Chapter 10: Heat Flashcards
Define ‘temperature’
It is a measure of how hot an object is
What is the SI unit for temperature?
Kelvin (K)
What happens when 2 objects are in contact? (Heat transfer)
Heat energy is transferred from the hotter object to the colder object. This causes the temperature of the hotter object to decrease and the temperature of the colder object to increase until both objects reach the same temperature/ equilibrim.
What happens to a substance upon heating?
It will gain heat and expand, causing its volume to increase while its density decreases.
What happens to water upon heating from the heat source below a pot of water?
The water at the bottom will gain heat and expand, causing its volume to increase and its density to decrease. This causes the water to rise to the top, thus forming a convection current
What happens when water at 0-4°C is heated? (Short ans)
It will gain heat and contract. (vice versa)
What happens to a solid upon cooling?
The solid will lose heat and contract, causing the volume to decrease and its density to increase.
Which state of matter does expansion occur the most and least in?
Most: Gas
Least: Solid
What happens when a liquid is cooled?
It will lose heat and contract, causing its volume to decrease and its density to increase, thus cool water sinks, which creates a convection.
What state of matter does contraction occur the most and the least in?
Most: Gas
Least: Solid
What are some examples of real-life applications to counter effects of expansion and contraction?
- Gaps between railway tracks
- Sagging telephone lines
- Rollers on bridge
What are bimetallic strips used in?
Thermostats.
What does a thermostat do?
It helps to keep the temperature of an appliance constant.
What is a bimetallic strip?
It is made out of two different metals welded together where one expands and contracts more than the other upon the same change in temperature.
If the brass is on the bottom of bimetallic strip, what happens when it is heated up?
Brass will expand more and become longer, causing the bimetallic strip to bend upwards.
If brass was on the bottom of the bimetallic strip and it expands and contracts more than the other metal, what would happen when it is cooled?
Brass will contract more and it will become shorter, causing the bimetallic strip to bend downwards.
What is conduction?
It is the transfer of heat energy without the physical movement of the medium.
How is heat transferred via conduction?
The heat source will heat up the object. The hotter end of the object has a high vibration of atoms, meaning that the particles will become faster as there is more heat energy. Particles in the object collide with each other and pass on the heat energy to the next particles until the object reaches an equilibrim
Why does conduction take place the best in solids?
The particles are the closest to each other and can transfer the heat energy from one particle to another particle the quickest.
Why can’t conduction occur in vacuum?
There are no particles at all.
Why does conduction occur the best in metals?
There are free moving electrons to help transfer the heat energy from one end of the material to the other end.
What is the factor that affects the rate of conduction?
Different materials
What is convection?
It is the transfer of heat energy from one place to another by the physical movement of a medium.
What states of matter can convection take place in?
Liquid and gas.
What causes a convection current to be set up?
Because of the changes in density
What are the conditions needed for a convection current to be set up effectively?
Heat source must be at the bottom OR cooling source must be at the top
What is radiation?
The transfer of energy from a hotter body to a cooler body without the need for a medium.
What are the 3 factors that affect rate of radiation?
- Temperature of object
- Surface area of object
- Type of surface (Texture and colour)
What is the relationship between radiation and the temperature of an object?
The hotter the body of an object, the higher the rate of radiation from the object.
Why do objects with a larger surface area have a higher rate of radiation?
The large surface area allows heat to be radiated away quickly.
What are the characteristics of black/ dark and dull and rough surfaces?
They are better emitters and absorbers of radiation.
What are the characteristics of white/ light and smooth and shiny surfaces?
They are poor emitters and absorbers of radiation.
