Why is terminal voltage sometimes less than the expected voltage of A battery?
2 Answers
The terminal voltage of a battery can be less than its expected voltage for several reasons:
1. **Internal Resistance**: All batteries have some internal resistance. When a load is connected, the current flowing through this internal resistance causes a voltage drop, reducing the terminal voltage.
2. **State of Charge**: If a battery is partially discharged, its terminal voltage can be lower than its rated voltage. As batteries discharge, their voltage typically decreases.
3. **Temperature Effects**: Temperature can influence battery performance. Colder temperatures can increase internal resistance and reduce the chemical reactions that generate voltage, leading to a lower terminal voltage.
4. **Load Conditions**: The amount of current drawn from the battery affects the terminal voltage. Higher loads result in greater voltage drops due to internal resistance.
5. **Battery Age and Health**: Older or damaged batteries may have increased internal resistance or degraded chemical components, resulting in lower terminal voltage.
6. **Electrolyte Concentration**: In certain types of batteries, changes in electrolyte concentration can affect voltage output, especially in lead-acid batteries.
Understanding these factors is important for effectively managing battery performance in practical applications.
1. **Internal Resistance**: All batteries have some internal resistance. When a load is connected, the current flowing through this internal resistance causes a voltage drop, reducing the terminal voltage.
2. **State of Charge**: If a battery is partially discharged, its terminal voltage can be lower than its rated voltage. As batteries discharge, their voltage typically decreases.
3. **Temperature Effects**: Temperature can influence battery performance. Colder temperatures can increase internal resistance and reduce the chemical reactions that generate voltage, leading to a lower terminal voltage.
4. **Load Conditions**: The amount of current drawn from the battery affects the terminal voltage. Higher loads result in greater voltage drops due to internal resistance.
5. **Battery Age and Health**: Older or damaged batteries may have increased internal resistance or degraded chemical components, resulting in lower terminal voltage.
6. **Electrolyte Concentration**: In certain types of batteries, changes in electrolyte concentration can affect voltage output, especially in lead-acid batteries.
Understanding these factors is important for effectively managing battery performance in practical applications.
The terminal voltage of a battery is sometimes less than the expected voltage (also known as the **electromotive force** or **emf**) due to the **internal resistance** of the battery. This internal resistance causes a voltage drop within the battery when a current flows through it. Let's break down this concept in detail to understand why this happens:
### 1. **Understanding Electromotive Force (emf) and Terminal Voltage:**
- **Electromotive Force (emf):** The emf of a battery is the maximum potential difference between its terminals when no current is flowing. It is the ideal voltage that the battery can provide, often labeled on the battery as its nominal voltage (e.g., 1.5V for a standard AA battery, 12V for a car battery).
- **Terminal Voltage:** The terminal voltage is the actual voltage measured across the battery terminals when a load is connected, and current is flowing. It can be less than the emf due to internal factors within the battery.
### 2. **Internal Resistance of a Battery:**
Every battery has an **internal resistance** (denoted as \( r_{\text{int}} \)) due to its internal chemical processes and material properties. This resistance opposes the flow of electric current within the battery itself. When a current \( I \) flows through the battery, the internal resistance causes a voltage drop given by Ohm's Law:
\[
V_{\text{drop}} = I \cdot r_{\text{int}}
\]
### 3. **Effect of Internal Resistance on Terminal Voltage:**
When a battery is under load (i.e., connected to a circuit and delivering current), the terminal voltage \( V_{\text{terminal}} \) is given by:
\[
V_{\text{terminal}} = \text{emf} - V_{\text{drop}}
\]
Substituting the voltage drop due to internal resistance, we get:
\[
V_{\text{terminal}} = \text{emf} - I \cdot r_{\text{int}}
\]
From this equation, it is clear that the terminal voltage is less than the emf when there is a current flowing through the battery. The greater the current, the greater the voltage drop, and hence the lower the terminal voltage.
### 4. **Factors Affecting the Internal Resistance:**
Several factors can affect the internal resistance of a battery:
- **Battery Type and Chemistry:** Different types of batteries (e.g., alkaline, lithium-ion, lead-acid) have different internal resistances due to their varying chemical compositions and designs.
- **Age of the Battery:** Over time, batteries tend to build up internal resistance due to chemical degradation, corrosion, and other factors, leading to a more significant voltage drop.
- **Temperature:** The internal resistance of a battery can change with temperature. Typically, resistance increases at low temperatures, causing a greater voltage drop in cold conditions.
- **State of Charge:** A battery's internal resistance can vary depending on its state of charge. As a battery discharges, its internal resistance may increase, further lowering the terminal voltage.
### 5. **Practical Implications:**
- When using a battery in a device, the voltage you measure across the terminals (the terminal voltage) will usually be lower than the labeled emf. This discrepancy becomes more pronounced under heavy loads (i.e., when the device draws a significant amount of current).
