Download Radiation - Newark Catholic High School

Chapter 5 & 8
Thermal Energy & Energy Sources
and the Environment
These chapters will have homeworks, a chapter 5 vocabulary quiz, a chapter 8
vocabulary quiz and a combined chapters 5 & 8 test
Chapter 5 Vocabulary
Temperature
Solar Collector
Thermal Energy
Thermodynamics
Heat
First law of thermodynamics
Specific Heat
Second law of thermodynamics
Conduction
Heat Engine
Convection
Internal Combustion Engine
Radiation
Thermal Insulator
Section 1: Temperature, Thermal Energy, and Heat
We can use words like hot and cold to describe temperature. Something is hot when its
temperature is high.
When you heat something its temperature increases.
Temperature and heat have a proportional relationship.
All of the matter around is made of tiny particles. The particles have kinetic energy
because they are moving.
The greater their speeds, the greater their KE.
The more KE the particles of the matter has, the hotter the matter feels.
The temperature [of an object] is the measure of the average kinetic energy of the
particles that make up that object.
In SI units, temperature is measured in kelvins (K).
People around the world use Celsius, and 1 degree C is the same size as 1 K. (we do
not use degrees K, just K)
Thermal Energy (of an object) is the sum of the kinetic energy and the potential energy
of all of the particles that make up that object.
If you let cold butter sit out at room temperature it warms and becomes softer. As the
butter warms and the kinetic energy of the particles increases, the butter's thermal
energy increases.
Thermal energy depends on temperature.
thermal energy of an object increases when the average kinetic energy of the particles
that make up that object increases
So...the thermal energy of an object increases as the temperature increases.
Thermal energy also depends on mass.
if the mass of the object increases, the thermal energy of that object also increases.
The more mass, the more particles, the more energy you have.
Heat is energy that is transferred between objects due to a temperature difference
between those objects.
Warmer objects always heat cooler objects - never the reverse!
EX- a hot stove will heat a cold pot of water.
- Hot air coming in the door in summer (you're not letting the cold air out, but the hot
air in!)
A substance's temperature changes when that substance absorbs thermal energy.
This temperature change depends on the amount of thermal energy that the substance
absorbs and the mass of the substance.
the specific heat [of a material] is the amount of heat needed to raise the temperature
of 1kg of a material by 1oC.
Scientists measure specific heat in joules per kilogram degree Celsius. [J/kg x oC]
Table 1 on page 141 shows the specific heat of common substances.
Water has a high specific heat-it can absorb a lot of thermal energy with little change in
temperature.
Water is a useful coolant because it can absorb so much energy without a change in
temperature.
Thermal energy equation:
Change in thermal energy(J) =
Mass(kg) x Temperature change(oC) x Specific Heat(j/kgoC)
Q = m (T
f-Ti)C
the air in a room has a mass of 50kg and a specific heat of 1000 j/kgoC. What is the
change in thermal energy of the air when it warms from 20oC to 30 oC?
The temperature of a 2.0kg block increases by 5oC when 2000J of thermal energy are
added to the block. What is the specific heat of the block?
HW: Page 143 #4-10
Section 2: Conduction, Convection, and Radiation
Conduction, convection and radiation transfer energy.
Conduction is the transfer of thermal energy by collisions between the particles that make
up matter. (by touching)
Conduction occurs because particles that make up matter are in constant motion.
it transfers thermal energy without transferring matter (a spoon getting hot in a pan of hot
soup)
conduction spreads thermal energy from warmer areas to cooler areas.
The rate at which conduction transfers thermal energy depends on the material.
Conduction is faster in solids and liquids than it is in gases. in gases, particles are farther
apart, so collisions among particles occur less frequently.
The best conductors in thermal energy are metals. This is one reason that pots are made
from metal.
Convection
unlike solids, liquids and gases are fluids that flow. In fluids, convection can transfer
thermal energy.
Convection is the transfer of thermal energy in a fluid by the movements of warmer and
cooler fluid.
when convection occurs, more energetic particles collide with less energetic particles and
transfer thermal energy.
Fluids expand as their temperatures increase, and their density decreases.
The differences in density drive the convection process, creating convection currents.
Convection currents work like a lava lamp:
they contain oil and alcohol- when the oil is
cool, its density is greater so it sits at the
bottom of the lamp. when the light heats the
oil it becomes less dense than the alcohol
and rises to the top, losing heat to the
alcohol as it rises.
this rising and sinking action illustrates a convection current.
Convection currents transfer thermal energy from warmer to cooler parts of the fluid.
Radiation
Radiation is the transfer of energy by electromagnetic waves (light & microwaves)
These waves can travel through space, even when matter is not present!
This is how energy from the Sun gets to Earth!
When radiation strikes a material, that material absorbs, reflects and transmits some of the
energy.
the amount of energy a material absorbs, reflects and transmits depends on the type of
material.
the thermal energy of a material increases when it absorbs radiant energy.
In a solid, liquid, or gas, radiation travels through the space between particles.
Particles can absorb and re-emit the radiation.
Radiation usually passes more easily through gases because the particles are further apart.
Read p148-150 complete 11-14 on p 150
Using Thermal Energy
Heating systemsused in buildings and homes across the world.
First heating system was a campfire, then wood and coal stoves/furnaces
Now:
Forced air systems- the most common type of heating system that is used in the US. A
furnace burns fuel and heats a volume of air, a fan blows warm air through ducts(big
pipes). cool air returns to the furnace through other vents and the furnace reheats it. uses
convection
Radiator systems- closed metal container that contains hot water or steam. a central
furnace heats a tank of water and pipes carry the hot water to radiators in other rooms.
Heat transferred through conduction and convection.
Electric heating systems- electric heating coils transform electrical energy into thermal
energy (portable space heaters). Uses conduction and convection
Solar heating- Energy from the Sun used to heat homes and building two ways:
1. Passive solar heating- materials inside a building absorb radiant energy from the Sun and
heat up during the day. At night the thermal energy absorbed by these materials helps
keep the room warm at night.
2. Active solar heating- uses a solar collector. Solar Collector is a device that transforms
radiant energy from the sun into thermal energy. Radiation from the Sun heats air or water
in a solar collector and a pump circulates the fluid to radiators.
Thermodynamics
Another way to increase the thermal of an object is by using friction and doing work.
Thermodynamics is the study of the relationship between thermal energy, heat, and work.
Heat and work increase thermal energy.
the first law of thermodynamics states that if the mechanical energy of a system is
constant, the increase in thermal energy of that system equals the sum of the thermal
energy transfers into that system and the work done on that system.
This means that there are two ways to increase the temperature of a system.
1. heat the system
2. do work on the system
the second law of thermodynamics states that energy spontaneously spreads from regions
of higher concentrations to regions of lower concentration.
Energy moves from high to low.
Converting Thermal Energy into Mechanical Energy
Done in several ways, steam engines, generators, but mainly through heat engines and
combustion engines.
Heat engine is a device that converts some thermal energy into mechanical energy.
-a car engine (converts chemical energy into thermal energy, then thermal energy into
mechanical energy-used to rotate the cars wheels.)
- only about 25% of the thermal energy released is converted into mechanical energy
Internal combustion engine is a heat engine that burns fuel inside a set of cylinders.
- used in almost all cars now
External combustion engine is a heat engine that burns fuel outside of the cylinders
-old-fashoned steam engine
.