Energy, Power and Resistance This topic explores the fundamental concepts of electrical energy , power , and resistance , essential for understanding electrical...
This topic explores the fundamental concepts of electrical energy, power, and resistance, essential for understanding electrical circuits in A Level Physics AS. We will delve into Ohm's law, the factors affecting resistance, and the calculations of electrical energy and power.
Ohm's law states that the current I flowing through a conductor between two points is directly proportional to the voltage V across the two points, provided the temperature remains constant. This relationship can be expressed mathematically as:
V = I × R
where R is the resistance in ohms (Ω).
The resistance of a conductor depends on several factors:
Resistivity is a property of the material that quantifies how strongly it resists electric current. It is defined as:
ρ = R × (A/L)
where ρ is the resistivity, R is resistance, A is the cross-sectional area, and L is the length of the conductor.
The electrical power P consumed by a circuit can be calculated using the formula:
P = V × I
Additionally, using Ohm's law, power can also be expressed as:
P = I² × R or P = V² / R
Efficiency is a measure of how much input energy is converted into useful output energy. It can be calculated using:
Efficiency (%) = (Useful power output / Total power input) × 100
Understanding energy, power, and resistance is crucial for analyzing electrical circuits. Mastery of these concepts allows students to apply their knowledge in practical situations and prepares them for further studies in physics.
Problem: A resistor with a resistance of 10 Ω has a current of 2 A flowing through it. Calculate the voltage across the resistor and the power dissipated.
Solution: