What is galvanometer and how it is converted into ammeter and voltmeter?
2 Answers
A galvanometer is an instrument used to detect and measure small electric currents by creating a deflection of a needle or pointer. It operates based on the principle that a current-carrying coil in a magnetic field experiences a force, causing it to move. Here’s a more detailed breakdown of its operation and how it can be adapted into an ammeter or voltmeter:
### Galvanometer
**1. Working Principle:**
- **Electromagnetic Force:** When a current flows through the coil of a galvanometer, it creates a magnetic field. This field interacts with the field of a permanent magnet, producing a torque that causes the coil (and attached needle) to rotate.
- **Measurement:** The amount of rotation (or deflection) of the needle is proportional to the current passing through the coil. This deflection is read off a scale to determine the current.
**2. Components:**
- **Coil:** A coil of wire that carries the current.
- **Magnet:** Provides a constant magnetic field.
- **Pointer/Needle:** Attached to the coil, it moves in response to the electromagnetic force.
- **Scale:** Indicates the amount of current based on the needle's position.
### Converting a Galvanometer into an Ammeter
An ammeter measures the current flowing through a circuit. To convert a galvanometer into an ammeter:
**1. Shunt Resistor:**
- **Purpose:** A shunt resistor is placed in parallel with the galvanometer to bypass most of the current. The shunt allows the bulk of the current to flow through it while only a small, measurable portion flows through the galvanometer.
- **Selection:** The value of the shunt resistor is chosen based on the maximum current you want to measure and the full-scale deflection of the galvanometer. The formula for the shunt resistor is:
\[
R_{\text{shunt}} = \frac{V_{\text{g}}}{I_{\text{full scale}} - I_{\text{g}}}
\]
where \( V_{\text{g}} \) is the voltage across the galvanometer coil (which is small), \( I_{\text{full scale}} \) is the maximum current the ammeter should measure, and \( I_{\text{g}} \) is the current that causes full-scale deflection of the galvanometer.
**2. Calibration:**
- **Adjustments:** Once the shunt resistor is installed, the galvanometer is calibrated so that its full-scale deflection corresponds to the maximum current the ammeter is designed to measure.
### Converting a Galvanometer into a Voltmeter
A voltmeter measures the potential difference between two points in a circuit. To convert a galvanometer into a voltmeter:
**1. Series Resistor (Multiplying Resistor):**
- **Purpose:** A high resistance (series resistor) is added to the galvanometer to limit the current flowing through it, allowing it to measure a higher voltage without damaging the instrument.
- **Selection:** The value of this resistor is chosen based on the maximum voltage you want to measure and the current required for full-scale deflection of the galvanometer. The formula for the series resistor is:
\[
R_{\text{series}} = \frac{V_{\text{full scale}}}{I_{\text{g}}}
\]
where \( V_{\text{full scale}} \) is the maximum voltage the voltmeter should measure, and \( I_{\text{g}} \) is the current for full-scale deflection.
**2. Calibration:**
- **Adjustments:** After installing the series resistor, the galvanometer is calibrated so that the full-scale deflection corresponds to the full-scale voltage measurement.
### Summary
- **Galvanometer:** Measures small currents via needle deflection.
- **Ammeter:** Uses a parallel shunt resistor to measure larger currents.
- **Voltmeter:** Uses a series resistor to measure voltages.
Each conversion involves adding appropriate resistors to modify the range and function of the galvanometer, allowing it to serve different measurement purposes in electrical circuits.
### Galvanometer
**1. Working Principle:**
- **Electromagnetic Force:** When a current flows through the coil of a galvanometer, it creates a magnetic field. This field interacts with the field of a permanent magnet, producing a torque that causes the coil (and attached needle) to rotate.
- **Measurement:** The amount of rotation (or deflection) of the needle is proportional to the current passing through the coil. This deflection is read off a scale to determine the current.
**2. Components:**
- **Coil:** A coil of wire that carries the current.
- **Magnet:** Provides a constant magnetic field.
