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Electric Circuits: Understanding Current, Voltage, and Resistance in A-Level Science
What Are Electric Circuits?
Electric circuits are pathways that allow the flow of electric current, driven by a voltage source.
Key Concepts in Electric Circuits
Electric Current (I)
The flow of electric charge through a conductor:
\[ I = \frac{Q}{t} \]
Where:
- \( I \): Current (A)
- \( Q \): Charge (C)
- \( t \): Time (s)
Voltage (V)
Voltage is the potential difference across a component, driving the flow of charge.
Resistance (R)
Resistance opposes the flow of current:
\[ R = \frac{V}{I} \]
Ohm’s Law
Ohm’s Law relates voltage, current, and resistance:
\[ V = IR \]
Series and Parallel Circuits
Series Circuits
- The current is the same through all components
- Total resistance: \( R_{\text{total}} = R_1 + R_2 + \dots \)
Parallel Circuits
- Voltage is the same across all components
- Total resistance: \( \frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \dots \)
Example Problem
A circuit has a \( 12 \, \text{V} \) battery connected to two resistors (\( R_1 = 4 \, \Omega \), \( R_2 = 6 \, \Omega \)) in series. Find the total resistance and current.
- Total Resistance:
\[ R_{\text{total}} = R_1 + R_2 = 4 + 6 = 10 \, \Omega \] - Current:
\[ I = \frac{V}{R_{\text{total}}} = \frac{12}{10} = 1.2 \, \text{A} \]
Applications of Electric Circuits
Electronics
- Powering devices like smartphones and computers
Medical Equipment
- Used in ECG machines to monitor heart activity
Renewable Energy
Common Mistakes in Circuit Calculations
- Mixing up series and parallel formulas for resistance
- Forgetting units (\( \Omega \), V, A)
- Misinterpreting current directions in complex circuits
Practice Questions
- A \( 9 \, \text{V} \) battery powers a \( 3 \, \Omega \) resistor. Calculate the current.
- Explain the differences between series and parallel circuits.
- Describe one application of Ohm’s Law in electronics.
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