Energy
What is the law of conservation of energy?
The law of conservation of energy states that energy can neither be created nor destroyed - only converted from one form of energy to another.
Define heat
Thermal energy that is transferred from one object to another
Name 3 examples of poor conductors
Wood, Rubber, Plastic, Glass
Convection involves air or liquids where ___ ___ rises and ___ ___ sinks
Hot air/water rises and cold water/air sinks
What is radiation?
Radiation heat transfer is a process where heat waves are emitted.
What is it meant by "Energy Efficiency"?
Energy efficiency simply means using less energy to perform the same task – that is, eliminating energy waste.
Identify whether the following statement is true or false.
Heat naturally moves from a cooler object to a warmer object.
FALSE
It moves from hot to cold
At the beach, rubber sandals will prevent your feet from burning on the hot sand.
Determine whether rubber is an insulator or conductor or neither
Insulator
Poor conductor = insulator
Define convection by completing the sentence.
Convection is heat transfer:
A. where one substance passes all of its energy to another substance
B. between objects that are touching
C. within fluids between areas of different temperature
D. through empty space
C
A pizza is cooking in a wood-fired oven.
Select which of the following is the best example of radiation.
A. The bricks transfers heat to the pizza dough
B. The coals transfer heat to the oven and pizza
C. Hot air cooks the toppings on the pizza
B
The particle model theory is...
The kinetic theory of matter (particle theory) says that all matter consists of many, very small particles which are constantly moving or in a continual state of motion. The degree to which the particles move is determined by the amount of energy they have and their relationship to other particles.
Identify whether the following statement is true or false AND WHY
If the particles in a substance have a lot of kinetic energy then the substance has a lot of thermal energy.
TRUE
A substance with a lot of thermal energy has particles that move a lot. Therefore, the particles have a lot of kinetic energy.
Conduction is...and where does it occur more readily in?
Conduction is the process by which heat energy is transmitted through collisions between neighboring atoms or molecules. Conduction occurs more readily in solids and liquids, where the particles are closer together than in gases, where particles are further apart.
At a school camp, Antonio is worried that it will be too hot in the cabin to sleep. Which bunk bed – top or bottom – would give him the best chance of staying cool? Explain your choice.
Antonio should sleep in a bottom bunk to help stay cool.
Hot air in the cabin is less dense than the cooler air, and will therefore rise. Cooler air is more dense and will remain in the lower part of the cabin.
Why does heat only travel by radiation to Earth?
Because there are not enough particles in space to transfer heat by moving around or passing on vibrations.
Name two energy transformations which result in energy being wasted as either heat, sound or both.
Your phone wastes energy as heat as it gets hotter the more you use it
A light bulb generates heat as well as light, A TV generates heat as well as sound and light
When water is cooled it loses thermal energy. It may freeze to form solid ice. Identify and describe what happens to the kinetic energy of its particles.
It decreases
The kinetic energy of the particles decreases as a substance loses thermal energy. This means that the particles are moving less. In liquid water, the particles move around each other. In solid ice, the particles vibrate in fixed positions.
Saucepans are usually made of metal but often have plastic or wooden handles.
Explain why these materials are a good choice in relation to the conduction of heat.
Metals are good conductors of heat, so this allows the saucepan to transfer heat to the food inside. Using a conductor for the body of the saucepan helps to cook the food more efficiently.
Plastic and wood are good insulators that transfer heat much more slowly. They are therefore less likely to heat up while cooking, making them easier and safer to use. If the handle is also made of metal then heat quickly travels through it and reaches your hand. This could make it too hot to hold and put you at risk of burns.
When fluids are heated or cooled, their density changes. Describe the changes in fluids that are heated and cooled in relation to their density and particle movement/energy
When fluids are heated, their particles move more quickly and gain kinetic energy. As the particles move about more, they spread further apart. The fluid expands and becomes less dense.
When fluids are cooled, their particles move more slowly and lose kinetic energy. As the particles move less, they are closer together. The fluid contracts and becomes denser.
Jasmine is deciding whether to wear a white T-shirt or a black T-shirt on a very hot day.
Which one should she choose? Explain your reasoning, in relation to radiation.
Jasmine should choose the white T-shirt to help her stay cooler. This is because the white T-shirt will reflect radiant heat.
If she chose the black T-shirt she would feel hotter because it would absorb more infrared radiation and heat up.
A particular electric car is supplied with 300 kJ of chemical energy by the battery. Of this, a total of 70.5 kJ of energy is wasted as heat.
Calculate the overall efficiency of the electric car.
Chemical energy in the battery = 300 kJ
Waste heat energy = 70.5 kJ
Useful kinetic energy$$=300 − 70.5
$$=229.5kJ
$$efficiency = useful output energytotal input energy × 100%
$$=229.5300×100%
$$=76.5%
The overall efficiency of the electric car is 76.5%.
A drop of red food dye is added to a beaker with hot water. Blue food dye is added to a beaker with cold water.
Explain the difference in the way that the dye moves in each beaker using the terms particles and kinetic energy.
The particles in the hot water move more and have more kinetic energy than the particles in the cold water. Therefore, when the food dye is added to the hot water the dye spreads quickly.
The particles in the cold water move less and have less kinetic energy than the particles in the hot water. When food dye is added to the cold water, it spreads more slowly.
Describe why do metal objects in a room usually feel colder than wooden objects feel colder than wooden objects when you touch them, even though they are both at the same temperature?
(for example, a metal door handle feels colder than the surface of a wooden table)
Metals are much better conductors of heat than wood. The metal door handle will therefor conduct away from your fingers, making your fingers feel colder.
The wood, however, is not as good a conductor of heat and therefore will not conduct heat away from your fingers as well as metal. The wooden table therefore does not feel as cold to the touch.
When you swim in a calm lake, the top layer of water can be noticeably warmer because it's been heated by the Sun.
Explain why it's difficult for the warm upper layer to mix with the cooler water underneath.
Sunlight heats the top layer of water, increasing its thermal energy. This makes it expand and become less dense than the colder water underneath.
This is a stable situation because the less dense, warmer water will remain floating on top of the denser, colder water. Convection will not occur because there is no reason for the warmer water to flow downwards and mix with the cooler water.
State and describe the 3 ways how radiant heat can strike a surface (including their temperature changes i.e if it increases or decreases etc)
Transmission - Clear objects (glass) allow light and radiant heat to pass through. Temperature does not increase quickly when heat reaches through by radiation.
Absorption - Dark coloured absorb light and radiant heat. Temperature increases quickly when heat reaches through.
Reflection - Shiny or light coloured surfaces reflect light and radiant heat away. Temperature does not change quickly when heat reaches them.