Science chapter 10 Flashcards
The change in temperature indicates
it indicates an increase in our body’s heat production.
Temperature refers to
how hot or cold an object is
Heat energy refers to
the amount of thermal energy that is being transferred from a hotter to a colder region
The SI unit for temperature is
kelvin(K)
The SI unit for heat energy is
joule (J)
When a substance is heated, it undergoes
expansion
When a substance is cooled, it undergoes
contraction
When a substance is heated, it gains heat energy and
expands(increases in volume)
When a substance is cooled, it loses heat energy and
contracts(decreases in volume)
What causes transfer of thermal energy?
difference in temperature
Thermal energy always flows from a region of
higher temperature to a region of lower temperature.
There is no transfer of heat
at thermal equilibrium.
Conduction is the process by which
thermal energy is transmitted from a region of higher temperature to a region of lower temperature from one particle to another through vibrations without any flow in the medium.
Conduction is the only means of transfer of thermal energy in
solid mediums.
How does conduction work?
When one end of a material is heated, particles there gain kinetic energy and vibrate faster and more vigorously.
These particles collide more frequently with less energetic neighbouring particles
causing neighbouring particles to gain kinetic energy.
These neighbouring particles vibrate faster and more vigorously and the energy is passed along to the rest of the particles in the bar.
Why are metals good conductors of heat?
They have free electrons
In non-metals, thermal energy is transferred through the
vibration and collision of particles.
In metals, thermal energy is transferred through
the vibration and collision of particles, and the process of electron diffusion.
In metals, electrons
gain kinetic energy and move more rapidly. They collide with particles in the cooler parts of the metal and pass on their energy in the process.
Conduction of thermal energy in metals is … than in non-metals because conduction takes place through vibrating particles as well as through the free electrons present in metals
far better, conduction takes place through vibrating particles as well as through the free electrons present in metals
Explain the process of free electronic diffusion
When heated, the free electrons gain energy and move faster
These electrons are free to travel in the spaces between the metal particles.
This process is known as free electron diffusion, it is much faster than the conduction by vibration of atoms or molecules that takes place in non-metals.
Hence, metals conduct thermal energy much faster than non-metals which have no free electrons.
In conduction, thermal energy is transferred from one particle to another.
from one particle to another
Convection is the process by which
thermal energy is transmitted from one region to another in a fluid (liquid or gas) by the circulation of currents that direct the movement (flow) of the particles of the fluid.
In convection, thermal energy is transferred
through the actual movement of the heated particles from the warmer to cooler parts of the fluid.
Explain convection in liquid
When the water at the bottom of the flask is heated, it expands.
The expanded water is less dense than the surrounding water and rises.
Since the upper region is cooler, it is denser and therefore sinks.
The difference in the densities of water in the different regions sets up a convection current.
This is shown by purple streams rising from the bottom and sinking at the sides.
Explain convection in gas
When the air above the candle is heated, it expands.
The expanded air is less dense than the surrounding air and rises out of chimney B.
Since the surrounding air is cooler, it is denser and therefore sinks into chimney A.
The difference in the densities of the air at the different chimneys sets up a convection current.
What is radiation
it is the transfer of thermal energy in the form of electromagnetic waves such as infrared radiation without the aid of a medium.
Where can radiation be taken place in?
Radiation can take place in a vacuum. This is how the Earth is warmed by the Sun.
Do All bodies emit infrared radiation?
YAS
Factors that affect the rate of emission and absorption of radiation
Temperature, Surface area to volume ratio, Colour and texture
Objects with a … emit heat at a faster rate.
larger surface area to volume ratio
Rough and black stuff are
better emitters of heat
Poor conductors of thermal energy
air and water
Materials like … are effective insulators because they contain pockets of still air
polyester foam, cork, wool, and fibreglass
Good heat insulators reduce heat by
conduction
Cold air
sinks
Hot air
rises
Shiny and silvery or white surface reduce heat loss or gain by
radiation
white uniform is commonly worn because white surfaces reflect
heat well and are poor absorbers of heat.
How are land and sea breezes formed?
In the day, the land heats up faster than the sea. The air above the land is heated, expands and rises.
Cool air above the sea is denser and moves in to replace the warmer air. This sets up a sea breeze.
At night, the land cools faster than the sea.
The air above the land is now cooler than the air above the sea.
A convection current is set up in the opposite direction. This is called a land breeze.
Black and dull surfaces increase heat loss by
radiation
How does a vacuum flask keep the liquid it contains cool or hot?
Container supported by foam plastic, and covered with a plastic cap, both poor conductors of heat, hence prevent heat loss.
Consists of a double-walled glass container with a vacuum in between – prevent heat loss by conduction and convection.
Silvered walls on vacuum side – reduces heat loss by radiation as heat is release backed into the hot liquid.
