Download - IGCSE SLG and Energy syllabus
Natalie Yu
5.2 know and use the relationship between density, mass and volume
Density, Mass and Volume
High Density Low Density
DefinitionsDensity - The degree of compactness of particles in a substanceMass - A large body of matter with no exact shapeVolume - The amount of space that the object occupies
Formula
Density (kg/m3) Mass (kg) Volume (m3)
All Mass, Density and Volume are proportional. This means that if you increased one of the
sections, the final sum would increase by the same amount. It can also be called as them being
directly proportional.
Video(Density Experiment): http://www.youtube.com/watch?v=B3kodeQnQvU
Experiments to determine density - Hilary Ip
Experiment 1: Finding the density of a regular shaped object eg. A cube
1. First, find the mass of your object by placing it
on an electronic balance. Record the mass.
2. Secondly, find the volume of the object
3. To find the volume you have to multiply the
height, length and width. For example for our cube the
calculation is 2 x 2 x 2. Record the volume
4. Remember, density = vm
5. Calculate the Density from your results.
6. You have found your density
Experiment 2: Finding the density of an irregular shaped object eg. A stone
1. First, find the mass of your object by placing it on an electronic balance Record the mass
2. Secondly, find the volume of the object. To find the
volume of the object there are two ways.
● You could use a displacement can. Fill the
displacement can up to the spout opening. Tie a string
around your object. Hold a measuring cylinder at the end of
the spout. Carefully lower the object in to the displacement
can. The volume of water that ends up in the measuring
cylinder is the volume of the object.
● You could also just use a measuring cylinder
if it fits. Place the object in a known volume of water (V1).
Measure the new volume of water (V2). Subtract the old
volume from the new volume: V2 –V1 = Volume of object.
3. Density = vm
4. Calculate the Density from your results.
5. You have found your density
Force, Area and Pressure
There is a relationship between force, area and pressure. It is shown in the
triangle on the left, where F is Force (N), A is Area of contact (m2) and Pressure
(Pa) To find out what one of them is, you must know the other two. The equation
are as follow: Force= Area x Pressure, Area= Force/Pressure and
Pressure in a Liquid - Janet Cheng
Pressure in a
liquid can be
calculated by
multiplying the
density of liquid,
the height of
water above the
object and the
gravitational field.
Remember that
the calculated pressure in a liquid is the additional
pressure to the atmosphere. The pressure of the
atmosphere is around 100,000 Pascals.
An object submerged under water has pressure
exerted from all directions.
Test yourself!
What is the pressure on a deep sea diver 110 m below thesurface of the sea? (Let the density of seawater be the sameas water, take g = 10 ms2)
5.8 understand that molecules in a gas have a random motion andthat they exert a force and hence a pressure on the walls of thecontainerThe random movement of gas particles shows that kinetic energy ispresent. When the container volume increases, the pressure will go downbecause there is more area for the gas to spread out. When the volumedecreases, the pressure will increase because there is less space. Themore the amount of particles, the more often collisions per unit area, whichwill increases the pressure since there is more force.
Title –Gas molecules expert pressureGas molecules travel in a random motion in a space,
and when they collide which other particles they exert a force. An exampleof this is that gas particles collide with the surface of a balloon, thepressure they exert keeps the balloon inflated since there is pressureinside the balloon. The more often the particles collide, the greater theexerted force.
VacuumThe metal ball experiment is an experiment where air inside the ball ispumped out, which means there is no pressure since it creates a vacuuminside the ball, thus no atmospheric pressure. It is nearly impossible toopen since the air pressure presses the two hemispheres together, whilethere is no pressure inside to equal out the air pressure.
Alan Sou
5.9 Understand why there is an absolute zero of temperature which is –273°C.Cynthia
Absolute zero is the lowest temperaturepossible, at 273°C or 0K on the Kelvinscale. Absolute zero is when there is a totalabsence of energy, and particles onltgyhave minimal vibrational motion.
Absolute zero is impossible to go below,
because there is only so much energy you
can remove. Once all that energy has been removed, that is the point which we define as absolute
zero.
5.10 describe the Kelvin scale of temperature and be able to convert between the
Kelvin and Celsius scales - Alex LiWhat is Kelvin?
Kelvin is the SI base unit for thermodynamic temperature, and uses absolute zero as its nullpoint (absolute zero / 273°C = 0 Kelvin).
Convert to CelsiusTo convert to Celsius, add 273.When converting, the 0.15°C can be ignored.
Kelvin + 273 = CelsiusCelsius 273 = Kelvin
Examples of conversion0 K = 273°CAbsolute Zero = 273°C273.15 K = 0°C1 K = 272°C1 °C = 272 K
Did you knowAbsolute zero is actually 273.15°C, but inIGCSE Physics we ignore the 0.15°C
5.11 understand that an increase in temperature results in an increase in
the average speed of gas moleculesLink between Kinetic energy, speed and temperature
Speed of Molecules
As you know from Brownian motion, gas molecules are constantly vibrating and
colliding with each other. The SPEED of the collision is decided by its Kinetic
energy.
