a partial physics breakdown

8/20/2019 A Partial Physics Breakdown

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PART 1

1.What is temperature?

Temperature is the degree or intensity of heat present in a substance orobject, especially as expressed according to a comparative scale and

shown by a thermometer or perceived by touch.

2. Identify Physical properties which vary with temperature and

which therefore maybe used as the basis for measurin temperature.

• !enth- as a substance is heated the length will increase for

example. a copper rod• "olume- as temperature is increased the volume increases for

example. gases, metals

• Resistance- as temperature increases particles in a solid move more

vigorously and restrict the flow of electrons.

• Pressure- as temperature increases pressure increases because there

is more collisions between the particles and container, increasing

the force within the same area.

#. $efine fi%ed points on the &elsius scale 'upper and lower fi%ed

points(

A fixed point is a melting or boiling point of a pure substance

therefore it will always have the same value on a scale foe example.

The upper and lower fixed point of the Celsius scale.

• The upper fixed point is the boiling point of pure water 1!!

degrees Celsius"

• The lower fixed point of water is the free#ing point of pure

water ! degrees Celsius"



• $ixed points are used as reference points to determine

temperature of other substances

). *se of a thermometer to its desin

H ighlight design features which make a thermometer suitable

for its particular task:

• %ensitivity

&ange

'ortability

(urability

&esponse time

)ase of &eading

Draw and explain design of:

!aboratory Thermometer

%ensitivity- a laboratory thermometer is deined to be sensitive

to chanes in temperature by bein made of very thin lass

which reduces the time ta+en for heat to pass throuh the lass

&ange- it is made usin either mercury or alcohol'coloured(

because alcohol has a rane of ,11) to - derees &elsius and

mercury has a rane of ,#./ to #0.- derees &elsius

'ortability, small and compact therefore easy to move around.

(urability, made with lass which is firm and not damaed bythe heat.

&esponse Time, made with a thin central bore sometimes called

a thread because of its thinness therefore not a lot of the li3uid

needs to be heated to et a rise in temperature.



)ase of &eading, this is ensured by usin mercury which is

briht silver or coloured alcohol

&linical Thermometer

%ensitivity, same as laboratory thermometer e%cept it has an

indentation in the bore to prevent mercury from oin bac+

into the bulb

&ange, 20 to )0 derees &elsius

'ortability, same as laboratory thermometer

(urability, same as laboratory thermometer &esponse time, same as laboratory thermometer

)ase of reading, same as laboratory thermometer

Thermocouple Thermometer

This is two different very thin conduction wires joined at the ends

to create two junctions, this instrument wor*s off the concept of

resistance or voltage change resulting in temperature change

%ensitivity, it can detect e%tremely small temperatures

&ange, it has an infinite ran because it is a comparison

and it can detect very hih temperatures of hundreds of

4elvin

'ortability, not very portable bul+y however it allows

remote temperature ta+in. (urability, very durable the wire is very stron 'metals(

and the meter isn5t in direct contact with whatever is bein

measured



&esponse Time, very fast response time because the metals

are ood conductors of heat.

)ase of &eading, the meters are easy to read because it is

easy to read the analo and diital meters. 6owever it isdifficult to convert the voltae or resistance to temperature

PART 2

'1.1( Thermal energy is what we call energy that comes from heat.

+hen heat is given to a substance, its si#e usually increases. n other

words the substance expands on heating. Thermal e%pansion is thetendency of matter to change in volume in response to a change in

temperature, through heat transfer .

$or example, a cup of hot tea has thermal energy in the form of *inetic

energy from its particles. +hen you pour some mil* into your tea, some

of this energy is transferred to the particles in cold mil*. The cup of tea

is cooler because it lost thermal energy to the mil*.