- **Pointer/Needle:** Attached to the coil, it moves in response to the electromagnetic force.
- **Scale:** Indicates the amount of current based on the needle's position.
### Converting a Galvanometer into an Ammeter
An ammeter measures the current flowing through a circuit. To convert a galvanometer into an ammeter:
**1. Shunt Resistor:**
- **Purpose:** A shunt resistor is placed in parallel with the galvanometer to bypass most of the current. The shunt allows the bulk of the current to flow through it while only a small, measurable portion flows through the galvanometer.
- **Selection:** The value of the shunt resistor is chosen based on the maximum current you want to measure and the full-scale deflection of the galvanometer. The formula for the shunt resistor is:
\[
R_{\text{shunt}} = \frac{V_{\text{g}}}{I_{\text{full scale}} - I_{\text{g}}}
\]
where \( V_{\text{g}} \) is the voltage across the galvanometer coil (which is small), \( I_{\text{full scale}} \) is the maximum current the ammeter should measure, and \( I_{\text{g}} \) is the current that causes full-scale deflection of the galvanometer.
**2. Calibration:**
- **Adjustments:** Once the shunt resistor is installed, the galvanometer is calibrated so that its full-scale deflection corresponds to the maximum current the ammeter is designed to measure.
### Converting a Galvanometer into a Voltmeter
A voltmeter measures the potential difference between two points in a circuit. To convert a galvanometer into a voltmeter:
**1. Series Resistor (Multiplying Resistor):**
- **Purpose:** A high resistance (series resistor) is added to the galvanometer to limit the current flowing through it, allowing it to measure a higher voltage without damaging the instrument.
- **Selection:** The value of this resistor is chosen based on the maximum voltage you want to measure and the current required for full-scale deflection of the galvanometer. The formula for the series resistor is:
\[
R_{\text{series}} = \frac{V_{\text{full scale}}}{I_{\text{g}}}
\]
where \( V_{\text{full scale}} \) is the maximum voltage the voltmeter should measure, and \( I_{\text{g}} \) is the current for full-scale deflection.
**2. Calibration:**
- **Adjustments:** After installing the series resistor, the galvanometer is calibrated so that the full-scale deflection corresponds to the full-scale voltage measurement.
### Summary
- **Galvanometer:** Measures small currents via needle deflection.
- **Ammeter:** Uses a parallel shunt resistor to measure larger currents.
- **Voltmeter:** Uses a series resistor to measure voltages.
Each conversion involves adding appropriate resistors to modify the range and function of the galvanometer, allowing it to serve different measurement purposes in electrical circuits.
A **galvanometer** is an electromechanical device used to detect and measure small electric currents. It works based on the principle that a current-carrying conductor experiences a force when placed in a magnetic field, which causes a needle to move, giving a proportional indication of the current.
### Conversion of a Galvanometer into an Ammeter
An **ammeter** is used to measure larger currents in a circuit, and to convert a galvanometer into an ammeter, a **shunt resistor** (a low resistance) is connected in **parallel** with the galvanometer. This allows most of the current to bypass the galvanometer so that the sensitive galvanometer coil is not damaged by high currents.
#### Steps:
1. **Shunt Resistor Calculation**:
- If \( I \) is the total current to be measured, \( I_g \) is the current required for full-scale deflection of the galvanometer, and \( R_g \) is the resistance of the galvanometer, the shunt resistance \( R_s \) can be calculated using:
\[
R_s = \frac{I_g \cdot R_g}{I - I_g}
\]
The shunt resistor allows the extra current \( (I - I_g) \) to pass through it, while only \( I_g \) flows through the galvanometer.
2. **Parallel Configuration**:
- The shunt resistor is connected across the terminals of the galvanometer, thereby dividing the current between the galvanometer and the shunt resistor, with most of the current flowing through the low-resistance shunt.
3. **Result**:
- The galvanometer is now able to measure higher currents because the shunt resistor limits the current passing through it to only what is needed for full-scale deflection.
