Light = Electromagnetic Radiation · the heat of the metal will quickly go into the water. after 5 minutes: the water with plastic will be warmer. Because plastic has a higher specific

Light = Electromagnetic Radiation

What is light? Kurzgesagt

What is light? Dave

Thermal Radiation: Heat is lost through Thermal Radiation (IR) by all objects, all the time.

Hotter objects emit more radiation.

Thermal Radiation is a type of “light” AKA: electromagnetic radiation.

Just like all waves, EM waves require a medium. However, the medium they use is not made of matter.

EM waves are disturbances in the electric and magnetic fields that exist in all locations. Even outer space where there is no matter.

Depending on the electron configuration of the atoms, EM waves can be

Reflected orAbsorbed orTransmitted

Light transmission, absorption, reflection Bozeman

Electromagnetic waves (thermal radiation) are emitted when charged particles accelerate. Hotter objects have more frequent atom collisions and the collisions are harder/faster, so the have more charged particles accelerating, which means more EM radiation waves.

Would making this bottle out of glass slow heat loss?

Would making this bottle out of glass slow heat loss?

Slower conduction out the top

How would glass coated with silver help?

Radian Energy would be reflected back in.

How would glass coated with silver help?

Should the glass be coated on the outside surface or the inside surface?

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The inside surface would make the better thermos.

Glass

Vacuum

CCR Heat transfer Eureka

CCR Heat transfer study.com

CCR Heat transfer Bozeman

IR camera experiments.

Thermal Energy:The sum of the kinetic energy of the particles of an object.

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The thermal energy of an object will depend on the number of particles and the Kinetic Energy (mass and speed) of the particles.

The temperature of the object is a measurement of the average KE of the particles.

Higher temperature means faster moving particles.

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HEAT: is a term used to describe Thermal Energy when it is transferred from one object to another.

HEAT = Thermal Energy = Q

When an object cools it gives off heat.IOW

When an object cools thermal energy leaves the object and goes into another object.

Some materials are harder to heat up than others.

It takes 1 Calorie (kilocalorie) to heat up a kg of water 1 C

It takes 1/10 of a Calorie to heat up a kg of copper 1 C

It takes 1/2 of a Calorie to heat up a kg of plastic 1 C

1 Calorie kg of water 1 C

1/10 of a Calorie kg of coper 1 C

1/2 of a Calorie kg of plastic 1 C

Why is this a better slide? to scale

It takes more energy to heat up water than any

other common material.

Specific Heat:The amount of heat needed to raise the

temperature of 1 g of a material by 1 °C

Specific to different types of materials.

If the specific heat = 3

Then it will take 3 J of energy to raise 1 g 1

Specific Heat:Directly related to the amount of heat held by

each gram of material.

If the specific heat = 2

Then every gram has 2 J of energy to give up for

each 1 of temperature it looses.

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Which would stay hot longer?

specific heat 1.0 specific heat 4.0

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Which would stay hot longer?

specific heat 1.0 specific heat 4.0

300 g100 g

In order for the rocks to go down 1 degree each gram must give off 1.0 J of energy.

So if 300 grams goes down 1 degree the rocks must loose 300 J.

Which would stay hot longer?

specific heat 1.0 specific heat 4.0

300 g100 g

In order for the waterto go down 1 degree each gram must give off 4.0 J of energy.

So if 300 grams goes down 1 degree the rocks must loose 300 J.

So if 100 grams goes down 1 degree the water must loose 400 J.

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Assuming the two buckets are conducting and radiating at the same rate. It will take longer to loose 400 J than to loose 300 J so the water will stay warm longer.

So if 300 grams goes down 1 degree the rocks must loose 300 J.

So if 100 grams goes down 1 degree the water must loose 400 J.

Heat of vaporization: energy needed to change 1 gram of liquid into a gas.

Water has an extremely high Heat of Vaporization.about 2000 joules per gram.