The amount of kinetic energy is determined by its TEMPERATURE. Therefore, the
higher the temperature, the more kinetic energy, resulting in an increase of the
average speed of gas molecules.
5.12 describe the qualitative relationship between pressure and Kelvin
temperature for a gas in a sealed container
T
Boyle’s LawBoyle’s Law is a principle which describes the relationship between pressure and volume of agas
For a fixed mass of gas at a constant temperature,the pressure is inversely proportional to the volume.P is inversely proportional to 1/vEquation: P1V1=p2V2
Boyles Law is only true if: (EXAM FAVOURITE)1. The mass of the gases are the same2. The temperature is the same
Features:1. If the volume halves, the pressure doubles2. Pressure x volume always has the same value3. If pressure is plotted against 1/volume, the graph is a straight line through the
origin.EG.
A gas has a pressure of 100kPa of a volume of 10cm3. The volume is changed to 5cm3. Findit’s new pressure.
P1V1= P2V2P2= P1V1/V2= 100x10/ 5= 200kPa (kilo pascals)
4.3 understand that energy is conserved Energy cannot be destroyed norcreated; it is conserved.
The law of conservation of energy states that
in an isolated system, the total energy cannot
change – it cannot be destroyed nor created.
However, energy can change forms. In otherwords, it just means that energy can betransferred from different types of energy,for example electrical energy to kinetic energyor gravitational potential energy to thermal
and sound energy.An example of this is in the diagram below. The ball on the top has 1000J of GPEenergy and 0J of KE. Can you figure out what the KE of the ball is in the exactmoment before it hits the ground? It is actually fairly simple. The GPE energy istransferred into KE, so the KE is 1000J. This proves that energy is transferred andconserved but not destroyed.
4.6 Describe how energy transfer may take place by conduction, convection and radiation
By Kessandra and Olivia :3
Heat can be transferred in 3 ways: conduction, convection and radiation.
ConductionEverything is made up of particles that vibrateconstantly. When something is heated, theparticles near the hotter area vibrate faster. As aresult, the faster moving particles collide with theslower moving particles causing the heat energy tobe transferred to the slower moving particles. As aresult, the slower moving particles begin thevibrate faster. This process continues and heatenergy transfers to other areas. This process isknown as conduction.
Conduction can only happen in solids, liquids or gases and cannot occur in vacuums such as space.Metals are good conductors of heat and non-metals and gases are usually good insulators.
ConvectionWhen a fluid is heated, the part near the heatedarea has a higher temperature. As a result, thatarea becomes less dense and the particles in theheated area rises. The particles in the cooler areasinks to the bottom. The new, cooler particles alsogain energy and as a result, they rise too. Thehotter particles at the top have cooled down andsinks back down under the force of gravity. Theprocess repeats itself. This process is known asconvection and the cycle is known as a convectioncurrent.
Convection can only happen in liquids or gases (fluids) and cannot occur in vacuums and solids.
RadiationEnergy transferred by radiation is known as thetransfer of energy through electromagnetic waves.When an object absorbs the electromagnetic wave,the energy carried by the waves transfers to theparticles in the object. As a result, the object’stemperature rises.
Radiation can happen in vacuums, like space, whichis how Earth gets its heat from the Sun.Lesson aims – To understand activities of
convection in everyday life
4.7 – Role of convection
Convection occurs in everyday life. Whenyou boil water heat convects to the airaround us. Air and liquids convect. Hotteratoms become less dense and go up whilecooler ones sink down.
You sometimes turn on theair-conditioner in summer. Convectionoccurs when hot air rises as it vibratesmore and becomes less dense and allowsless dense air to sink.Fireplaces seem to heat the house byconvection but were proven wrong. Hotair rises and the heat from the smoke issucked up from the chimney. Sometimes,you feel that your back is cool when yousit in front of a fireplace – the air is suckedin by the fireplace. The only effectivemethod that fires heat you is radiation!
When you boil water and measure thetemperature of the container, the lowersection of it is often a few degrees lowerthan on the upper half of the container.This is because convection flows andforces hot water (less dense) to rise.
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4.8 explain how insulation is used to reduce energy transfers from buildings andthe human body.By: Joyce Chung
Insulation
Because air is a bad conductor of heat, insulators in buildingsusually contain pockets of trapped air to stop heat from beingconducted away. The wall cavities of these structures are usuallyfilled with an insulator such as polystyrene foam (it is sometimesalso coated with silver material to reflect infra-red radiation), andcarpets can be used to trap heat. Windows can also reduce energytransfers from buildings if they are double glazed. This is as theyhave a gap in which trapped air is held, so they reduce thermal
energy transfer through them.
On the other hand, the humanbody manages to reduce thermal energy transfer through thewearing of clothes. If they are made out of wool, it is particularlyeffective as it is made out of tiny fibres that trap heat betweenthem. The skin also manages to insulate heat through the raisingof hair follicles, although this may not be as useful.Because conduction is being reduced by poor conducting materialand radiation in buildings are being stopped by things reflectingheat, these methods are successful as convection is not a problemin a solid structure. The human body also has similar principles.
