physics-igcse (3).pdf

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Department
Information Systems Management
Course
ISMM1-UC 144
Professor
davidjenkins
Semester
Spring

Description
Sp Heat Capacity Q = m X Lf or P t = m x Lf Q = m x c x ∆ t VIt = m X Lf P t = m x c x ∆ t Sp Latent Heat of Vaporisation V I t = m x c x ∆ t Q = m x Lv or Pt = m x Lv Thermal Capacity = m x C Or = Q / ∆ t V I t = m x Lv Sp Latent Heat of Fusion 1 Copyright belongs to the creator and owners. PHYSICS NOTES REVISION. 1.General Physics The use of measuring cylinder for volume 1.1 Length and time The Use of rules to measure length Submultiples of m 1cm=10 m2 1mm=10 m-3 -6 1um=10 m -9 1nm= 10 m 1km=1000 m How measurements are done: Stare directly above a ruler 2 Copyright belongs to the creator and owners. Measuring Time: Instruments are the stop clock or stopwatch 3 Copyright belongs to the creator and owners. 1.2 Speed, velocity and acceleration Speed is the distance travelled in unit time. Speed-time graphs Start to Point A- Constant speed To find distance- find area under graph 4 Copyright belongs to the creator and owners. A to B- Uniform Acceleration- To find acceleration find its slope or gradient Driving away from A is Constant speed Then the body is at rest or not moving EQUATIONS OF MOTION When a (acceleration) is a constant: V=u+at S=(u+v)t/2 V2=u2+2as 2 S=ut+1/2at 5 Copyright belongs to the creator and owners. Accelerationof free fall = Any body falling under the effect of gravity alone will fall down at a constant and uniform acceleration is called acceleration of free fall. Value- 10m/s What is Terminal Velocity? As a body falls from a particular height the air resistance opposing it increases as its speed increases, thus its accelerations falls. Gradually, the air resistance increases and eventually its value will match the value of the object’s weight or gravitational force. (Air resistance=Weight) The resultant force is zero so the body will travel at a constant velocity called terminal velocity. Value of Terminal Velocity differs. Depends on: weight, size and shape. Example 1: A small dense object. It will have a high terminal velocity as it will travel a longer distance before air resistance equals its weight. Example 2: A light object with larger area It has a low terminal velocity as it will travel a shorter distance before air resistance equals its weight. 6 Copyright belongs to the creator and owners. 1.3 Mass and weight The above beam balance balances when we add an object to one pan and more objects of known mass to the other pan. The balance actually compares the weights i.e. gravitational force on both the pans. Since the pans balance when both weights are equal, the masses should also be equal. So both mass and weight can be compared at the same time using the beam balance. What is mass? 1. It is the amount of matter in a substance. 2. Mass can be related to inertia, which is the resistance of the body or its inability to a change in velocity and motion. What is weight? 1. Weight is the gravitational force of the earth acting on a body. 2. “g” can be of two meanings. Firstly it is the gravitational field strength that is the force of gravity acting on unit mass of a body that is at rest (g=10 kg/N). Secondly it is called acceleration of free fall that is the uniform acceleration of a body falling under effect of gravity alone (g=10 m/s ). Both are denoted by the letter “g”. 7 Copyright belongs to the creator and owners. 1.4 Density Density is defined as the mass per unit volume. 1 g/cm =1000 kg/m 3 Determining density 1. Liquid a. Use a measuring cylinder to find the volume. b. Use a balance to get the mass. c. Use the formula to get the density. D=m/v 2. Regular solid a. Use a ruler to measure the necessary dimensions. Then use correct formula to get the volume. b. Use a balance to get mass. c. Use d=m/v to get the density 3. Irregular solid a. Use a balance to get the mass. b. Pour water to the measuring cylinder. Note initial volume, then add the solid inside and measure final volume. Find the difference between both, which is the volume of the solid. c. Or just use the displacement method. 8 Copyright belongs to the creator and owners. d. Use d=m/v to get the density. 1.5 Forces a)Effects of forces. • Forces acting on an object may cause a change in its size and shape. • A force can change the speed and direction of a moving object. • On force-extension graphs the stretching force is plotted in the y-axis while the total extension on the x- axis. • F=ma To interpret Force-extension graphs: • This shows a spring stretched beyond its elastic limit • Extension means difference between stretched and unstretched lengths • Hooke’s Law applies here. It states that stretching force and extension are both proportional only if the elastic limit is not exceeded. • In the proportional limit, removing the load, returns the spring to its origin length. • Beyond the elastic limit, at any point where we remove the load the spring will not return to its original length. 