Conservation and Dissipation of Energy

This section explains conservation and dissipation of energy covering, energy transfers in the system, energy efficiency and the energy efficiency formula, power and the formula for power and thermal insulation. 

Energy Transfers in a System

Energy can be transferred between different stores but is always conserved—it cannot be created or destroyed, only transferred. The main ways energy can be transferred are:

• Mechanically – by a force doing work (e.g. pushing an object).
• Electrically – by an electric current (e.g. a kettle heating water).
• By heating – energy transferred due to a temperature difference.
• By radiation – energy transferred by waves (e.g. light, sound).

When energy is transferred, some is often dissipated (spread out and lost as heat, sound, or light), making the process less efficient.

Energy Efficiency

Efficiency is a measure of how much useful energy is transferred compared to the total energy supplied.

Formula for Efficiency

$$\text{Efficiency} = \frac{\text{Useful energy output}}{\text{Total energy input}} \times 100$$ 

Efficiency is often given as a percentage.

Example Calculation

A motor receives 200 J of electrical energy and produces 120 J of useful kinetic energy. Calculate its efficiency.

$$\text{Efficiency} = \frac{120}{200} \times 100$$

$$\text{Efficiency} = 60\%$$

So, the motor is 60% efficient.

Power

Power is the rate at which energy is transferred or the rate at which work is done.

Formula for Power

$$P = \frac{E}{t}$$

Where:

• $P$ = power (Watts, W)
• $E$ = energy transferred (Joules, J)
• $t$ = time (seconds, s)

Example Calculation

A hairdryer transfers 2,400 J of energy in 30 seconds. Calculate its power.

$$P = \frac{2400}{30}$$

$P = 80 W$

So, the hairdryer has a power output of 80 W.

Thermal Insulation

Thermal insulation reduces energy loss by slowing down the transfer of heat. This is important in homes to improve energy efficiency and reduce heating costs.

Ways to Reduce Energy Loss in Homes

Loft insulation – Reduces heat loss through the roof by using insulating materials like fibreglass.

Double glazing – Reduces heat transfer through windows by trapping air between two glass panes.

Cavity wall insulation – Reduces conduction and convection by filling wall gaps with insulating foam.

Carpets and curtains – Reduce heat loss through floors and windows.

Draught excluders – Prevents warm air from escaping through doors and windows.

By using good thermal insulation, homes become more energy efficient, reducing wasted energy and lowering heating costs.

This guide covers key concepts in conservation and dissipation of energy, including energy transfers, efficiency, power, and insulation. Understanding these principles helps in solving real-world energy problems.