Why does the terminal potential difference of a battery decrease when the current drawn from it is increased?
2 Answers
When you increase the current drawn from a battery, the terminal potential difference (voltage) of the battery decreases due to the internal resistance of the battery. To understand this, let's break it down:
### 1. **Battery Basics:**
A battery consists of two electrodes and an electrolyte that generate electrical energy through chemical reactions. The voltage of the battery, also known as the electromotive force (EMF), is the potential difference between the two electrodes when no current is flowing.
### 2. **Internal Resistance:**
Every real battery has some internal resistance, which is the resistance to the flow of current within the battery itself. This internal resistance is due to factors like the resistance of the electrolyte, the resistance of the electrodes, and any other components inside the battery.
### 3. **Voltage Drop Due to Internal Resistance:**
When a battery is connected to a circuit and current starts flowing, there are two key voltage values to consider:
- **EMF (Electromotive Force):** The maximum potential difference the battery can provide when no current is flowing.
- **Terminal Voltage:** The actual voltage available at the terminals of the battery when a current is flowing.
The terminal voltage (\( V_{terminal} \)) can be calculated using the formula:
\[ V_{terminal} = \text{EMF} - I \cdot R_{internal} \]
where:
- \( I \) is the current flowing through the circuit.
- \( R_{internal} \) is the internal resistance of the battery.
### 4. **Effect of Increased Current:**
When you increase the current drawn from the battery:
- The term \( I \cdot R_{internal} \) increases because the internal resistance \( R_{internal} \) is constant, and \( I \) is increasing.
- This increased voltage drop inside the battery reduces the voltage that appears across the battery terminals.
### 5. **Practical Implications:**
In practical terms, the battery can be thought of as having an "ideal" voltage source (its EMF) and an internal resistor in series. The more current you draw, the greater the voltage drop across this internal resistor, and hence the lower the voltage you measure at the terminals.
For example, if a battery has an EMF of 12V and an internal resistance of 1Ω, and you draw 2A of current, the voltage drop due to internal resistance would be:
\[ \text{Voltage Drop} = I \cdot R_{internal} = 2A \cdot 1Ω = 2V \]
Thus, the terminal voltage would be:
\[ V_{terminal} = \text{EMF} - \text{Voltage Drop} = 12V - 2V = 10V \]
In summary, as the current drawn from a battery increases, the voltage drop across the internal resistance of the battery also increases, leading to a decrease in the terminal potential difference.
### 1. **Battery Basics:**
A battery consists of two electrodes and an electrolyte that generate electrical energy through chemical reactions. The voltage of the battery, also known as the electromotive force (EMF), is the potential difference between the two electrodes when no current is flowing.
### 2. **Internal Resistance:**
Every real battery has some internal resistance, which is the resistance to the flow of current within the battery itself. This internal resistance is due to factors like the resistance of the electrolyte, the resistance of the electrodes, and any other components inside the battery.
### 3. **Voltage Drop Due to Internal Resistance:**
When a battery is connected to a circuit and current starts flowing, there are two key voltage values to consider:
- **EMF (Electromotive Force):** The maximum potential difference the battery can provide when no current is flowing.
- **Terminal Voltage:** The actual voltage available at the terminals of the battery when a current is flowing.
The terminal voltage (\( V_{terminal} \)) can be calculated using the formula:
\[ V_{terminal} = \text{EMF} - I \cdot R_{internal} \]
where:
- \( I \) is the current flowing through the circuit.
- \( R_{internal} \) is the internal resistance of the battery.
### 4. **Effect of Increased Current:**
When you increase the current drawn from the battery:
- The term \( I \cdot R_{internal} \) increases because the internal resistance \( R_{internal} \) is constant, and \( I \) is increasing.
- This increased voltage drop inside the battery reduces the voltage that appears across the battery terminals.
### 5. **Practical Implications:**
In practical terms, the battery can be thought of as having an "ideal" voltage source (its EMF) and an internal resistor in series. The more current you draw, the greater the voltage drop across this internal resistor, and hence the lower the voltage you measure at the terminals.
