Energy stores and transfer
Energy efficiency
Temperature and thermal energy
Heat transfer
Examples
100
Name four types of energy transfer.
Electrical, mechanichal, heating, raduation.
100
The law of energy conservation tells about two main things to know about energy. Name them.
Energy can not be created or destroyed.
100
Name three states of matter and the processes of changing from one state to another (four of them).
Solid - melting - liquid - boiling (evaporating) - gas.
Gas - condensation - liquid - freezing - solid.
100
This is the heat transfer between two objects that touch each other.
Conduction.
100
Name energy transfer type that happens when you walk barefoot on a hot sand.
Conduction.
200
Name at least 6 types of energy stores (of total 8).
Thermal, kinetic, potential gravitationel, potential elastic, chemical, electrostatic, magnetic, nuclear.
200
In a light bulb only 10% of total energy is transferred as light. What is happening with the rest 90%?
The rest 90% is transfered as heat into the thermal store of surroundings.
200
The temperature of an object is related to...?
How fast the particles of the object move.
200
A type of heat transfer that does not need any matter to travel through.
Radiation.
200
Explain what is happening. What type of heat transfer do we observe?
Air is heated with the candle and it flows upwards making the spiral rotate. This is an example of convection.
300
Name all energy stores used in a working battery powered fan.
Chemical (battery), kinetic (rotating fan, motor), thermal (motor, wires).
300
Give the name of a diagram that is used to show energy transfer. What does the arrows' thikness show?
Sankey diagram. Arrow thickness shows the amount of energy being transferred.
300
The thermal energy of an object is related to...?
How fast the particles of the object move AND how many particles are there in the object.
300
This is the transfer of heat by physical upward movement of particles. What state of matter is needed for it to happen?
Convection. It happens in fluids (liquids or gases).
300
Watch the demonstration with a baloon. Explain what is happening. What type of heat transfer did we observe?
First demo: a baloon is heated and the rubber melts, that is why it pops.
Second demo: water in a baloon absorbs the heat transfereed from rubber, so the rubber temperature does not increase and it does not melt.
This is an example of conduction.
400
Describe why energy can be called "the money of phyiscs"? Give at least 3 points of similarity.
Like the money, energy can be:
1. Stored in different stores.
2. Transferred between them.
3. But it will be the same total amount.
4. And it will be the same money (currency).
400
Give a definition of energy efficiency.
Energy efficiency is a measure of how much useful energy is transferred.
400
Explain why the temperature of solid matter is always less than the temperature of the same matter in liquid state.
The particles of matter will move slower (only vibrate) in a solid than in a liquid.
400
Describe how the three types of heat transfer occur in Earth's atmosphere heating.
•Energy is transferred from the Sun as radiation.
•Earth’s surface absorbs this energy and transfers it with conduction into the air.
•Energy is transferred from lower warm air to upper cold air with convection.
400
Watch the demonstration with a pencil lead. Explain what is happening. What types of energy stores and transfers were used?
Chemical store (battery) - electrical transfer - thermal store (pencil lead) - heating and light radiation - surroundings.
500
Name energy stores and transfers in a working hydropower plant: it uses falling water to rotate turbine, that turns electrical generator, that gives away electricity we can use for our appliances.
Potential gravitational store (water upstream) - mechanical transfer (falling water) - kinetic store (turning the turbine) - mechanical transfer (from turbine to generator) - kinetic store (rotating generator) - electrical transfer (generator transfers electricity to the network).
500
Draw a diagram and calculate the efficiency of electrical motor (in %) if it loses 300 j of 1000 j total energy input as heat and sound.
Input 1000 j = 100%, energy loss 300 j = 30%, useful energy 1000-300=700 j = 70%.
500
Describe why more time is needed in the same microwave to heat larger glass of milk to the same temperature as the smaller one?
The larger glass contains more milk, that means we need to make more particles move faster. It takes more energy and so it takes more time (in the same microwave oven).
500
Why does jumping into a cold water make you feel cold? What transfer is occurring?
The heat is flowing out of the body into the cold water through conduction.
500
Give examples of four main types of energy transfer.
Some examples:
Electricity going from the power plant to the lamp in the room.
Spinning the bicycle pedals.
Drying out wet clothes on the heater.
Multimedia projector projecting the presentation on the screen.