9 Copyright belongs to the creator and owners. Important points about Hooke’s Law • Extension and stretching force are both proportional to each other as long as the elastic limit is not exceeded. • For force-extension questions use the formula: F=kx • Where “k” is the force constant which can be found from two other readings F and x. X is the extension. Circular motion • Motion along a circular path is Circular Motion. • It is an accelerated motion because velocity keeps changing i.e. direction of speed changes. • This acceleration is called Centripetal acceleration. • The force needed to move an object in a circular path is called centripetal force. • Both centripetal acceleration and force act inwards and towards the centre of the circular path. • The force depends on mass of the mass and speed of the object, and the radius of the circular path. • Different type of forces causes centripetal force on the object: a. Frictional force gives the force between road and tire of the car. b. Tension of the string gives the centripetal force to move a stone in a circle If an object is released from the circular path it will move through the tangent. 10 Copyright belongs to the creator and owners. b) Turning Effect Moment of a force is a measure of its turning effect. It is measured by multiplying the force into the distance from a pivot or fulcrum. Examples include balancing pans in a beam balance. A beam is normally balanced when: 1. The weights on both pans are same. 2. Same mass. 3. Equal distance from the pivot. 4. So in the end the clockwise moment is equal to the clockwise moment. All equilibrium systems follow the Law of moments which says: When a system is in equilibrium the sum of clockwise moment equals the sum of anticlockwise moment about the same pivot. C)Conditions for equilibrium to occur: 1. Sum of the forces in one direction equals the sum of forces in the opposite direction. 2. Law of moments should apply. 11 Copyright belongs to the creator and owners. d) Centre of Mass Centre of mass of a plane lamina(Very important for Paper 6) 1. Make a hole in the lamina. 2. Hang it so it can swing freely. 3. Hang a plumb line in the hole and mark the line it passes through. 4. Repeat the procedure again to get another line 5. Their intersection point is the centre of mass. Stability of simple objects The position of the centre of mass affects its stability. If the centre of mass of an object is low, it is less likely that will tip over if we tilt it. To increase stability we should: 1. Increase surface area 2. Making the object shorter. How to know if an object will not tip over after tilting them? The vertical line through the centre of mashould be within the base. 12 Copyright belongs to the creator and owners. e) Scalars and vectors Difference Scalar Vector Has a magnitude. Has a magnitude. No direction. Direction present. Eg: distance, speed Eg: Force,weight,velocity Resultant of two vectors We should use the Parrallogram law: 1. Give a suitable scale to the forces such as 10 N= 1cm. So 50 N will be 5 cm and 100 N will be 10 cm. 13 Copyright belongs to the creator and owners. 2. Draw the two lines using the suitable scale given with the correct angle in between in graphical form (on paper). 3. Using a compass with 10 cm wide length, place the needle on the point A, and draw an arc. 4. Change the compass to 5 cm and make a 5cm wide length and place it on point B. Draw another arc. 5. Draw a line through point A to the intersection point of the arc. And draw another line through point B to the arc. So now we got acomplete parellogram. 6. Draw the diagonal from the intersection point of the two arcs to the centre of the angle 50 degrees. 7. Measure the diagonal. Convert the length to Newton. That is the resultant force. 8. The direction will be stated as “making an angle X with the force 100 N” 14 Copyright belongs to the creator and owners. 1.6 Energy, work and power a)Energy Kinetic Energy: An energy possessed by a body by the virtue of its motion. 2 K.E= ½ mv Potential energy: An energy possessed by a body by the virtue of its position. P.E=mgh Different forms of energy a) Kinetic energy e) Nuclear energy b) Gravitational potential energy (a f) Internal energy form of potential energy) g) Electrical energy c) Chemical energy h) Light/ heat energy d) Elastic potential energy (a strained i) Sound energy condition of potential energy) 15 Copyright belongs to the creator and owners. Conversion of energy Energy is not lost, but is converted from one form to another. Law of Conservation of energy Energy cannot be created nor destroyed. If it disappears, it converts to another form in which the total energy is still the same. Examples include: 16 Copyright belongs to the creator and owners. b) Energy Resources Renewable and Non renewable resources Renewable sources of energy are natural sources of energy which can be replaced and be used over and over again. Non-renewable sources of energy are natural sources which cannot be replaced and so once using it, there is no more use of it in the future. Obtaining useful forms of energy Fossil fuels- The fuels are burned in a thermal power station which in turns heat up the water in a boiler and