What is difference between emf and terminal potential difference of a cell?
2 Answers
The **EMF (Electromotive Force)** and the **Terminal Potential Difference** of a cell are both related to the voltage produced by a cell, but they differ based on the conditions of the circuit. Here's a detailed comparison:
### 1. **Electromotive Force (EMF)**:
- **Definition**: EMF is the total energy supplied by the cell per unit charge when no current is flowing through the circuit. It is the maximum potential difference between the two terminals of a cell when the circuit is open (no load).
- **Symbol**: Usually represented by \( \mathcal{E} \).
- **Cause**: EMF is caused by the chemical reactions occurring inside the cell, which separates charges and creates an electric potential.
- **Measurement**: EMF is measured when the cell is not connected to any external circuit (i.e., an open circuit). It represents the energy conversion capability of the cell.
- **Effect of Internal Resistance**: Since no current flows in an open circuit, the internal resistance of the cell does not affect the EMF.
- **Formula**: \( \mathcal{E} = V + Ir \)
- Where:
- \( V \) = terminal voltage (or potential difference)
- \( I \) = current
- \( r \) = internal resistance of the cell
### 2. **Terminal Potential Difference**:
- **Definition**: The terminal potential difference is the voltage across the terminals of the cell when current is flowing through the circuit (i.e., when the cell is connected to a load).
- **Symbol**: Often represented as \( V \).
- **Cause**: The terminal potential difference is lower than the EMF when the circuit is closed because of the internal resistance of the cell, which causes a drop in voltage as current flows through it.
- **Measurement**: It is measured when the circuit is closed (i.e., the cell is supplying current to the external load).
- **Effect of Internal Resistance**: As current flows, part of the EMF is used to overcome the cell's internal resistance, so the terminal potential difference is always less than the EMF.
- **Formula**: \( V = \mathcal{E} - Ir \)
- Where:
- \( V \) = terminal voltage
- \( \mathcal{E} \) = EMF of the cell
- \( I \) = current flowing through the circuit
- \( r \) = internal resistance of the cell
### Key Difference:
- **EMF**: Maximum voltage of a cell when no current is drawn (open circuit).
- **Terminal Potential Difference**: Voltage when the cell is supplying current (closed circuit), which is always less than the EMF due to internal resistance.
### Example:
Consider a cell with an EMF of 12 V and an internal resistance of 0.5 ohms. If a current of 2 A is drawn from the cell, the terminal potential difference would be:
\[ V = \mathcal{E} - Ir = 12 \, \text{V} - (2 \, \text{A} \times 0.5 \, \Omega) = 12 \, \text{V} - 1 \, \text{V} = 11 \, \text{V} \]
Here, the terminal voltage is 11 V, which is less than the EMF due to the voltage drop caused by the internal resistance.
In summary, the EMF is the ideal voltage of a cell, while the terminal potential difference is the actual voltage available when the cell is powering a circuit.
### 1. **Electromotive Force (EMF)**:
- **Definition**: EMF is the total energy supplied by the cell per unit charge when no current is flowing through the circuit. It is the maximum potential difference between the two terminals of a cell when the circuit is open (no load).
- **Symbol**: Usually represented by \( \mathcal{E} \).
- **Cause**: EMF is caused by the chemical reactions occurring inside the cell, which separates charges and creates an electric potential.
- **Measurement**: EMF is measured when the cell is not connected to any external circuit (i.e., an open circuit). It represents the energy conversion capability of the cell.
- **Effect of Internal Resistance**: Since no current flows in an open circuit, the internal resistance of the cell does not affect the EMF.
- **Formula**: \( \mathcal{E} = V + Ir \)
- Where:
- \( V \) = terminal voltage (or potential difference)
- \( I \) = current
- \( r \) = internal resistance of the cell
### 2. **Terminal Potential Difference**:
- **Definition**: The terminal potential difference is the voltage across the terminals of the cell when current is flowing through the circuit (i.e., when the cell is connected to a load).
- **Symbol**: Often represented as \( V \).
- **Cause**: The terminal potential difference is lower than the EMF when the circuit is closed because of the internal resistance of the cell, which causes a drop in voltage as current flows through it.
- **Measurement**: It is measured when the circuit is closed (i.e., the cell is supplying current to the external load).
- **Effect of Internal Resistance**: As current flows, part of the EMF is used to overcome the cell's internal resistance, so the terminal potential difference is always less than the EMF.
- **Formula**: \( V = \mathcal{E} - Ir \)
- Where:
- \( V \) = terminal voltage
- \( \mathcal{E} \) = EMF of the cell
- \( I \) = current flowing through the circuit
- \( r \) = internal resistance of the cell
### Key Difference:
- **EMF**: Maximum voltage of a cell when no current is drawn (open circuit).
- **Terminal Potential Difference**: Voltage when the cell is supplying current (closed circuit), which is always less than the EMF due to internal resistance.
### Example:
Consider a cell with an EMF of 12 V and an internal resistance of 0.5 ohms. If a current of 2 A is drawn from the cell, the terminal potential difference would be:
\[ V = \mathcal{E} - Ir = 12 \, \text{V} - (2 \, \text{A} \times 0.5 \, \Omega) = 12 \, \text{V} - 1 \, \text{V} = 11 \, \text{V} \]
Here, the terminal voltage is 11 V, which is less than the EMF due to the voltage drop caused by the internal resistance.