4.10 understand that work done is equal to energy transferred
Work done is equal to the energytransferred The work done is equal to energy transferred as seen in the Equation for power:
POWER = ENERGY TRANSFERRED/TIME
or WORK DONE/TIME
For example, when you walk up the stairs, If your Work done (FxD) is
40J then the energy transferred is also 40 J. This is because on earth, energy
cannot be destroyed or created, it can onlytransferred into a different form of energy.
Gravitational potential energy (4.11 - know and use the relationship :
GPE = mgh)
Gravitational potential energy is a type of stored energy. It is the energy a certain mass has
gained. The three factors that affect it is the mass and height of the object, as well as the
gravitational field strength (On Earth its 10).
If an object is raised above the ground, it gains gravitational potential energy. Remember, GPE
is always given in Joules as it is a form of energy.
To calculate GPE:
Change in GPE (joules) = Mass (kg) x Gravitational Field Strength (N/kg) x Height (m)
GPE = mgh
Example:
On Earth, a ball of 0.5kg is kicked straight up. How much GPE does it have
at its highest point 6m of the ground?
Answer:
The ball has a mass of 0.5kg, the maximum height is 6m and the
gravitational field strength is 10 (On Earth).
GPE = 0.5 * 6 * 10
= 12 joules
By: Aaryam Srivastava
4.12 know and use the relationship:
kinetic energy = 1/2 × mass × speed2
Kinetic EnergyKinetic energy is a type of energy which is stored in an object. A classic example
of this is an object which is rolling with speed. If an object has a mass and is
rolling in speed and we can calculate the kinetic energy of that object by the
following formula:
KE=½mv2
From this formula, we can figure out the relationship between mass, velocity and
kinetic energy. It goes as thus:
If v goes up by x number of times, then the KE (kinetic energy) will go up by 4x.
Example:
A ball is rolling on the ground at 20m/s. It has a mass of 100kg. Find it’s kinetic
energy.
KE=½mv2
KE=½ x 100 x 202
KE= 20000J
Extension:
GPE at start= KE at end
ONLY IF THE FOLLOWING IDEAS ARE TRUE:
1. Energy is conserved
2. Air resistance is negligible
Example:
A ball is falling towards the table and at the start it has a GPE of 10J. When the
ball is 1 atom spaced away from the table, its GPE is going to be 0J, and all the
energy is transferred into KE.
This also means that:
GPE top= KE bot
½mv2=mgh
½v2=gh
v2=2gh
v=(2gh)1/2
4.13 Understand how conservation of energy produces a link
between gravitational potential energy, kinetic energy and
work
Link between GPE, KE and work – Justin YimGPE, as you can see from the diagram, is
mass x gravitational field strength x
height. KE, is ½ x mass x velocity
squared. Another important thing to
remember is the law conservation of
energy which states “energy cannot be
created of destroyed, it just changes
forms”. There is a link between
gravitational potential and kinetic
energy which is, gravitational potential
energy at the top is equal to kinetic
energy just before reaching the ground.
This is because no energy can be lost or
created and there is only one
transformation made which is GPE into
KE. The law of conservation of energy
can also provide a link between GPE and
work where the amount of energy
needed to lift something up is equal to
its GPE. The same goes for work and KE
where you throw a ball and the energy
needed to throw the ball is equal to its
kinetic energy.
POWER: in terms of energy transfer and work done
Power=energy transfer/time taken
· “Power” is the amount of energy something can transfer in a given period of time
· The units for power are watts (W) and joules per second (J/s)
· E.g. A washing machine has 2000 watts. This means that it uses 2000 joules per
second.
Jake Smith 10R06M
4.16 - Energy Transfers in Electricity GenerationHuman beings use many methods to convert raw energy to more usable forms. Some of thesemethods are more technologically advanced, while others have been used for a long time. Most ofthese methods result ultimately in the generation of electrical energy. Energy in this form is usefulfor many different appliances, ranging from household air-conditioning to powerful roboticmachinery.Energy cannot be destroyed nor created. Therefore, electricity is just another form of the energypresent before the transferring processes. For example, wind is harnessed to generate electricity.The kinetic energy of the wind drives a turbine which causes electron movement. This movement isbasically electricity. Likewise:
Hydroelectrical: gravitational potential (water at the top of a dam) à kinetic (water flows downwards)à mechanical (turbines spin) à electrical energy
Wave: kinetic (waves move air) à mechanical (turbines spin) à electrical energy
Tidal: kinetic (tides) à mechanical (turbines spin) à electrical energy
Geothermal: thermal (heat from earth heats up water) à mechanical (turbines spin due to pressure) àelectrical energy
Solar cells: light (from Sun) à electrical energy (electrons in solar panels move)
Solar heating: light (from Sun) à thermal (water is heats up)
Fossil fuels: chemical potential (from decomposed remains) à thermal (fuel is burned to heat water)à mechanical (turbines spin due to pressure) à electrical energy
Nuclear: nuclear (from atoms) à thermal (water is heated up) à mechanical (turbines spin due topressure) à electrical energyOf course, some of the energy is unavoidably wasted during these processes, in forms such as sound.However, it is evident that all of these processes can provide energy for humans to use, with varyingdegrees of efficiency.