For example, if a battery has an EMF of 12V and an internal resistance of 1Ω, and you draw 2A of current, the voltage drop due to internal resistance would be:
\[ \text{Voltage Drop} = I \cdot R_{internal} = 2A \cdot 1Ω = 2V \]
Thus, the terminal voltage would be:
\[ V_{terminal} = \text{EMF} - \text{Voltage Drop} = 12V - 2V = 10V \]
In summary, as the current drawn from a battery increases, the voltage drop across the internal resistance of the battery also increases, leading to a decrease in the terminal potential difference.
The terminal potential difference (V) of a battery decreases when the current drawn from it increases due to **internal resistance** within the battery. Here’s a detailed breakdown:
### 1. **Internal Resistance (r)**
Every battery has some internal resistance, denoted as \( r \). This resistance is caused by various factors like the chemical processes inside the battery, the material of the electrodes, and even the construction of the battery. Internal resistance acts like a small resistor inside the battery.
### 2. **Ohm’s Law and Power Distribution**
When a current \( I \) flows through a circuit, including through the internal resistance of the battery, some of the battery’s energy is dissipated as heat within its own internal resistance. The voltage drop across this internal resistance can be calculated using **Ohm’s Law**:
\[
\text{Voltage drop across internal resistance} = I \times r
\]
As the current drawn from the battery increases, this voltage drop across the internal resistance also increases, meaning less voltage is available at the terminals.
### 3. **Terminal Voltage Equation**
The total electromotive force (EMF) or open-circuit voltage of a battery, \( E \), represents the maximum voltage the battery can provide when no current is drawn (i.e., when \( I = 0 \)). However, when a current \( I \) is drawn, the actual terminal voltage \( V \) (the voltage available across the battery’s terminals) is given by:
\[
V = E - I \times r
\]
As the current \( I \) increases, the term \( I \times r \) (voltage drop due to internal resistance) increases, which decreases the terminal voltage \( V \).
### 4. **Practical Example**
- **When the current is low**: \( I \times r \) is small, so the terminal voltage \( V \) is close to the EMF \( E \).
- **When the current is high**: \( I \times r \) becomes large, and the terminal voltage \( V \) drops significantly.
### Conclusion
The decrease in terminal potential difference when more current is drawn from a battery is due to the voltage drop across the internal resistance. The more current you draw, the greater the voltage drop, leading to a lower terminal voltage.
### 1. **Internal Resistance (r)**
Every battery has some internal resistance, denoted as \( r \). This resistance is caused by various factors like the chemical processes inside the battery, the material of the electrodes, and even the construction of the battery. Internal resistance acts like a small resistor inside the battery.
### 2. **Ohm’s Law and Power Distribution**
When a current \( I \) flows through a circuit, including through the internal resistance of the battery, some of the battery’s energy is dissipated as heat within its own internal resistance. The voltage drop across this internal resistance can be calculated using **Ohm’s Law**:
\[
\text{Voltage drop across internal resistance} = I \times r
\]
As the current drawn from the battery increases, this voltage drop across the internal resistance also increases, meaning less voltage is available at the terminals.
### 3. **Terminal Voltage Equation**
The total electromotive force (EMF) or open-circuit voltage of a battery, \( E \), represents the maximum voltage the battery can provide when no current is drawn (i.e., when \( I = 0 \)). However, when a current \( I \) is drawn, the actual terminal voltage \( V \) (the voltage available across the battery’s terminals) is given by:
\[
V = E - I \times r
\]
As the current \( I \) increases, the term \( I \times r \) (voltage drop due to internal resistance) increases, which decreases the terminal voltage \( V \).
### 4. **Practical Example**
- **When the current is low**: \( I \times r \) is small, so the terminal voltage \( V \) is close to the EMF \( E \).
- **When the current is high**: \( I \times r \) becomes large, and the terminal voltage \( V \) drops significantly.
### Conclusion
The decrease in terminal potential difference when more current is drawn from a battery is due to the voltage drop across the internal resistance. The more current you draw, the greater the voltage drop, leading to a lower terminal voltage.