Energy tasks (solutions)

1) A battery is an energy carrier. Because in the battery is energy, with which one can drive a motor.

  • Name three other objects that are also energy carriers and say what you can do with that energy.

2) The wind, i.e. air that moves fast, is also an energy carrier. All objects that move contain kinetic energy.

  • What other forms of energy are there? Give an example of each.
  1. chemical energy: battery, charged battery, coal, gas, oil, wood, bread, potatoes, chocolate, apples.
  2. Heat energy: hot tea, warm air (when exhaling), warm water of a hot water bottle, hot rubbed brake.
  3. electric energy: is transported by the electric current.
  4. Light energy: is in the light of a flashlight or in the light from the sun.
  5. kinetic energy: moving wheel, car, wind, water in a river, running dog.
  6. Tension energy: expander pulled apart, compressed air of an air pump, compressed ball.
  7. Positional energy: man on a five-meter diving tower, water in a reservoir, school bag on a table, airplane up in the sky,

3)" With the energy of one hour of sunlight on a square meter, you can charge a car battery."

  • Form three more sentences in this way.
  1. With an inflated bicycle tire one can lift a school satchel six times on a one meter high table. (Or lifting six satchels on a one meter high table or lifting one satchel on a 6m high table.)
  2. With the energy of two bars of chocolate you can charge a car battery or ca. to boil 7 liters of water.
  3. With the energy of a cyclist you can boil 1/100 l, that is 10ml of water.
  4. With the energy of one liter of boiling water you can push 10 bicyclists up to 30 km/h.

Energy converter / energy reloader

1) A car engine gets its energy from the gasoline and sets the car in motion. The engine also gets very hot. The engine recharges the energy from the gasoline to the movement of the car and to the hot engine.

2) Energy for man, a cow and for plants:

For a person who eats only meat, there is at least one more transloader, the animal being eaten. A cow is a pure herbivore, if you eat predators like tuna, or omnivores like the pig, you add more energy reloaders. This is also the reason why a vegetarian diet has less impact on the ecosystem. (Planet Knowledge)

Curious people ask now where the sun gets its energy from. It gets it from the hydrogen atoms, which "fuse" in the sun to helium atoms, this is called nuclear fusion. But where do the hydrogen atoms get their energy from?? These have got the energy probably already with the birth of the universe, with the big bang. Where the energy for the big bang came from, nobody knows exactly, in addition one can read perhaps in the Bible the Genesis.

3) This table of energy reloaders is filled in completely.

4) Energy chains

The energy reloading chains are mixed up! Cut out the individual parts and put them in the right order.

a) A "Flummi is picked up from the ground and released. It falls, bounces up again, it falls and bounces up again, etc.

In the beginning, humans use the chemical energy of food to lift the flummi, giving it positional energy. As it falls, the ball gets faster and faster: the positional energy gets smaller and the kinetic energy increases.
When the bouncer hits the ground, it is compressed and slowed down: The kinetic energy decreases and is stored as tension energy in the bouncer.
After that the flummi relaxes again, pushes itself away from the ground and "jumps" high: The tension energy becomes again movement energy.
The flummi "flies then upwards and becomes slower and slower: the kinetic energy becomes positional energy again. Now the game can start again.
Because with each bounce the ball heats up a little bit, each time some energy goes into the flummi as heat energy, so it bounces a little less high.

b) A ball of dough is lifted up and dropped down. It falls to the ground and stays there. After that, the ball has a dent on the bottom side.

When the dough hits the ground, it deforms and becomes warm. So the kinetic energy of the dough is used to heat the dough.

c) You draw the bow and release the string. The arrow flies away and gets stuck in the target.

When the dart hits the target, friction generates heat. The kinetic energy of the arrow goes into the heated target and the heated arrowhead.

d) The "grasshopper is pressed onto the table, the suction cup holds it in place. A short time later it jumps up, falls down again and stays on the table.

Energy losses and efficiency

1) "A car engine has an efficiency of approx. [math]1/3 \approx 33 \%[/math] ."

2) This energy flow diagram shows the path of energy in a coal-fired power plant.

3) If many energy converters are connected to form a chain, the total efficiency is calculated by multiplying all the individual efficiencies.(Table of efficiencies)
If a person rides a bicycle having eaten a loaf of bread before, the energy is to be given off with the movement:

[math] 35\% \cdot 30\% = 035 \cdot 03 = 0105 =105 \%[/math]

The total efficiency is approx. 10%. This means ca. 10% of the energy from the sunlight has arrived in the movement.

a) Calculate the total efficiency of:

1. a light bulb that is powered by a coal-fired power plant. The power plant has an efficiency of 35%, the light bulb of only 4%: [math]35\% \cdot 4\% = 035 \cdot 004 = 0014 = 14\%[/math] So only 1.4% of the coal energy comes out with the light from the bulb again! 2. the energy transfer chain of the steam engine: steam engine> Generator> Incandescent lamp. The steam engine has an efficiency of 5%, the generator 85% and the light bulb 4%: [math]5\% \cdot 85\% \cdot 4\%= 005 \cdot 085 \cdot 004 = 00017 = 017\%[/math] Only 0.17% comes out of the energy of the gas with the light of the lamp again!

b) Compare the efficiency of:

1. a gasoline car with an electric car charging the battery with a coal power plant. The power plant has an efficiency of 35% and the electric motor of the e-car of 95%: [math]35\% \cdot 95\% = 035 \cdot 095 = 03325 \approx 33\%[/math] The gasoline powered car has a comparable efficiency of 35%. (However in the city traffic substantially less!)
So, an electric car makes sense mainly if the battery is charged with renewable energies. 2. a gas heater with an electric heater powered by a coal-fired power plant. The coal-fired power plant has an efficiency of 35% and the electric heating has an efficiency of 100%: [math]35\% \cdot 100\% = 035 \cdot 1 = 035 = 35\%[/math] So the electric heating uses only 35% of the coal energy. In comparison, a gas heating uses 85% of the energy used!

Energy in the household

1) Saving energy in the household

In a household one needs energy for the many electrical devices, like washing machine, lamps, computer. and for the heating, the warm water and for the car.

    one finds a diagram showing what an average household uses a lot of energy for and what it uses less for: half for heating the home, a third for driving, and the rest for hot water and electrical appliances in equal parts.

2) Calculate energy amounts and costs

Peter’s desk lamp has an output of 20 watts. He turns them on the day ca. 2 hours on. For one kilowatt hour of energy, his electricity provider charges 25 cents.

  • How much energy is needed to turn on the lamp for one second, one minute or one hour?

The lamp requires 20J of energy every second:

  • How much does the desk lamp cost Peter per month and per year??

One watt-hour of energy is equal to 3600 joules of energy. A device with one watt of power needs exactly one watt-hour of energy in one hour, because one hour has 3600 seconds. One kilowatt-hour is one thousand watt-hours:

Peter needs 1.2kWh energy per month and 14.4kWh energy per year for the lamp. That costs him 30Cent in the month and 3,60Euro in the year.

3) Different light sources

Herbert doesn’t like the light of energy-saving lamps and therefore illuminates his living room with an incandescent lamp. Andrea, on the other hand, has bought energy-saving lamps for the entire apartment, while Maria has opted for LED lamps.

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