P2 - Living for the Future

Question 1

Explain how a photocell generates electricity from sunlight.

Answer 1

• A solar cell, made out of two silicon (P and N type), generates direct current:
  1. The silicon absorbs energy from the sunlight.
  2. Electrons are knocked free from the silicon atoms.
  3. Electrons flow freely, forming a current.

Question 2

How can large curved mirrors be used to produce electricity?

Answer 2

1. A large curve mirror focuses (via reflection) sunlight onto a single point.
2. As a result, energy is concentrated on this point; heating it up.
3. This can be used to heat up water, producing steam which can then be used to operate an electricity-generating turbine.

Question 3

Explain passive solar heating.

Answer 3

1. Light from the sun has a short wavelength, so can pass through glass windows into home.
2. Objects in the house then absorb this energy from the sun.
3. The heated objects in the room emit longer wavelength IR radiation, which cannot exist through the glass windows. As a result, it is reflected back.
4. This results in a greenhouse effect which keeps the home warm.

Question 4

How can a solar collector be made most efficient?

Answer 4

It must track the position of the Sun so that it is always directly facing it.

Question 5

How do solar water heaters use passive solar heating?

Answer 5

1. Glass lets heat and light from the sun in, which is absorbed by black pipes.
2. Water is heated up inside the pipes.
3. Hot water pumped around the house.

Question 6

What is electromagnetic induction?

Answer 6

The creation of a voltage in a wire which is experience a change in magnetic field.

Question 7

What is the dynamo effect?

Answer 7

An electrical conductor moves through a magnetic field, or a magnetic field moves past an electrical conductor, to generate electricity.

Question 8

How do generators move a coil to create electricity?

Answer 8

1. Generators rotate a coil inside a magnetic field.
2. Every half a turn, the current in the coil swaps direction.
3. As a result, generators produce alternating current (AC).

Question 9

How is electricity generated in a power station?

Answer 9

1. Fuel is burnt to heat water.
2. Steam produced
3. Steam spins turbine.
4. Turbine rotates generator.

Question 10

Explain the greenhouse effect.

Answer 10

• Shorter wavelength EM radiation from the sun is absorbed by and heats up the Earth.
• The Earth re-radiates this energy as longer wavelength infrared radiation.
• Greenhouse gases absorb some of the infrared radiation, warming up the atmosphere.

Question 11

Explain how and why transformers are used in the national grid.

Answer 11

1. AC begins with large current, low voltage.
2. Step-up transformers increase the voltage, therefore reducing the current. As current is reduced, electrical cables on pylons are heated less, so less energy is wasted/lost.
3. At neighbourhoods, step-down transformers decrease the voltage, therefore increasing the current. It is unsafe for homes to have high-voltage electricity, but homes need large currents for appliances.

Question 12

What is the penetrating power of alpha, beta and gamma radiation?

Answer 12

Alpha - stopped by a few sheets of paper.
Beta - stopped by a few mm of aluminium.
Gamma - (mostly) stopped by few CM of lead

Question 13

Why can nuclear radiation have negative impacts on human health?

Answer 13

Nuclear radiation can ionise cells in the human body. This can lead to mutations, and cause unwanted chemical reactions.

Question 14

What is plutonium?

Answer 14

• A waste product from nuclear reactors.

- Used to make nuclear bombs.

Question 15

How can we dispose radioactive waste?

Answer 15

• Encased in glass and stored underground.
• Reprocessed.
• Low-level waste in landfill sites.

Question 16

List problems associated with dealing with radioactive waste:

Answer 16

• Remains radioactive for long period of time.
• Terrorist risk.
• It may come into contact with groundwater.

Question 17

Why do objects, such as planets, follow an orbital motion in our solar system?

Answer 17

The centripetal force of gravity is acting on them.

Question 18

List difficulties faced by manned spacecraft:

Answer 18

• The need to carry lots of food, water and oxygen.
• The need to regulate the temperature and remove toxic gasses.
• Astronauts need to be shielded from harmful radiation.
• Muscle wastage and loss of bone tissue as a result of low gravity.
• Psychologically stressful for astronauts.

