An ammeter requires a change of 3 A in its coil to produce a change in deflection of the pointer by 12 mm. Its sensitivity is
4 mm/A
Understanding Ammeter Sensitivity
An ammeter is an instrument used to measure electric current. Its sensitivity tells us how much the pointer deflects for a given change in current. A more sensitive ammeter will show a larger deflection for a smaller change in current.
Mathematically, the sensitivity of an ammeter is defined as the ratio of the change in deflection of the pointer to the change in the current flowing through its coil.
We can write this relationship as:
\[ \text{Sensitivity} = \frac{\text{Change in deflection}}{\text{Change in current}} \]Calculating Ammeter Sensitivity
In this particular problem, we are given the following information:
- Change in current in the coil = 3 A
- Change in deflection of the pointer = 12 mm
Using the formula for sensitivity, we can substitute the given values:
\[ \text{Sensitivity} = \frac{12 \text{ mm}}{3 \text{ A}} \]Now, we perform the division:
\[ \text{Sensitivity} = 4 \text{ mm/A} \]This result means that for every 1 ampere change in current flowing through the ammeter's coil, the pointer deflects by 4 millimeters.
Summarizing the Calculation
| Quantity | Value | Unit |
|---|---|---|
| Change in Current (\(\Delta I\)) | 3 | A |
| Change in Deflection (\(\Delta \theta\)) | 12 | mm |
| Sensitivity (\(S = \frac{\Delta \theta}{\Delta I}\)) | \(\frac{12}{3} = 4\) | mm/A |
Therefore, the sensitivity of the ammeter is 4 mm/A.
Revision Table: Key Ammeter Concepts
| Concept | Definition | Unit (Example) |
|---|---|---|
| Ammeter | Instrument for measuring electric current in a circuit. | N/A |
| Sensitivity | Change in output (deflection) per unit change in input (current). | mm/A, degrees/A |
| Range | The maximum current an ammeter can measure. | A, mA |
| Internal Resistance | Resistance of the ammeter coil and shunt. Ideally zero for an ideal ammeter. | Ohms (\(\Omega\)) |
Additional Information on Ammeters and Sensitivity
Ammeter sensitivity is an important characteristic. A highly sensitive ammeter can detect and measure smaller currents accurately. The sensitivity of a moving-coil galvanometer (which forms the basis of many ammeters) depends on factors like the magnetic field strength, the number of turns in the coil, the area of the coil, and the suspension's torsional constant.
To convert a sensitive galvanometer into an ammeter, a low resistance shunt is connected in parallel with the galvanometer coil. The shunt allows most of the current to bypass the galvanometer, protecting it from damage and extending the range of measurement. The sensitivity calculated in this problem refers to the overall sensitivity of the instrument as a whole.
Units of sensitivity can vary depending on the output measurement. If deflection is measured in degrees, the sensitivity might be in degrees/ampere.
Important Questions from Sensitivity
During the measurement of voltage, the voltmeter responded with a 0.18-V change when the input was varied by 0.2 V. Find the sensitivity of the instrument.
- If the value of (1 + GH) is less than 1, then sensitivity is/has _____.
There are 2 systems:
a. An automatic washing machine
b. An automatic intensity adjustable light bulb
Which of these systems will be more sensitive to the variation in system's gain?
Study the given table for resistance values of a platinum thermometer measured at a range of temperatures. Calculate the sensitivity of the measurement of the instrument.
Resistance (Ω) Temperature (°C) 200 100 205 150 210 200 215 250 If meter A requires 100 mA to give full-scale deflection, meter B requires 50 mA to give scale deflection and meter C requires 80 mA to give full-scale deflection, then the
