Simplified P2 - Collecting energy from the Sun, Generating Energy

Question 1

What are the advantages of photocells?

Answer 1

• They are robust and do not need much maintenance
• They need no fuel, and do not need long power cables
• Cause no pollution
• They use a renewable energy source, the sun will continue to burn for another 5 billion years.

Question 2

What are the disadvantages of photocells?

Answer 2

• They do not produce electricity when it is too dark or cloudy
• The current technology is much less efficient than fossil fuels for energy.

Question 3

What does a photocell contain?

Answer 3

A photocell contains two pieces of silicon joined together to make a p-n junction.

Question 4

What is the N type silicon?

Answer 4

It contains an impurity that produces an excess of free electrons.

Question 5

What is the P type silicon?

Answer 5

• It contains an impurity that produces an absence of free electrons.

Question 6

What are photons?

Answer 6

Sunlight contains energy packets, these are photons.

Question 7

What does the output from a photocell depend upon?

Answer 7

The output from a photocell depends upon:

• Light intensity
• Exposed Surface Area
• Distance from light source.

Question 8

What is passive solar heating?

Answer 8

• The sun is very hot and produces infra-red radiation with a very short wavelength
• Glass is transparent to this short wavelength radiation
• The floors and walls inside a building absorb this radiation, warm up and re-radiate infra-red radiation.
• The walls are not as hot as the sun and wavelength radiated is longer
• Glass reflects longer wavelength radiation back inside the building.

Question 9

How are solar reflectors made to be always facing the sun?

Answer 9

Solar reflectors are moved by computers to make sure they are always facing the sun.

Question 10

What type of energy is wind?

Answer 10

Wind is a renewable form of energy.

Question 11

What is an issue with wind energy?

Answer 11

Although it is a renewable form of energy, the wind turbines depend on the speed of the wind.
- Wind turbines will not work if there is no wind, or if the wind speed is far too great.

Question 12

What are some advantages of wind farms?

Answer 12

• They do not contribute to global warming
• An entirely renewable form of energy
• Do not pollute the atmosphere

Question 13

What are some issues with wind farms?

Answer 13

• Less efficient than fossil fuels
• Take up large amounts of space
• Very loud
• People can complain it “ruins the view”.

Question 14

How can you increase the current from a dynamo?

Answer 14

• Using a stronger magnet
• Increasing the number of turns on the coil
• Rotating the magnet faster

Question 15

How can you display the output from a dynamo?

Answer 15

The output of a dynamo can be displayed on an oscilloscope.

Question 16

What does the oscilloscope trace show?

Answer 16

The trace shows how the current produced by the dynamo varies with time.

Question 17

What is the time for one complete cycle called?

Answer 17

The time for one complete cycle is called the period of alternating current.

Question 18

What does a simple generator consist of?

Answer 18

A simple generator consists of a coil of wire rotating between the poles of a magnet:

• The coil cuts through the magnetic field as it spins.
• A current is produced in the coil.

Question 19

How can a current be produced in a simple generator?

Answer 19

• A current can be produced if the coil remains stationary and the magnets move.

Question 20

How are fuels used to heat water at conventional power stations?

Answer 20

• Water boils to produce steam
• Steam at high pressure turns a turbine
• Turbine drives a generator.

Question 21

What is Efficiency?

Answer 21

Efficiency is a measure of how well a device transfers energy.

Question 22

Where is energy lost in a power station?

Answer 22

• Energy in a power station is lost at the boilers, generators, and cooling towers.