In summary, the EMF is the ideal voltage of a cell, while the terminal potential difference is the actual voltage available when the cell is powering a circuit.
The terms **electromotive force (EMF)** and **terminal potential difference** are often used in the context of electrical circuits, and though they are related, they describe different concepts. Here's a detailed explanation of each and their differences:
### Electromotive Force (EMF)
**Electromotive Force (EMF)** is a measure of the energy provided by a cell or battery per unit charge as it moves through the external circuit. It represents the maximum potential difference between the terminals of the cell when no current is flowing.
**Key Points:**
1. **Definition:** EMF is the work done per unit charge by the source (like a battery or generator) to move charges from one terminal to the other inside the cell.
2. **Unit:** The unit of EMF is volts (V).
3. **Internal Mechanism:** It reflects the internal energy conversion process within the cell, such as chemical energy to electrical energy in a battery.
4. **No Current Flow:** The EMF is defined when no current is flowing in the circuit (open-circuit condition). This is the maximum potential difference that the cell can provide.
### Terminal Potential Difference
**Terminal Potential Difference** (often just called **potential difference**) is the voltage across the terminals of a cell when it is connected to an external circuit and current is flowing.
**Key Points:**
1. **Definition:** The terminal potential difference is the actual voltage measured across the terminals of the cell when it is in use. It is the voltage available to the external circuit.
2. **Unit:** Like EMF, the terminal potential difference is also measured in volts (V).
3. **Internal Resistance:** The terminal potential difference is less than the EMF because it accounts for the internal resistance of the cell. When current flows, there is a voltage drop within the cell due to its internal resistance.
4. **Current Flow:** This potential difference is measured under load conditions, i.e., when the cell is part of a circuit and current is flowing.
### Difference Between EMF and Terminal Potential Difference
The primary difference between EMF and terminal potential difference lies in their conditions and the impact of internal resistance:
1. **Internal Resistance Effect:**
- **EMF:** This is the theoretical maximum voltage provided by the cell when no current is flowing, so internal resistance does not affect it.
- **Terminal Potential Difference:** When current flows, the internal resistance of the cell causes a drop in voltage, so the terminal potential difference is less than the EMF. The relationship is given by \( V = E - Ir \), where \( E \) is the EMF, \( I \) is the current, and \( r \) is the internal resistance of the cell.
2. **Measurement Condition:**
- **EMF:** Measured when the cell is not connected to any external circuit (open circuit).
- **Terminal Potential Difference:** Measured when the cell is connected to an external circuit and current is flowing.
3. **Practical Implications:**
- **EMF:** Represents the cell's ability to provide energy.
- **Terminal Potential Difference:** Represents the actual voltage available to the circuit and is what is used in practical applications.
In summary, EMF is the maximum voltage a cell can provide, while the terminal potential difference is the actual voltage available to an external circuit when current is flowing, and it is always less than the EMF due to internal resistance.
### Electromotive Force (EMF)
**Electromotive Force (EMF)** is a measure of the energy provided by a cell or battery per unit charge as it moves through the external circuit. It represents the maximum potential difference between the terminals of the cell when no current is flowing.
**Key Points:**
1. **Definition:** EMF is the work done per unit charge by the source (like a battery or generator) to move charges from one terminal to the other inside the cell.
2. **Unit:** The unit of EMF is volts (V).
3. **Internal Mechanism:** It reflects the internal energy conversion process within the cell, such as chemical energy to electrical energy in a battery.
4. **No Current Flow:** The EMF is defined when no current is flowing in the circuit (open-circuit condition). This is the maximum potential difference that the cell can provide.
### Terminal Potential Difference
**Terminal Potential Difference** (often just called **potential difference**) is the voltage across the terminals of a cell when it is connected to an external circuit and current is flowing.
**Key Points:**
1. **Definition:** The terminal potential difference is the actual voltage measured across the terminals of the cell when it is in use. It is the voltage available to the external circuit.
2. **Unit:** Like EMF, the terminal potential difference is also measured in volts (V).
3. **Internal Resistance:** The terminal potential difference is less than the EMF because it accounts for the internal resistance of the cell. When current flows, there is a voltage drop within the cell due to its internal resistance.
4. **Current Flow:** This potential difference is measured under load conditions, i.e., when the cell is part of a circuit and current is flowing.
### Difference Between EMF and Terminal Potential Difference
The primary difference between EMF and terminal potential difference lies in their conditions and the impact of internal resistance:
1. **Internal Resistance Effect:**
- **EMF:** This is the theoretical maximum voltage provided by the cell when no current is flowing, so internal resistance does not affect it.
- **Terminal Potential Difference:** When current flows, the internal resistance of the cell causes a drop in voltage, so the terminal potential difference is less than the EMF. The relationship is given by \( V = E - Ir \), where \( E \) is the EMF, \( I \) is the current, and \( r \) is the internal resistance of the cell.
2. **Measurement Condition:**
- **EMF:** Measured when the cell is not connected to any external circuit (open circuit).
- **Terminal Potential Difference:** Measured when the cell is connected to an external circuit and current is flowing.
3. **Practical Implications:**
- **EMF:** Represents the cell's ability to provide energy.
- **Terminal Potential Difference:** Represents the actual voltage available to the circuit and is what is used in practical applications.
In summary, EMF is the maximum voltage a cell can provide, while the terminal potential difference is the actual voltage available to an external circuit when current is flowing, and it is always less than the EMF due to internal resistance.