Forms of Energy and Transformations

State what form of energy each of these things has:

1. a) A kite flying high at the beach.
2. b) Water stored in a reservoir, at the top of the dam.
3. c) A new, unused battery.
4. d) The flame of a camping stove.

Match each form of energy to its example and write out the four complete pairs:

1. a) Nuclear energy.
2. b) Wind energy.
3. c) Sound energy.
4. d) Electrical energy.

Examples: the doorbell, a windmill, the wall socket and the Sun.

The wind turns the colourful pinwheel that Nico has planted in the garden, as shown in the figure.

1. a) What form of energy does the moving air have?
2. b) What form of energy do the pinwheel blades have as they rotate?

Vera has left her book on the top shelf of the bookcase, as shown in the figure.

1. a) What form of energy does the book have because it is so high up?
2. b) If the book falls, into what form of energy is that energy transformed while it falls?

In a thermal power plant, natural gas is burned to generate electricity. The diagram of the plant is as follows:

The chain of transformations is out of order:

1. a) Electrical energy.
2. b) Chemical energy of the gas.
3. c) Kinetic energy of the turbine.
4. d) Thermal energy of the water vapour.

Write it in order using arrows, from the gas to the power grid.

An electric car is charged at a house with solar panels, as shown in the figure.

1. a) Write the complete chain of transformations, from sunlight to the motion of the car. It must include at least four forms of energy.
2. b) State two moments in that chain where some energy is lost as heat.
3. c) Some electric cars recharge the battery slightly when braking. What energy transformation do they take advantage of to do this?

In an old light bulb, out of every $100\ \text{J}$ of electrical energy, only $10\ \text{J}$ are converted into light. The figure shows this energy flow.

1. a) How many joules are lost as heat?
2. b) Why does it burn to touch one of these light bulbs after it has been on for a while?

An old light bulb transforms $100\ \text{J}$ of electrical energy into $10\ \text{J}$ of light. An LED bulb transforms the same $100\ \text{J}$ into $40\ \text{J}$ of light. The figure compares the energy flow of the two bulbs.

1. a) How much energy does each one lose as heat?
2. b) Which one would you choose for your home? Justify your answer using the data.
3. c) In summer it is hot at home. Explain why having many old light bulbs switched on can make the air conditioning use even more energy.

Complete the sentence with the missing words: "Energy is neither created nor destroyed, it is only $\dots$ from one form to $\dots$". Then give an everyday example in which this happens.

Aitana swings on a swing higher and higher. The figure shows the swing at the highest point (A) and at the lowest point (B).

1. a) What form of energy does she have at the highest point, where she stops for a moment?
2. b) And what form of energy does she have when passing through the lowest point?
3. c) If nobody pushes her, she goes less high each time. What "thief" takes away part of the energy and into what form does it convert it?

On a roller coaster, the carriage is stopped at the top of a $30\ \text{m}$ hill and then drops almost to the ground, as shown in the figure.

1. a) Describe the energy transformation that takes place on the way down.
2. b) If there were no friction at all, to what height could it climb on the next hill? Why?
3. c) In reality it always climbs a little less. Into what has the "missing" energy been converted?

An electric heater of $2\ \text{kW}$ is switched on for $3\ \text{h}$. How much energy does it consume? Express it in $\text{kWh}$.

A washing machine of $2\ \text{kW}$ does a wash cycle that lasts $1.5\ \text{h}$.

1. a) How much energy does it consume, in $\text{kWh}$?
2. b) If a kilowatt-hour costs $4\ \text{\$/kWh}$, how much does that wash cycle cost?

The microwave oven at home consumed $7.2\times10^{6}\ \text{J}$ in one month. Knowing that $1\ \text{kWh} = 3.6\times10^{6}\ \text{J}$:

1. a) How many $\text{kWh}$ has it consumed?
2. b) How much did that month of microwave use cost, at $4\ \text{\$/kWh}$?