Chapter 14: Problem 40
The voltage \(V\) in a simple electrical circuit is slowly decreasing as the battery wears out. The resistance \(R\) is slowly increasing as the resistor heats up. Use Ohm's Law, \(V=I R,\) to find how the current \(I\) is changing at the moment when \(R=400 \Omega\) \(I=0.08 \mathrm{A}, d V / d t=-0.01 \mathrm{V} / \mathrm{s},\) and \(d R / d t=0.03 \Omega / \mathrm{s}\)
Short Answer
Step by step solution
Differentiate Ohm's Law
Substitute Known Values
Simplify the Equation
Solve for \(\frac{dI}{dt}\)
Calculate \(\frac{dI}{dt}\)
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Ohm's Law
- Voltage (\( V \)): the potential difference across the circuit component.
- Current (\( I \)): the flow of electric charge through the circuit.
- Resistance (\( R \)): the opposition to the flow of current, measured in ohms (\(\Omega\)).
Time Derivatives
- \(\frac{dV}{dt}\): Represents the rate of change of voltage with respect to time, indicating how quickly the voltage is decreasing or increasing.
- \(\frac{dI}{dt}\): Represents the rate of change of current with respect to time, which our problem asks us to find.
- \(\frac{dR}{dt}\): Represents the rate of change of resistance, indicating how the resistance is changing as the circuit operates.
Rate of Change
To find \( \frac{dI}{dt} \), we differentiate Ohm's Law with respect to time, resulting in an equation that includes all relevant rates of change. This equation was:\[ \frac{dV}{dt} = \frac{dI}{dt} \cdot R + I \cdot \frac{dR}{dt} \]This formula shows that:
- The rate at which voltage changes is influenced by how quickly the current and resistance are changing.
- By finding \( \frac{dI}{dt} \), we can determine how the current is adjusting because of the changes in voltage and resistance.
Electrical Circuits
In the problem, we considered a circuit where both the voltage supplied by a battery and the resistance of a resistor were changing over time. These changes influenced the electric current flowing through the circuit.
- A battery provides the voltage, a necessary push that moves electrons through the circuit.
- A resistor opposes this flow, creating a restriction that affects the overall current.