practice

What is the law of conservation of energy?

• Energy cannot be created or destroyed, but can be transformed from one type to another

• Energy can be transformed from one type to another

• Energy can be created but not destroyed

• Energy is constant in the universe

What is a watt a unit of?

• Speed

• Force

• Power

• Energy

How did Lord Kelvin and Hermann von Helmholtz propose the Sun might produce energy?

• By the mechanical motion of meteorites falling into it

• By converting chemical energy into heat

• By burning coal and wood

• By converting gravitational energy into heat

What happens when the outer layer of the Sun falls inward according to Kelvin and Helmholtz's hypothesis?

• The Sun stops shining

• The Sun expands in size

• The atoms acquire additional speed and temperature increases

• The Sun cools down

How long could the Sun shine at its present rate if it were to contract at a rate of 40 meters per year?

• 10 billion years

• 1 billion years

• 100 million years

• 10 million years

What did scientists discover in the twentieth century about the true source of the Sun's energy?

• It is powered by nuclear fusion

• It is powered by solar panels

• It is powered by chemical reactions

• It is powered by gravitational contraction

What is the primary source of energy for stars that are just being born?

• Nuclear fusion

• Solar panels

• Gravitational contraction

• Chemical reactions

What did Charles Darwin worry about in relation to the age of the solar system?

• The Sun's age

• The Sun's size

• The Sun's brightness

• The Sun's energy source

What did geologists and physicists show about the age of the Earth and the Sun in the late nineteenth and early twentieth centuries?

• They are much younger than previously thought

• Their age cannot be determined

• They are the same age as previously thought

• They are much older than previously thought

What two key pieces of information were required to solve the puzzle of the Sun's energy source?

• The structure of the nucleus of the atom and the fact that mass can be converted into energy

• The discovery of a new type of energy and the age of the Sun

• The discovery of a new planet and the brightness of the Sun

• The temperature of the Sun and the distance from Earth