### Conversion of a Galvanometer into a Voltmeter
A **voltmeter** is used to measure potential difference (voltage) across two points in a circuit. To convert a galvanometer into a voltmeter, a **series resistor** (a high resistance) is connected in **series** with the galvanometer. This limits the current flowing through the galvanometer, allowing it to measure the voltage across the circuit.
#### Steps:
1. **Series Resistor Calculation**:
- If \( V \) is the voltage to be measured, \( I_g \) is the full-scale deflection current of the galvanometer, and \( R_g \) is the resistance of the galvanometer, the series resistance \( R_s \) can be calculated using:
\[
R_s = \frac{V}{I_g} - R_g
\]
The series resistor ensures that the current through the galvanometer remains below the full-scale deflection value, even at higher voltages.
2. **Series Configuration**:
- The series resistor is connected in line with the galvanometer. This setup reduces the current through the galvanometer to a safe value, allowing it to measure voltage.
3. **Result**:
- The galvanometer, with the added series resistance, is now capable of measuring the voltage across a given portion of the circuit, functioning as a voltmeter.
### Summary:
- **Galvanometer to Ammeter**: Add a low resistance (shunt) in parallel.
- **Galvanometer to Voltmeter**: Add a high resistance (series) in series.
These modifications allow the galvanometer to measure larger currents (as an ammeter) or voltages (as a voltmeter) by altering the amount of current flowing through it.
### Conversion of a Galvanometer into an Ammeter
An **ammeter** is used to measure larger currents in a circuit, and to convert a galvanometer into an ammeter, a **shunt resistor** (a low resistance) is connected in **parallel** with the galvanometer. This allows most of the current to bypass the galvanometer so that the sensitive galvanometer coil is not damaged by high currents.
#### Steps:
1. **Shunt Resistor Calculation**:
- If \( I \) is the total current to be measured, \( I_g \) is the current required for full-scale deflection of the galvanometer, and \( R_g \) is the resistance of the galvanometer, the shunt resistance \( R_s \) can be calculated using:
\[
R_s = \frac{I_g \cdot R_g}{I - I_g}
\]
The shunt resistor allows the extra current \( (I - I_g) \) to pass through it, while only \( I_g \) flows through the galvanometer.
2. **Parallel Configuration**:
- The shunt resistor is connected across the terminals of the galvanometer, thereby dividing the current between the galvanometer and the shunt resistor, with most of the current flowing through the low-resistance shunt.
3. **Result**:
- The galvanometer is now able to measure higher currents because the shunt resistor limits the current passing through it to only what is needed for full-scale deflection.
### Conversion of a Galvanometer into a Voltmeter
A **voltmeter** is used to measure potential difference (voltage) across two points in a circuit. To convert a galvanometer into a voltmeter, a **series resistor** (a high resistance) is connected in **series** with the galvanometer. This limits the current flowing through the galvanometer, allowing it to measure the voltage across the circuit.
#### Steps:
1. **Series Resistor Calculation**:
- If \( V \) is the voltage to be measured, \( I_g \) is the full-scale deflection current of the galvanometer, and \( R_g \) is the resistance of the galvanometer, the series resistance \( R_s \) can be calculated using:
\[
R_s = \frac{V}{I_g} - R_g
\]
The series resistor ensures that the current through the galvanometer remains below the full-scale deflection value, even at higher voltages.
2. **Series Configuration**:
- The series resistor is connected in line with the galvanometer. This setup reduces the current through the galvanometer to a safe value, allowing it to measure voltage.
3. **Result**:
- The galvanometer, with the added series resistance, is now capable of measuring the voltage across a given portion of the circuit, functioning as a voltmeter.
### Summary:
- **Galvanometer to Ammeter**: Add a low resistance (shunt) in parallel.
- **Galvanometer to Voltmeter**: Add a high resistance (series) in series.
These modifications allow the galvanometer to measure larger currents (as an ammeter) or voltages (as a voltmeter) by altering the amount of current flowing through it.