Energy efficiency
Energy Efficiency
Law of Conservation of Energy
Definition: The law of conservation of energy states that energy cannot be created or destroyed; it can only be transformed from one form to another or transferred between systems.
Explanation of Total Energy Maintenance: In a closed system, total energy remains constant through energy transfers and transformations.
Energy transformations occur but the total amount of energy is conserved.
Example: A light bulb converts electrical energy into light and heat; however, the total energy before and after the transformation is the same.
Concept of Efficiency
Efficiency: Efficiency measures how much of the input energy is transformed into useful output energy.
Formula for Efficiency:
Expressed as a percentage, a higher percentage indicates greater efficiency.
Energy Systems
Types of Energy Systems
There are three types of energy systems that describe how energy and matter are exchanged or conserved.
Open Systems
Closed Systems
Isolated Systems
Open Systems
Definition: An open system is one that exchanges both energy and matter with its surroundings.
Characteristics:
Matter can flow in and out.
Energy (in the form of heat or sound) can flow in and out.
Example: A boiling pot without a lid.
Process: Steam (water molecules - matter) escapes, and heat (energy) is transferred.
In an open system, although total energy changes, the combined energy of the system and surroundings is conserved.
Closed Systems
Definition: A closed system exchanges energy but not matter.
Characteristics:
Matter remains fixed within the system’s boundaries.
Energy can enter or leave.
Example: A sealed pressure cooker.
Process: No mass escapes, but heat energy flows in.
The total amount of energy remains constant; changes occur only due to energy crossing the boundary.
If the system gains energy, the surroundings lose the same amount.
Isolated Systems
Definition: An isolated system does not exchange energy or matter with its surroundings.
Characteristics:
No transfer of matter or energy occurs.
Example: An ideal thermos (perfectly insulated and sealed).
These are theoretical approximations, yet they serve as useful models in physics.
Key Principle: Total energy remains constant as nothing enters or leaves the system. Changes must be internal transformations (e.g., kinetic energy transforming into thermal energy).
Investigation on Energy Systems
Investigation 1.2 - Open and Closed Systems
Half-fill two large conical flasks with water that is near boiling.
Caution: Handle hot flasks carefully!
Quickly record the temperature of the water in each flask with a thermometer.
Remove the thermometer and seal one of the flasks.
Record the mass of each flask and its contents using electronic scales.
After 1–2 days, record the mass of each flask and its contents again.
Remove the stopper from the sealed flask and record the temperature of the water again.
Useful vs Wasted Energy
Energy Transfers: When energy is transferred in a system, not all of it is utilized effectively.
Useful Energy: The energy that performs the intended function.
Example: Light energy from a lamp, which helps us see effectively.
Wasted Energy: Energy that is not useful for the intended purpose and is often lost to surroundings.
Example: Heat energy released from a lamp.
Conservation Principle: Energy is never truly lost; wasted energy is simply transformed into less useful forms (often heat or sound).
Table 1.1 - Energy Transformations in Common Electrical Appliances
Device | Original Form of Energy | Transformed to Useful Energy | Transformed to Wasted Energy |
|---|---|---|---|
Microwave Oven | Electrical Energy | Heat (thermal) energy of food | |
Gas Cooktop | Chemical Energy | Heating air and food | Heating air, producing light and sound |
Car Engine | Chemical Energy | Kinetic energy of the car | Heating moving parts due to friction, heating circuitry and surrounding air |
Desktop Computer | Electrical Energy | Light and sound energy |
Questions
Question Set 1: A motor takes in 200 J of energy and produces 120 J of useful movement energy.
a) Calculate the efficiency of the motor.
b) How much energy is wasted?Question Set 2: A light bulb uses 80 J of electrical energy each second but only converts 16 J into useful light energy.
a) Calculate its efficiency.
b) Identify the main form of wasted energy.Question Set 3: Kevin calculates the efficiency of a fan in his room.
Total energy input: 1000 J.
Energy transformation: Kinetic energy (700 J), Sound energy (200 J), Thermal energy (100 J).
Useful energy output is the kinetic energy (700 J).
Sankey Diagrams
Purpose of Sankey Diagrams: Diagrams can illustrate the transfers and transformations of energy within a system.
Example: Energy transformations that occur in an LED light bulb can be summarized visually using a Sankey diagram or a simple energy flow diagram.
Example Calculation of Kinetic Energy Transfer: When you rub hands together, kinetic energy transforms into heat energy and some sound energy.
Diagrammatic Representation: Simple and Sankey diagrams can be illustrated for this transformation.
Activities for Energy Efficiency
Activity CS - Energy Efficiency: Assess energy efficiency through various exercises.
Activity PS - Energy Efficiency Worksheet: Engage with practical applications of energy efficiency concepts through provided worksheets.