- If a device requires a specific operating voltage, the reduced terminal voltage can lead to malfunction or reduced performance. For example, a flashlight might dim, or an electronic device may not function correctly when the terminal voltage drops too low.
- This also explains why batteries have reduced efficiency at high currents or under heavy loads—more energy is lost internally as heat due to the internal resistance.
### 6. **Example Calculation:**
Consider a 12V battery with an internal resistance of 0.5 ohms. If a device connected to the battery draws a current of 2 amperes, the terminal voltage can be calculated as:
\[
V_{\text{drop}} = I \cdot r_{\text{int}} = 2 \, \text{A} \times 0.5 \, \Omega = 1 \, \text{V}
\]
Therefore, the terminal voltage is:
\[
V_{\text{terminal}} = 12 \, \text{V} - 1 \, \text{V} = 11 \, \text{V}
\]
As shown, the terminal voltage is less than the emf of the battery due to the voltage drop across its internal resistance.
### 7. **Conclusion:**
The terminal voltage of a battery is often less than its emf due to the internal resistance of the battery. When current flows, this internal resistance causes a voltage drop, reducing the terminal voltage. This effect becomes more pronounced with increased current, aging batteries, or under certain environmental conditions, impacting the performance of devices powered by the battery.
### 1. **Understanding Electromotive Force (emf) and Terminal Voltage:**
- **Electromotive Force (emf):** The emf of a battery is the maximum potential difference between its terminals when no current is flowing. It is the ideal voltage that the battery can provide, often labeled on the battery as its nominal voltage (e.g., 1.5V for a standard AA battery, 12V for a car battery).
- **Terminal Voltage:** The terminal voltage is the actual voltage measured across the battery terminals when a load is connected, and current is flowing. It can be less than the emf due to internal factors within the battery.
### 2. **Internal Resistance of a Battery:**
Every battery has an **internal resistance** (denoted as \( r_{\text{int}} \)) due to its internal chemical processes and material properties. This resistance opposes the flow of electric current within the battery itself. When a current \( I \) flows through the battery, the internal resistance causes a voltage drop given by Ohm's Law:
\[
V_{\text{drop}} = I \cdot r_{\text{int}}
\]
### 3. **Effect of Internal Resistance on Terminal Voltage:**
When a battery is under load (i.e., connected to a circuit and delivering current), the terminal voltage \( V_{\text{terminal}} \) is given by:
\[
V_{\text{terminal}} = \text{emf} - V_{\text{drop}}
\]
Substituting the voltage drop due to internal resistance, we get:
\[
V_{\text{terminal}} = \text{emf} - I \cdot r_{\text{int}}
\]
From this equation, it is clear that the terminal voltage is less than the emf when there is a current flowing through the battery. The greater the current, the greater the voltage drop, and hence the lower the terminal voltage.
### 4. **Factors Affecting the Internal Resistance:**
Several factors can affect the internal resistance of a battery:
- **Battery Type and Chemistry:** Different types of batteries (e.g., alkaline, lithium-ion, lead-acid) have different internal resistances due to their varying chemical compositions and designs.
- **Age of the Battery:** Over time, batteries tend to build up internal resistance due to chemical degradation, corrosion, and other factors, leading to a more significant voltage drop.
- **Temperature:** The internal resistance of a battery can change with temperature. Typically, resistance increases at low temperatures, causing a greater voltage drop in cold conditions.
- **State of Charge:** A battery's internal resistance can vary depending on its state of charge. As a battery discharges, its internal resistance may increase, further lowering the terminal voltage.
### 5. **Practical Implications:**
- When using a battery in a device, the voltage you measure across the terminals (the terminal voltage) will usually be lower than the labeled emf. This discrepancy becomes more pronounced under heavy loads (i.e., when the device draws a significant amount of current).
- If a device requires a specific operating voltage, the reduced terminal voltage can lead to malfunction or reduced performance. For example, a flashlight might dim, or an electronic device may not function correctly when the terminal voltage drops too low.
- This also explains why batteries have reduced efficiency at high currents or under heavy loads—more energy is lost internally as heat due to the internal resistance.
### 6. **Example Calculation:**
Consider a 12V battery with an internal resistance of 0.5 ohms. If a device connected to the battery draws a current of 2 amperes, the terminal voltage can be calculated as:
\[
V_{\text{drop}} = I \cdot r_{\text{int}} = 2 \, \text{A} \times 0.5 \, \Omega = 1 \, \text{V}
\]
Therefore, the terminal voltage is:
\[
V_{\text{terminal}} = 12 \, \text{V} - 1 \, \text{V} = 11 \, \text{V}
\]
As shown, the terminal voltage is less than the emf of the battery due to the voltage drop across its internal resistance.
### 7. **Conclusion:**
The terminal voltage of a battery is often less than its emf due to the internal resistance of the battery. When current flows, this internal resistance causes a voltage drop, reducing the terminal voltage. This effect becomes more pronounced with increased current, aging batteries, or under certain environmental conditions, impacting the performance of devices powered by the battery.