The Ultimate IGCSE Physics Guide.docx

1、The Ultimate IGCSE Physics GuideThe Ultimate IGCSE Guide to PhysicsBy CGPwnedUnit 1: Solids, Liquids and GasesDensitySO whats density? Well, all solids, liquids and gases have different properties and characteristics. One such characteristic is density. Solids are often very dense, liquids are less

2、dense than solids, and gases have very low densities. Density is how much mass something has for a certain volume in other words, how squashed up something is.To calculate density, use this equation:Density = Mass/VolumeP = m/vExample: A piece of iron has a mass of 390kg and a volume of 0.05m3. What

3、 is its density? P = m/v P = 390kg/0.05m3 = 7800kg/m3 Remember the unit! Density can be kg/m3, g/cm3etcCalculating Volumes for the DensityFor a cuboid like this, simply multiply its length, width and height. Im assuming you know this, but if not, work up your maths manAs for irregular solids, measur

4、e out a certain amount of water with a measuring cylinder. This is the control (something to compare results to). Do the same with another measuring cylinder, and drop the solid in. Note the rise in the level of water. The difference between the two measurements is the volume of the solid, in this c

5、ase, 10ml.PressurePressure in SolidsLets start like this: You can easily push a pin into a piece of wood quite easily, but it is pretty much impossible to make a hole in the wood with your finger. You can try with little success (and end up with splinters all over your fingers). Why is that? The sma

6、ll point of the drawing pin concentrates all your pushing force into a tiny area, so the pin goes into the wood easily.To get to the point, pressure is defined as the force per unit area. Force is measured in newtons (N) and area is measured in square metres (m2). The unit for pressure is N/m2 or Pa

7、 (for Pascals).Unfortunately, there is an equation that comes with pressure and this is ONLY FOR SOLIDS:Pressure (in Pascals) = Force (in newtons)/Area (in square metres)p = f/aExample: A woman weighs 600N and the total area of her shoes in contact with the ground is 0.0015m2. Find the pressure she

8、is exerting to the ground.p = f/a p = 600N/0.0015m2 = 400000Pa (or 400kPa)Pressure in Liquids and GasesPressure in liquids act equally in all directions as long as the liquid is not moving. This is the same for gases. The pressure in air is a staggering 100000Pa, but since the pressure inside our bo

9、dies are similar, we dont feel the pressure. The pressure in air is also referred to as 1.0 atmosphere.To calculate pressure in liquids use the following equation:Pressure (in Pa) = Height/Depth (in m) x Density (in kg/m3) x Gravitational Field Strength (in N/kg)Or p = hdg Note that g is usually 10N

10、/kgvExample: Justin Biebers (oh my god!) swimming pool has a depth of 3m. What is the total pressure of the swimming pool? Take the gravitational field strength to be 10N/kg and the density of water to be 1kg/m3 (ignore the swimming pool being chlorinated cause JBs swimming pool is always clean anyw

11、ays). p = hdg (the actual equation is p=hpg, but Im not bothered finding that special p for density) p = 3m x 1kg/m3 x 10N/kg p = 30PaThe Brownian MotionBrownian Motion: The continual random movement of microscopic particles. When particles collide into one another, this causes a change in speed and

12、 direction of the particles, making them randomly move about. Boyles LawThis is all summarized into the following equation:Pressure1 x Volume1 = Pressure2 x Volume2Or p1V1 = p2V2Example: Atmospheric pressure is 100kPa. Some air in a sealed container has a volume of 2m3 at atmospheric pressure. What

13、would be the pressure of the air if you reduced its volume to 0.2m3? 100kPa = 100000Pa P1V1 = p2V2 100000Pa x 2m3 = p2 x 0.2m3 200000 = 0.2p2 P2 = 1000000Pa = 1000kPaAnd in wordsBoyles Law: At a constant temperature and with a fixed mass of gas, pressure is inversely proportional to volume.Question:

14、 How does a gas exert a pressure on the walls of its container?Billions of tiny air particles move about in continual random motion. Particle collisions with the walls of the container exerts a force, which gets distributed over the area of the wall of the container, hence, exerting a pressure. Pres

15、sure LawTemperature also has an effect on the pressure of a gas. This is shown in an experiment set up on the right. When water is heated gradually, the air is also heated, changing the reading on the pressure gauge. Plot down the results and youd get a graph that looks something like this.Wait a mi

