Nuclear Fission And Fusion

Question 0

What fuel is usually split in the process of nuclear fission?

Answer 0

Usually uranium 235 though sometimes plutonium 239 or both

Question 1

What is nuclear fission?

Answer 1

The splitting up of big atomic nuclei

Question 2

How do nuclear power stations work?

Answer 2

In a nuclear reactor, a controlled chain reaction takes place in which atomic nuclei split up and release energy in the form of heat. This heat is used to heat water to make steam which drives the steam turbine which is connected to an electricity generator.

Question 3

Advantages of nuclear fission:

Answer 3

Nuclear fuel is cheap
Can continuously provide electricity
Provides lots of energy

Question 4

Disadvantages of nuclear fission:

Answer 4

Power plant is expensive
Decommissioning and dismantling is expensive
Waste disposal is difficult
Risk of radiation leaks

Question 5

What is nuclear fusion?

Answer 5

The joining of small atomic nuclei

Question 6

What releases more energy, fission or fusion?

Answer 6

Fusion

Question 7

Advantages of nuclear fusion

Answer 7

Environmentally friendly
Doesn’t leave loads of radioactive waste
Plenty of hydrogen to use for fuel

Question 8

Disadvantages of nuclear fusion

Answer 8

Fusion can only occur at very high temperatures-about 10,000,000 degrees
You can’t hold the hydrogen at the high temperatures and pressures required for fusion in an ordinary container, you need a very strong magnetic field.

Question 9

How do protostars form?

Answer 9

From clouds of dust and gas, the force of gravity makes the dust and gas spiral in together and form a protostar.

Question 10

When making a protostar, what causes the dust and gas to spiral in together?

Answer 10

Gravity

Question 11

Why does the temperature of a protostar rise?

Answer 11

The gravitational energy is converted into heat

Question 12

What happens when the temperature of a protostar gets high enough?

Answer 12

Hydrogen nuclei undergo nuclear fusion to form helium nuclei and give out masses of heat and light.

Question 13

What is the long stable period that is found in a main sequence star?

Answer 13

Where the heat created by nuclear fusion provides an outward pressure to balance the force of gravity pulling everything inwards.

Question 14

Why can a star maintain its energy output for millions of years?

Answer 14

Due to the masses of hydrogen it consumes.

Question 15

What happens when the hydrogen begins to run out?

Answer 15

Heavier elements such as iron are made by nuclear fusion of helium. The star then swells into a red giant if it’s a small star or a red super giant if it’s a big star.

Question 16

Why do red giants and super red giants turn red?

Answer 16

Because the surface cools.

Question 17

What happens to a small to medium sized star like the sun after the red giant stage?

Answer 17

It becomes unstable and ejects its outer layer of dust and gas as a planetary nebula.

Question 18

What does a planetary nebula leave behind?

Answer 18

A hot dense solid core- a white dwarf, which just cools down to a black dwarf that eventually disappears.

Question 19

What happens to big stars after the red super giant stage?

Answer 19

They start to glow brightly again as they undergo more fusion. They expand and contract several times, forming elements as heavy as iron in various nuclear reactions. Eventually they explode in a supernova forming elements heavier than iron and ejecting them into the universe to form new planets and stars.

Question 20

What happens after the exploding supernova?

Answer 20

The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a neutron star. If the star is big enough this will become a black hole.

Question 21

Name the stages in a life cycle of a star:

Answer 21

Dust and gas.
Protostar.
Main sequence star
Red super giant. Red giant.
Supernova. (Planetary nebula)
Neutron star. White dwarf.
Black hole.

Question 22

Why is fusion not used to generate electricity at present?

Answer 22

Fusion only works at such high temperatures that it uses more energy than it could produce.