turns it to steam. The steam drives the turbines which in turn drives the generator that generates electricity. Chemical energyHeat energyKinetic energyElectrical energy Water-They are used in Hydroelectric power stations. The water is stored behind dams, found in a large water reservoir. When the dam is opened so water moves which rotates a turbine which in turn drives a generator to create electricity. Potential energyKinetic energyElectrical energy Geothermal energy: If water is pumped into the hot rocks down the earth they can be heated to steam. This steam can drive a turbine and in turn allows a generator to generate electricity. Nuclear energy: The radioactive materials are decomposed by nuclear fission and so they release heat that boils water in a boiler. The steam drives the turbine and so electricity is generated by the generator. Nuclear energyHeat energyKinetic energyElectrical energy Solar energy: Solar cells convert light energy directly to electrical energy. Light energyElectrical energy 17 Copyright belongs to the creator and owners. Advantages and disadvantages A. Fossil fuels Advantages: 1. High energy density 2. Ready availability 3. Small size of energy transfer device Disadvantages: 1. Non Renewable 2. Causes air pollution by waste gases CO 2nd SO 2 B. Nuclear fuels Advantages: 1.Ready availability 2.High energy density 3.Does not cause air pollution with CO2and SO 2 Disadvantages: 1. Expensive to build and to decommission 2. Wastes from fuels are very dangerous and will stay reactive for many years. 3. High safety standards are needed. Renewable Resources advantages: They are renewable so it can be replaced. And they do not pollute the atmosphere. Disadvantages: Solar energy: 1. It is not always renewable 2. Low energy density 3. Expensive. 18 Copyright belongs to the creator and owners. Wind energy: 1. Wind is variable. 2. Spoils landscape and is very noisy. 3. It needs a large site to build turbine towers Wave energy: Difficult to build. Hydroelectric energy: 1. Expensive to build. 2. Not all sites are suitable 3. Can damage the environment Geothermal Energy: Difficult and expensive to dig deep inside the earth. Biofuel: Large sites are needed to grow enough plants. c)Work Work is done when a force moves an object through a particular distance. When a work is done energy is being converted to another form. Work= Force x Distance Unit=Joules. 19 Copyright belongs to the creator and owners. e) Power Power is defined as the rate at which work is done. P = E/t 1.7 Pressure Pressure is defined as the force acting on unit area. Lower the surface area, the higher is the pressure. The higher is the surface area, the lower is the pressure. P=F/A Mercury Barometer The mercury barometer is used to measure the atmospheric pressure. It consists of a glass tube placed upside down on a reservoir. The entire device is filled with mercury. It works on the principle that the weight of the mercury should balance the atmospheric pressure. If its weight is less than the air, then it will rise so that it can balance itself with the air pressure. If it is more than the air, its level will reduce. 20 Copyright belongs to the creator and owners. Liquid Pressure Liquid pressure depends on both density and depth inside the liquid. Denser the liquid like oil, has higher pressure than a water. Deep sea divers face more pressure inside the water than when at near the surface. So p=hpg Manometer A manometer is used to measure gas pressure. At first, the liquid levels will be the same, as atmospheric pressure is same. But when we add an extra supply of gas, the pressure will be different. Thus, the liquid will increase by a certain height. So the gas pressure will be= Atmospheric pressure + pressure due to the liquid column AB The pressure on the liquid column AB can be found by the formula hpg. 21 Copyright belongs to the creator and owners. 2.Thermal Physics 2.1 Simple kinetic molecular model of matter (a) States of matter Distinguishing features of solids, liquids, and gases. Property Solid Liquid Gas Molecules are cloLoosely packed, sMolecules are much Packing packed, arranged are slightly furtfarther apart than in regular pattern. apart than in solsolids and liquids. Definite shape No definite shapeNo definite shape. Shape shape of container. Definite volume Definite volume No definite volume Volume Vibrate in its plMoves rapidly pasMoves quickly in all Movement other in short didirections Difficult. Possible but onlyEasy to compress. limit. Compress repulsion both baand repulsion.attwhen molecules arey Forces close. 22 Copyright belongs to the creator and owners. Temperature of a gas As a gas is heated, its molecules will gain energy and they will move faster in all directions. This means that their average speed and kinetic energy increases. So temperature can be said to be the measure of the average kinetic energy of molecules. Pressure of a gas Molecules are in constant and rapid motion in gas, and so they collide with the walls of the container many times a second. So they will exert a pressure by g
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