+hen a substance is heated, its particles begin moving more and thus

usually maintain a greater average separation. aterials which contract

with increasing temperature are unusual this effect is limited in si#e, and

only occurs within limited temperature ranges. Thermal expansion can

be used in bimetallic strips in thermostats it can also be used in

loosening nuts and bolts. A thermometer wor*s by using the thermal

expansion of a li/uid to measure temperature. A hot-air balloon uses the

thermal expansion of air to generate lift. +hen a solid is heated, its

molecules gain *inetic energy and vibrate more vigorously. As the

vibration become larger, the molecules are pushed further apart and the

solid expands slightly in all directions.

http://en.wikipedia.org/wiki/Volume

http://en.wikipedia.org/wiki/Temperature

http://en.wikipedia.org/wiki/Heat_transfer

http://en.wikipedia.org/wiki/Temperature

http://en.wikipedia.org/wiki/Heat_transfer

http://en.wikipedia.org/wiki/Volume



0n a hot day concrete runway

sections in airport expands and

this cause crac*ing. To solve this

problem we leave small gabs between sections.

0n a hot day concrete bridges

expand. To solve this problem,

we leave small gab at one end

and support the other end with

rollers.

Telephone wire contract on cold

days. To solve this problem, we

leave wires slac* so that they are

free to change length.

0n a hot day railway lines

expand. To solve this problem,

gaps are left between sections of

railway lines to avoid damage of

the rails as they expand in hotweather.

7ome applications that uses the e%pansion of li3uids

A physical chane is an e%ample of thermal e%pansion of a fluid.

The molecules move further apart when heated or closer when

cooled.



1. Thermometers

. The valve shown below operates based on the expansion of the

oil. As the room warms of the oil in the valve expands and pushesthe piston down. This shuts off the flow of hot water. +hen the

temperature drops the valve opens again.

n physics, thermal conductivity often denoted k , λ, or κ " is the

property of a material to conduct heat. %ubstances that allow thermal

energy to move easily through them are called conductors. etals are

good conductors of thermal energy.In crystalline materials the phase and crystallite si8e are important.

In porous solids the thermal conductivity heavily relies on void

fraction pore si8e and the fluid contained in the pores.

http://en.wikipedia.org/wiki/Physics

http://en.wikipedia.org/wiki/List_of_materials_properties

http://en.wikipedia.org/wiki/Heat_conduction






+ater is a poor conductor of heat. )ven though when you heat water in a

pan it gets hot /uic*ly....... it still is a poor conductor of heat, because the

force of attraction between the particles is not as strong as those in solids

and the particles move freely about the li/uid. 2ence, when heat is passed through the li/uid, it ta*es a longer time for the particles to

collide with one another and passing the heat energy to the other

particle.

PART )

79!I$7 !I:*I$7 A;$ <A7=7

There are three states of matter3

• %olids

• 4i/uids

• 5ases

7olids have particles that are held together firmly and uniformly and aretightly pac*ed. %olids are also incompressible and have high density.

This is due to strong intermolecular forces. %olids are non-fluid because

the molecules are in a rigid, closely bonded state. These molecules with

vibrate in place. %olids also have a definite shape and volume.

!i3uids have particles that are held together but less tightly, strongly

and uniformly than solids. n li/uids, the intermolecular forces are

strong enough to *eep the particles together, but not in fixed positions.6ecause of the loose bond, li/uid molecules are able to flow. 4i/uids

have a definite volume but not a definite shape. They ta*e the shapes of

their containers.



<ases have particles that move freely. This is because the

intermolecular forces of gases are very wea*. 6ecause of this, gases are

the most fluid. 5ases have no definite shape or volume and therefore

will fill and ta*e the shape of its7 containers.

4inetic Particle Theory

This theory explains the properties of the different states of matter. The

particles in solids, li/uids and gases have different amounts of energy.

They are arranged and moved in different ways.

7olids,

1. 7olids have fi%ed shapes and are non,fluid> This is because the

particles cannot move from place to place.

. 7olids are incompressible> The particles are close together and have

no space to move into.

!i3uids,

1. !i3uids are fluid and ta+e the shape of their containers> The

particles can move around each other.

. !i3uids are incompressible> (espite fluidity, the particles are still

to close and have no space to move into.

<ases,

1. <ases are fluid and fill their containers> The particles can move

/uic*ly and in all directions.. They are compressible> The particles are far apart and have space

to move into.