It takes 4 J to raise the temperature of a gram of water from 98 - 99 C

It takes 2000 J to raise the temperature of a gram of water from 99-100 C

For every gram of water that evaporates 2000 J of heat are taken from the body.

Heat of fusion: energy needed to change 1 gram of solid into a liquid.

Water has a Heat of Fusion of about 300 joules per gram.

So each gram of ice must absorb 300 joules of Heat in order to melt, before it can increaseits temperature.

In this experiment heat is added at a constant rate to the water. As time goes by the temperature is measured.The results are used to plot a graph of temp. vs time.

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Temperature of the ice is increasing as heat is added. (2 J /gram/degree)

Temperature remains the same as heat is

added. All the energy is being used to cause a

phase change.

Temperature of the liquid is increasing as heat is added. The slope is less

steep because it takes more energy for each degree of temperature change.

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Temperature remains constant as the heat is used to cause a phase

change (vaporization)It remains constant for a longer

duration due to the high amount of “heat of vaporization”.

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Expect a handful of questions aboutthis graph on the test.

𝑸 = 𝒎 ∗ 𝚫𝑻 ∗ 𝒄Q = change in thermal energy (heat) Measured in J

m = mass Measured in g

c = specific heat

ΔT = change in temperature

Measured in J/g/degree °C

Measured in °C

specific heat = how hard it is to make change temperature.IOW: how much energy is needed to change temp.also: how much energy is given off when a gram goes down 1 C

A wooden block has a mass of 20 g and a specific

heat of 1.7 J/(g oC). Find the change in thermal

energy of the block as it warms from 15 oC to 25 oC.

m = 20 g

c = 1.7 J/(kg oC)

Ti = 15 oC

Tf = 25 oC

Q = ?

Q = mcΔT

Q = mc(Tf – Ti)

Q = (20)(1.7)(25-15)

Q = (20)(1.7)(10)

Q = 340 J

The air in a living room has a mass of 6 g and a specific heat of 1.02 J/g oC. What is the change in thermal energy of the air when it warms from 20 oC to 25 oC?

Answer: Q = 30.6 J

𝑸 = 𝒎𝚫𝑻𝒄

𝑸 = 𝟔 ∗ 𝟓 ∗ 𝟏. 𝟎𝟐

The thermal energy of water in a mug increases by

12,600 J when the water is heated from 20 oC to 40 oC.

If the specific heat of water is 4.18 J/g oC, what is the mass of the water?

Answer: m = 150 g

𝑸 = 𝒎𝚫𝑻𝒄

𝟏𝟐, 𝟔𝟎𝟎 = 𝒎 ∗ 𝟐𝟎 ∗ 𝟒. 𝟏𝟖

Why does a handle of metal pan feel hotter than an handle of plastic pan? (when taken from an oven)

FYI: things feel hot when they heat up your skin. You don't actually feel the object, you feel your skin's reaction to the object.

When you grab a handle heat will move into your skin by conduction. In the metal pan you will draw heat from molecules far from the surface, since the Thermal Energy travels quickly through the conductive material.

In the plastic handle you will only draw heat from molecules on the surface, since the Thermal Energy travels slowly through the insulating material.

On a hard surface more atoms are in contact so more heat can transfer. On carpet there are fewer atoms actually in contact with skin.

Would a tongue stick to a cement pole?No, because cement is less conductive so the tongue would not loose

as much heat into the object (only the surface atoms will absorb the heat), The tongue would NOT get cold enough to freeze.

tongue looses 20 Cspit freezes

tongue looses 6 C spit does not freeze

Which hot handle would heat up the cup of water the most? It depends on when you check it. after 5 seconds: the water with

metal will be warmer.Because it is a good conductor so allthe heat of the metal will quickly go into the water.

after 5 minutes: the water with plastic will be warmer.Because plastic has a higher specific heat it will release more total Heat.It takes more time because the plastic is not a good conductor, so the heat from the inner atoms takes a while to reach the surface and leave the handle.

RS page 21Thermal Energy

Worksheet