Collecting energy from the Sun

Question 1

Advantages of photocells

Answer 1

• They are robust and do not need much maintemance.
• They need no fuel or long power cables.
• They cause no pollution and do not contribute to global warming.
• They use a renewable energy source.

Question 2

Disadvantage of a photocell

Answer 2

They do not produce electricity when it is dark or too cloudy.

Question 3

What are the main components of a photocell?

Answer 3

Two pieces of silicone (p-type and n-type) joined together to make the p-n junction.

Question 4

Why does the n-type and p-type silicon have different have different charges?

Answer 4

• The n-type silicone has an impurity that gives it an excess amount of free electrons.
• The p-type silicone has a different impurity that gives it an absence of free elctrons.

Question 5

What do photons do in a photocell?

Answer 5

Photons from the sun cause free electrons to move producing an electric current.

Question 6

What factors affect the output of a photocell?

Answer 6

• Light intensity.
• Surface area exposed.
• Distance from the light source.

Question 7

What is the process of passive solar heating?

Answer 7

1. The sun is very hot and produces infrared radiation with a short wavelength.
2. Glass is transparent to this short wavelength radiation.
3. The walls and floor inside a building absorb this radiation, warm up and re-radiate infrared radiation.
4. The walls and floor are not as hot as the Sun so the wavelength radiated is therefore longer.
5. Glass reflects this longer wavelength radiation back inside the building.

Question 8

How does the hemisphere a house is located in affect the direction that a window needs to be in for passive solar heating?

Answer 8

• In the southern hemisphere, large windows in a house need to face north towards the sun.
• In the northern hemisphere they face south.

Question 9

How are are solar reflectors made more efficient?

Answer 9

With computers that make sure they are always facing the direction of the sun.

Question 10

Wind is a renewable form of energy but …

Answer 10

It does not depend on the speed of the wind.

Question 11

When will the wind turbines not work?

Answer 11

• If there is no wind.
• Or if the speed of the wind is too great.

Question 12

Advantage and disadvantages of wind farms

Answer 12

• They don’t contribute to global warming or pollute the atmosphere.
• They can be noisey
• They take up alot of space.
• People complain they ruin the view.