Energy

How is energy defined in physics?

Energy is the ability to do work.

What is the SI unit for energy?

The joule (J).

What is kinetic energy?

Kinetic energy is the energy possessed by an object due to its motion.

What is potential energy?

Potential energy is stored energy resulting from an object's position.

What are two common types of potential energy?

Elastic potential energy and gravitational potential energy.

What does the Law of Conservation of Energy state?

Energy cannot be created or destroyed, but it can change from one form to another.

Who discovered the Law of Conservation of Energy in 1842?

Julius Robert Mayer.

What is an energy transfer diagram?

A diagram that shows the useful energy transfers that take place in a process.

How are non-useful energy transfers described?

They are known as waste energy.

What is a Sankey diagram?

A visual representation of energy flow that shows energy stores, transfers, and points of waste.

In a Sankey diagram, what does the width of the arrows represent?

The quantity of energy involved.

In a Sankey diagram, what do the directions of the arrows indicate?

Where the energy flows.

In a Sankey diagram, what does the arrow pointing to the right represent?

Useful energy output.

In a Sankey diagram, what does the downward arrow represent?

Output of wasted energy.

What is the formula for calculating percentage efficiency?

Percentage Efficiency = (Useful Energy Output / Total Energy Input) x 100.

If a device has a total energy input of 100J and a useful output of 10J, what is its efficiency?

10%.

If a device has a total energy input of 100J and a useful output of 75J, what is its efficiency?

75%.

If a device has a total energy input of 2000J and a useful output of 1400J, what is its efficiency?

70%.

Why is energy sometimes described as 'lost' in home energy contexts?

Because energy is transferred into unwanted forms, resulting in inefficiency and higher costs.

What is a BER Certificate?

A Building Energy Rating Certificate that shows how much energy a home uses.

What is the purpose of energy ratings on appliances?

To inform consumers about the energy efficiency of the device.

What term is used to describe energy that has been spread out into the surroundings and is no longer useful?

Dissipated energy.

Does the conservation of energy guarantee that energy is always used in a useful way?

No, energy is always conserved, but it is not always conserved in useful ways.