8.3 Conduction, convection, radiation, and evaporation Flashcards
define conduction
form of heat transfer in which thermal energy passes through a substance from particle to particle. Conduction mainly occurs in solids.
define insulator
a material which is a poor thermal conductor
define convection
form of thermal transfer in which thermal energy causes a substance to expand and rise. This then cools and sinks. Convection only occurs in gases and liquids.
define convection current
the movement of particles in fluid due to convection
define fluid
a substance that can flow from one place to another - a gas or liquid
define radiation
form or energy transfer in which thermal energy is released as infrared radiation. There is no change in matter for energy to transfer in this way.
define absorb
take in energy
define emit
give out energy in the form of radiation
define evaporation
when a liquid turns into a gas, at a temperature lower than the boiling point. An evaporating liquid takes energy with it and so it cools the surface it was evaporating on.
Why are frying pans made out of metal
Metals are good conductors of heat. So, they can heat up and cook the food a lot faster than other materials.
Why are pan handles made of plastic or wood and not from metal
Plastic and wood are insulators. As they do not conduct heat very well, the person using the pan will not get burned when touching the handle of the pan
To keep warm, you are told to wear several layers of clothes. This traps air between the layers. Why is this good at keeping you warm?
Multiple layers trap warm air in between the layers, acting like an insulator. So, it helps you keep warm.
Why are solids the best conductors?
Why are gases the worst conductors?
Since the particles in solids are closer, it is fast at transferring energy between the particles.
As gases have a lot of space between each particle, the energy takes longer to transfer between particles.
When liquids and gases are heated, their particles start moving around faster. What does this do to the distance between the particles?
The distance between the particles is decreased as they bump into each other a lot more often.
When a fluid is heated, what happens to the density of the liquid or gas?
They are less dense. Because the particles move around more and spread out.
Why does convection happen in liquids and gases, but not in solids?
Because for convection to take place, the molecules in the substance should be free to move. In solids the particles are packed together, so there isn’t space for the particles to move.
Why can’t convection happen in a vacuum
There are no particles in a vacuum, so convection cannot happen
Why can you feel the warmth from a fire if you are standing sideways to it?
The thermal radiation of the fire spreads out in all directions, so you will be able to feel the warmth from sideways.
Why does the heat from the Sun not reach us by conduction or convection?
There is vacuum in between the Earth and the Sun, so conduction and convection cannot take place.
What are the ways that a vacuum flask keeps hot liquids hot, and cold liquids cold?
Plastic cap (Insulator)
Silvered surfaces (silvered surfaces are good reflectors of heat)
Vacuum between the glass walls
Difference between evaporating an boiling?
Evaporation is slow, occurs at all temperatures, and does not produce bubbles.
Boiling is quick, occurs at a fixed temperature, and bubbles are formed throughout the liquid.