PART 0

').1( &onduction

n physics, thermal conductivity often denoted k , λ, or κ " is the

property of a material to conduct heat. %ubstances that allow thermal

energy to move easily through them are called conductors. etals are

good conductors of thermal energy.

In crystalline materials the phase and crystallite si8e are important.

In porous solids the thermal conductivity heavily relies on void

fraction pore si8e and the fluid contained in the pores.

+ater is a poor conductor of heat. )ven though when you heat water in a

pan it gets hot /uic*ly....... it still is a poor conductor of heat, because the

force of attraction between the particles is not as strong as those in solids

and the particles move freely about the li/uid. 2ence, when heat is

passed through the li/uid, it ta*es a longer time for the particles tocollide with one another and passing the heat energy to the other

particle.

').2( &onvection

Convection is the transfer of thermal energy from one place to another

by the movement of fluids e.g. air or water".

!and and 7ea ree8e>

(uring the day, the sun heats up both the ocean surface and the land.

2owever, water heats up much more slowly than land and so the air









above the land will be warmer compared to the air over the ocean. The

warm air over the land will rise throughout the day, causing low pressure

at the surface. 0ver the water, high surface pressure will form because of

the colder air. To compensate, the air will sin* over the ocean. The windwill blow from the higher pressure over the water to lower pressure over

the land causing the sea bree#e.

At night, the roles reverse. The air over the ocean is now warmer than

the air over the land. The land loses heat /uic*ly after the sun goes down

and the air above it cools too. The ocean, however, is able to hold onto

this heat after the sun sets. This causes the low surface pressure to shift

to over the ocean during the night and the high surface pressure to moveover the land. This causes a small temperature gradient between the

ocean surface and the nearby land at night and the wind will blow from

the land to the ocean creating the land bree#e.



Radiation

').)( (escribe experiments to investigate the factors on which

absorption and emission of radiation depend

Texture of surface rough, smooth" -

8ature of surface shiny, dull" - 0btain a hot piece of metal with two

different surfaces. 0ne shiny, one dull. 'lace a thermometer at each end

at e/ual distances from both surfaces. easure the temperature at each

end.

&esult3 the end with the dull surface has a higher temperature.

Conclusion3 the dull surface emits radiation at a faster rate heat leavesthe metal more /uic*ly through the dull surface.

Colour of %urface blac*, white" - 0btain two drin*ing glasses and place

a piece of white paper around one and a piece of blac* paper around the

other. 2alf fill each glasses with tap water of the same temperature.

'lace each glass beside each glass under the hot sun and leave them for

exactly two hours. t is recommended to do this at noon when the sun is

high and hot. After two hours, place a thermometer in each glass and

measure the temperature of the water.

&esult3 The glass covered in white has a lower temperature than the one

covered in blac*.



Conclusion3 The white paper reflects the light and hence the lower

temperature of water. The dar* paper absorbs the light and traps it and

hence the higher temperature. (ar* colours are good conductors of heat

and will /uic*ly transfer the heat to the water.

Area of %urface - 0btain two table mats. 0ne should be a few

centimetres thic*er than the other. 'lace identical bowls of hot water on

each mat. easure the temperature of the water at intervals in order to

identify which bowl is losing water faster.

&esult3 The bowl with on the thinner mat loses heat faster because the

matter has a smaller surface area.

Conclusion3 2eat flow through the thic*er mat is slower because the

surface area is larger due to increased thic*ness.

').( &elate the principals of thermal energy transfer conduction,

convection, radiation" to the design of device.

The green house effect facilitates the growth of plants that need a warm

environment. This is especially the case in cold countries. &adiation

from the sun passes easily through the glass panels of a green house and

is absorbed by the plants and the soil inside. The plants also radiate

energy. This radiation is reflected by the glass panels and traps the

energy inside since it cannot pass through the glass roof. Thus the

temperature inside the green house increases until it reaches a thermal

e/uilibrium suitable for plant growth.

a partial physics breakdown

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