Question 19

Explain the advantages and disadvantages of using unmanned spacecraft to explore:

Answer 19

Advantages:

• No need for food, water or oxygen.
• Can withstand lethal conditions.
• They’re much cheaper.
• No astronauts taking up room.
• No loss of life on mission failure.

Disadvantages:

• Can’t think for themselves, unable to solve complex problems that might arise.
• An unmanned spacecraft can’t maintain or repair itself.

Question 20

Describe the make-up of a comet.

Answer 20

• Made from ice and dust.

- Tail formed from a trail of debris

Question 21

What is a meteor?

Answer 21

A rock that has entered the Earth’s atmosphere.

Question 22

Describe how a collision between two planets can

result in an Earth-Moon system:

Answer 22

1. Two planets collide.
2. Their iron cores merge.
3. The remaining less dense material orbits the Earth as the moon.

Question 23

What evidence is there for the theory that the moon came from a collision between the Earth and another planet?

Answer 23

• The moon has a lower density than the Earth, and doesn’t have a big iron core like the Earth does.
• Moon rocks contain few substances which evaporate at low temperatures - suggesting that the Moon formed from hot material (the type of conditions that would result from a collision).

Question 24

Why does the speed of a comet increase as it approaches a star?

Answer 24

• The force of gravitational attraction increases as the comet approaches a large mass such as a star.
• As a result, the comet speeds up

Question 25

Explain why the asteroid belt is between Mars and

Jupiter.

Answer 25

Because Jupiter is such a large planet, it causes a huge amount of gravitational pull.

This huge gravitational attraction interfered with the rocks between Mars and Jupiter - preventing a planet from forming.

Question 26

Why are NEOs difficult to spot?

Answer 26

They’re often small, dark and have unusual orbits.

Question 27

Why is red-shift evidence for the big bang?

Answer 27

• The more distant a galaxy is from the Earth, the more it appears to be on the red-end of the spectrum.
• This is because their light is being received at a lower frequency, since it is travelling away from us.
• This means that the universe is expanding.

Question 28

Describe the life history of a star.

Answer 28

1. Interstellar gas cloud.
2. Gravity makes gas and dust spiral into each other to form a protostar. The gravitational energy is then converted into heat energy.
3. When the temperature gets high enough, the hydrogen nuclei undergo nuclear fusion to form helium nuclei; mass amounts of heat and light released.
4. The heat being released balances out with the inward force of gravity, making the star stable (this is when it’s a main sequence star).
5. Eventually, hydrogen runs out and star swells into red giant.

Question 29

Describe the end cycle of a small star.

Answer 29

1. Main sequence star becomes red giant.
2. Becomes unstable, ejects outer layer of dust and gas as planetary nebula.
3. This leaves behind a solid core, a white dwarf, that eventually fades away.

Question 30

Describe the end cycle of a large star.

Answer 30

1. Min sequence star becomes red supergiant as a result of undergoing more fusion and creating heavier elements.
2. Eventually, the star explodes in a supernova.
3. A very dense core, a neutron star, is left behind. If the star is beg enough, a black hole is created.

Question 31

Describe the properties of a blackhole.

Answer 31

• So dense that nothing (even light) can escape its strong gravitational pull.
• Black holes have very large mass, small volume, and very high density.
• They’re not visible.

Question 32

What evidence did Galileo find for the Copernican model?

Answer 32

Using a telescope, he saw some stars that were in a line near a planet. When he looked again, the stars didn’t seem seem to move and carried along with the planet - this suggested they weren’t stars, but moons orbiting Jupiter.

This proved that not everything orbited the Earth.

Question 33

How did scientific advancements allow the Copernican theory to develop?

Answer 33

Today, we still think that planets in our system orbit the sun. However, today, we know that the planets don’t orbit the sun in perfect circles - but rather, in elliptical orbits.

Question 34

Explain how cosmic background radiation is evidence for the big bang theory.

Answer 34

• Low frequency microwave radiation coming from all directions and all parts of the universe.
• When the universe expands and cools, the background radiation cools and drops in frequency.
• This is evidence for the big bang.