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Resistors: Understanding Resistance and Its Role in A-Level Science
What Is a Resistor?
A resistor is a component that restricts the flow of electrical current in a circuit.
Resistance and Its Formula
Resistance (RRR)
Resistance is defined by Ohm’s Law:
R=VIR = \frac{V}{I}R=IV
Where:
- RRR: Resistance (Ω\OmegaΩ, Ohms).
- VVV: Voltage (VVV, Volts).
- III: Current (AAA, Amperes).
Types of Resistors
Fixed Resistors
Provide a constant resistance value.
Variable Resistors (Potentiometers)
Allow adjustment of resistance in a circuit.
Applications of Resistors
Current Limitation
Used to control the amount of current flowing through a circuit.
Voltage Division
Divide voltage across components in a circuit.
Heating Devices
Resistors convert electrical energy into heat in devices like toasters and heaters.
Example Problem
A 9 V9 \, \text{V}9V battery powers a circuit with a 3 Ω3 \, \Omega3Ω resistor. Find the current.
- Formula:
I=VRI = \frac{V}{R}I=RV
- Substitute Values:
I=93=3 AI = \frac{9}{3} = 3 \, \text{A}I=39=3A
Common Mistakes in Resistor Calculations
- Mixing up voltage and current in Ohm’s Law.
- Forgetting to account for total resistance in series and parallel circuits.
- Ignoring power dissipation in resistors.
Practice Questions
- A 12 V12 \, \text{V}12V battery powers a circuit with R=6 ΩR = 6 \, \OmegaR=6Ω. Calculate the current.
- Explain the role of resistors in protecting LEDs.
- Describe how variable resistors are used in volume controls.