1.7 Energy, work and Power

Question 2

What is power?

Answer 2

Power is the work done per unit time or the energy transferred per unit time.

Question 3

What is the unit of power?

Answer 3

The unit of power is the Watt (W).

Question 4

What is the formula for power?

Answer 4

Power (P) = Work Done (W) / Time (t)
or
Power (P) = Energy Transferred (E) / Time (t)

Question 5

What are some energy resources obtained from chemical energy?

Answer 5

Chemical energy can be obtained from:

Fossil fuels (coal, oil, natural gas)

Biofuels (e.g., wood, ethanol, biodiesel)

Question 6

What are renewable energy sources related to water?

Answer 6

Water-based renewable energy sources include:

Energy in waves

Tidal energy

Hydroelectric power from dams

Question 7

What is geothermal energy?

Answer 7

Geothermal energy is the energy obtained from the Earth’s internal heat, used for heating or generating electricity.

Question 8

What is nuclear energy?

Answer 8

Nuclear energy is non-renewable and comes from the energy stored in atomic nuclei, often used in nuclear power plants to generate electricity.

Question 9

How does solar energy work?

Answer 9

Solar energy can be harnessed through:

Solar cells (to generate electrical power)

Solar panels (to heat water using infrared and other electromagnetic waves from the sun)

Question 10

What is wind energy?

Answer 10

Wind energy is the energy derived from the movement of air, often captured by wind turbines to generate electricity.

Question 11

What is the main source of energy for most energy resources?

Answer 11

Radiation from the sun is the main source of energy for all our energy resources.

Question 12

Which energy resources do not rely on radiation from the sun?

Answer 12

Geothermal

Nuclear

Tidal

Question 13

How is energy released in the Sun?

Answer 13

Energy is released by nuclear fusion in the Sun.

Question 14

What is being researched regarding nuclear fusion?

Answer 14

Research is being done to investigate how energy released by nuclear fusion can be used to produce electric energy on a large scale.

Question 15

What are Sankey diagrams used for?

Answer 15

Sankey diagrams are used to represent energy transfers. They show the energy input, useful energy output, and energy lost (such as wasted energy). The width of the arrows in the diagram represents the amount of energy.

Question 16

What is the ratio of useful energy or power output to total energy or power input called?

Answer 16

The ratio is called Efficiency.

Question 17

What is the formula for efficiency?

Answer 17

Efficiency = (Useful Energy Output / Total Energy Input) × 100%

Question 18

What is kinetic energy?

Answer 18

Kinetic energy is the energy an object has due to its mass and speed.

Question 19

What is the formula for kinetic energy?

Answer 19

The formula for kinetic energy is:
K = ½mv²

Where:

KE is kinetic energy (in joules, J)

m is mass (in kilograms, kg)

v is speed (in meters per second, m/s)

Question 20

What is gravitational potential energy?

Answer 20

Gravitational potential energy is the energy an object has due to its height in a gravitational field.

Question 21

What is the formula for gravitational potential energy?

Answer 21

The formula for gravitational potential energy is:

GPE=mgh

Where:

GPE is gravitational potential energy (in joules, J)

m is mass (in kilograms, kg)

g is gravitational field strength (approximately 9.8 m/s² near Earth’s surface)

h is height (in meters, m)

Question 22

What is the formula for change in gravitational potential energy?

Answer 22

The formula for change in gravitational potential energy is:

ΔGPE=m⋅g⋅Δh

Where:

ΔGPE is the change in gravitational potential energy (in joules, J)

m is mass (in kilograms, kg)

g is gravitational field strength (approximately 9.8 m/s² near Earth’s surface)

Δh is the change in height (in meters, m)

Question 23

What are the different forms in which energy can be stored?

Answer 23

Kinetic

Gravitational potential

Chemical

Elastic (strain)

Nuclear

Electrostatic

Internal (thermal)

Question 24

How is energy transferred?

Answer 24

Energy is transferred between stores during events and processes, such as when an object moves, heats up, or changes shape.

Question 25

What is energy transfer by forces (mechanical work)?

Answer 25

Energy is transferred by forces—also known as mechanical work—when a force acts on an object. Examples include pulling, pushing, and stretching.

Question 26

What is energy transfer by electrical currents (electric work)?

Answer 26

Energy is transferred by electrical currents when an electric charge (current) moves through a potential difference.

Question 27

What is energy transfer by heating?

Answer 27

Energy is transferred by heating when it moves from a hotter object to a colder one.

Question 28

What is energy transfer by waves?

Answer 28

Energy can be transferred by electromagnetic waves (like light, infrared, or radio waves) and sound waves. For example, light transfers energy from the Sun to the Earth.

Question 29

What is the principle of conservation of energy?

Answer 29

The principle of conservation of energy states that energy cannot be created or destroyed. It can only be transferred from one store to another or transformed from one type to another.