16、nuteshouldnt the pressure be at zero pascals? No. This is because pressure is NOT proportional to temperate in Celsius. But what happens if you continue cooling the gas? Youd find that when pressure is zero, the temperate would be at -2730C. This temperate is known as absolute zero. When converted t

17、o kelvins (another type of measurement for temperature), absolute zero is zero kelvins. But back to the point, what would happen if you converted the temperatures into kelvins?Converting between Kelvins and CelsiusKelvins = Celsius + 273Celsius = Kelvins 273If you convert the temperatures into kelvi

18、ns, this is what happens:There is a positive correlation! This shows that pressure of gas is proportional to temperature in Kelvin. This leads into the Pressure Law equation: (Note that temperatures must be in Kelvin)Pressure1/Temperature1 = Pressure1/Temperature1Or p1/T1 = p2/T2Example: You take an

19、 empty tin and put the lid on tightly. You heat it using a Bunsen burner until the temperature of the air inside is 500C. What is the pressure of the air inside the tin? The temperature of the room is 200C and atmospheric pressure is 100kPa.We must first convert the temperature in Kelvin, so: T1 = 2

20、0 + 273 = 293K (This is the temperature OUTSIDE the tin) T2 = 50 + 273 = 323K (This is the temperature INSIDE the tin)p1/T1 = p2/T2100kPa/293K = p2/323Kp2 = 110kPaNow to summarise the Pressure Law:Pressure Law: With a fixed mass of gas at a constant volume, pressure is proportional to temperature (i

21、n Kelvins).States of MatterSolidsLiquidsGasesParticles are closely packed.Regular structure.Vibrate about fixed positions.Particles are closely packed.Irregular structure.Random motion within structure.No fixed positions.Move at rapid random motion.Are very spread out.Change in States of MatterUnit

22、2: EnergyWhat the hell is energy? Well, energy is used everywhere! We need to use energy to walk, to life objects, to push, to pull, and in most cases, to think. Machines also need to use energy to power up. Thats why your iPod cant last forever without electricity! We get our energy from food and i

23、t is then transferred into other forms of energy such as kinetic energy and heat energy. What the hell are you talking about? Well you will find out later.Define Energy: Energy is the ability to do work.Types of Energy and Energy ConversionsThis table summarises some of the different types of energy

24、 that you will need to learn about in GCSE.EnergyDescriptionChemicalEnergy that is stored in food or batteries. We burn it into other forms of energy.ThermalAlso known as heat energy. Most energy is wasted by turning into this. We use thermal energy to keep ourselves warm.SoundAlso a possible form o

25、f waste energy. But Im sure you know what sound is. It is a series of longitudinal waves but well get to that later.LightThis energy emits a light. We need light to see things. Things like light bulbs have energy that is converted to this.ElectricalMost of the energy we need is converted from electr

26、ical energy. Electrical energy can be made from other forms of energy.Gravitational PotentialStored energy that varies depending on where you are. The higher, the more.KineticAlso known as movement energy. Electrical energy is converted to kinetic energy to make motors work. We get this from chemica

27、l energy.GeothermalEnergy from the heat underground stored in the Earths core. This is found in volcanoes and thermal springs.Elastic PotentialEnergy that is stored in springs. This type of energy is found in catapults and bows.Nuclear EnergyThe energy released when unstable uranium atoms in the nuc

28、lear reactor break down and form a chain reaction.Energy is converted in different ways. Here are some examples:When we run, chemical energy from our food is converted to kinetic energy. Some of it is wasted by being converted into thermal energy, making us hot.When a vibrator is used, chemical ener

29、gy from the battery is converted into electrical energy, which is then converted into kinetic energy. Some is wasted through sound energy.EfficiencyEnergy will never disappear. It can only be wasted or converted into other forms of energy. Physicists believe that the amount of energy in the Universe

30、 is constant which means we cannot use energy up.This leads us to the Law of Conservation of Energy.The Law of Conservation of Energy states that:Energy is not created or destroyed in any process. It is just converted from one type to another.Drawing Sankey DiagramsWhen we are considering energy tra

31、nsfers, we must remember that a proportion of the energy input is wasted. Real systems can never have 100% efficiency. The useful output energy will always be less than the input. Efficiency is given in percentage usually anyway, but read the question for the specific unit.This is a Sankey diagram.H

32、ow does it work? Well the Sankey diagram always points right. The input energy is written at the beginning of the arrow, with the amount of energy specified in joules. Then the arrow splits into more arrows. The arrow that goes straight right is the useful energy (which needs to be stated too). The arrow pointing down is wasted energy.W