnet
• Increasing coil area
• Using soft springs
• Keeping the coil lightweight
• Ensuring frictionless movement of the coil

These changes help achieve higher accuracy and better performance.

Limitations of very high sensitivity

While high sensitivity is desirable, excessively sensitive galvanometers have disadvantages:

• They can be easily damaged by slightly large currents
• They may respond to unwanted vibrations
• External magnetic fields may cause false readings
• Temperature variations may affect spring tension

Therefore, a balance between sensitivity and durability is maintained.

Applications of sensitive galvanometers

• Used in Wheatstone bridge for null point detection
• Essential in potentiometer experiments
• Helps measure small induced currents
• Used in calibration of ammeters and voltmeters

Sensitive galvanometers allow precise electrical measurements, which are very important in physics and engineering.

Conclusion

The sensitivity of a galvanometer is its ability to show a large pointer deflection even for a very small current. It is an important property that determines how accurately the galvanometer can detect weak electrical signals. Sensitivity increases when the coil has more turns, the magnetic field is strong, the coil is light, and the spring is soft. A highly sensitive galvanometer is very useful in scientific experiments and electrical measurements, although excessive sensitivity must be controlled to avoid damage or incorrect readings.