Exercises: Generating electrical energy and saving energy

What is a power plant? Explain in your own words what is done there: where does the electricity it produces come from?

In a hydroelectric power plant, there is a reservoir with water stored at a height, as shown in the figure.

Explain where this power plant gets its energy from and what device moves when the water falls.

Look at the wind turbine in the figure:

What moves the blades of a wind turbine? What energy does a wind farm utilize? In what type of locations do you think these wind turbines are installed?

Solar panels on roofs and satellites produce electricity without moving or making noise, like the one in the figure.

What energy do they receive, and what do they transform it into?

Classify these energy sources into renewable and non-renewable: the Sun, wind, coal, water in a reservoir, natural gas, and uranium. Explain the difference between the two groups.

Put these stages of electricity's journey to your house in order: the outlets in your room, the power plant, the cables on high-voltage transmission towers. Explain what happens at each stage.

Why does turning off the light when leaving a room save energy, even if the bulb is small? Explain it by considering the amount of time it stays on.

An LED bulb of $10\ \text{W}$ gives off the same light as an old bulb of $60\ \text{W}$.

1. a) Which one uses less energy to provide the same amount of light?
2. b) How many times more energy does the old bulb use compared to the LED?

In a thermal power plant, the following steps occur, but they are out of order: steam moves a turbine; coal is burned; the generator produces electricity; heat heats water and turns it into steam.

1. a) Put the sequence in order from start to finish.
2. b) What type of energy is stored in coal before it is burned?

A nuclear power plant heats water like a thermal power plant, but without burning anything.

1. a) What "fuel" does a nuclear power plant use?

1. b) State one advantage and one disadvantage of this type of power plant.

State one advantage and one disadvantage of each of these types of power plant: wind and solar. Think about what happens on windless days and at night.

Describe the complete journey of electricity from dammed water in a reservoir to your bedside lamp, naming all the steps: what moves when the water falls, what device generates the current, and how it reaches your home.

A town wants to supply itself with electricity using only solar panels.

1. a) What problem will it face at night and on very cloudy days?
2. b) Propose two solutions to have electricity during those times as well.

In the living room of a house, there are $5$ light bulbs turned on.

1. a) If they are old bulbs, of $60\ \text{W}$ each, what is the total power consumption?
2. b) If they are replaced with LED bulbs of $10\ \text{W}$, which give the same light, what total power do they consume now?
3. c) How much power is saved by making the change?

A TV switched off with the remote control is left with a little red light on: this is standby consumption, or "standby power."

1. a) Do you think it uses energy even though it seems to be off? Justify your answer.

1. b) How would you make it use no energy at all without taking the TV apart?

A cell phone charger plugged into the wall outlet consumes $1\ \text{W}$, even when no phone is connected.

1. a) How many hours does it spend plugged in if it is not unplugged for an entire week?
2. b) How much energy does it consume in that week, in $\text{Wh}$? Hint: multiply power by time.

A valley with a fast-flowing river wants to generate its own electricity and is deciding between a hydroelectric dam and a gas-fired thermal power plant.

1. a) State one advantage of each option.
2. b) State one disadvantage of each option.
3. c) Which would you choose for the valley? Justify your choice using your previous answers.

In nature, we hardly ever find "free" electricity ready to use, except for lightning: it has to be generated by transforming other forms of energy.

1. a) Write down the complete chain of transformations in a thermal power plant, from the energy stored in coal to electricity.
2. b) Using this chain, explain why we say electricity is very convenient to use, but must always be "paid for" with another form of energy.

Nadia's family installs solar panels on their roof, but remains connected to the electricity grid.

1. a) Why do they not completely disconnect from the grid?
2. b) What do you think happens to the excess energy produced around noon on a sunny day?
3. c) What is the advantage of remaining connected to the grid in addition to having solar panels?

The internet router consumes $10\ \text{W}$ and is turned on all day, every day of the year.

1. a) How much energy does it consume in one day, in $\text{Wh}$?
2. b) How much does it consume in a year of $365$ days, in $\text{Wh}$?
3. c) Convert the annual result to $\text{kWh}$, knowing that $1\ \text{kWh} = 1000\ \text{Wh}$.

Emma says: "We should produce all our electricity using renewable energy." Lucas replies: "That's not possible, because the Sun and the wind are sometimes unreliable."

1. a) Explain what each person is right about.
2. b) Name two ways to store or obtain energy for times when the Sun and wind are unavailable.
3. c) Which opinion do you agree with more? Give reasons for your answer.

Household appliances have an energy rating label with a letter, from A (those that consume the least) to G (those that consume the most), like the one in the figure.

1. a) Between two refrigerators of the same size, one rated class A and another rated class F, which would you buy considering the electric bill?
2. b) The class A refrigerator is more expensive to buy; why might it be worthwhile in the long run?
3. c) Why does efficiency matter so much specifically for a refrigerator, which is plugged in $24$ hours a day?

Write an energy-saving plan for your school featuring four measures (think about lights, heating, computers, and blinds).

1. a) Explain why each measure saves energy.
2. b) Which of your measures do you think will save the most energy? Give reasons for your answer.

A region produces its electricity as follows: $40\ \%$ from hydroelectric power plants, $30\ \%$ from wind farms, $20\ \%$ from solar power plants, and $10\ \%$ from a thermal power plant. Look at the graph:

1. a) What percentage of the electricity is renewable?
2. b) If the region produces $2000\ \text{GWh}$ per year, how many $\text{GWh}$ correspond to wind energy?
3. c) How many renewable $\text{GWh}$ does it produce in total?