Introduction. Welcome

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1 Introduction Welcome This coursebook has been written from the notes I made 3 years ago when I studied AS Physics, as well as the knowledge I have gained since. It is not a comprehensive textbook explanation of every concept you will cover this year, but rather a quick guide covering everything in the exam syllabus. As long as you understand every concept in this book, you will be heading in the right direction for the exam. If there is something in here that is not quite explained enough, make sure you go to textbooks, look online or ask people until you do understand it. Don t let it go until you are comfortable with everything you could be asked. Having the knowledge, however, is only the first part of preparing for AS physics. If you are comfortable with the concepts, begin on past CIE papers, which you can find online at sites such as. or My personal method for studying the past papers is as follows: Do the past paper, all at once without looking at any notes or help. Anything that I guessed at or didn t know at all, I marked with a star. Mark the paper from the provided mark scheme from the website. I paid careful attention to how the answers were set out and where the marks were allocated. Any places either marked with a star, or where I had got the answer wrong, I wrote out the correct answer. Having marked the paper, I went through it again a day or two later, noting down on refill paper the mistakes I had made. This cemented the correct answer in my mind, and more often than not, I never made that mistake again This collection of every answer I got wrong I kept to revise from immediately prior to the exam, known as my Things Not Known list. Pace yourself so that you do as many of these past papers as possible before the exam. Past papers are in my opinion the greatest tool for revising for AS physics. Ben McArthur 3

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3 Contents Important Definitions & Concepts 1 Physical Quantities & Units 2 Measurement Techniques 3 Kinetics 4 Dynamics 5 Forces 6 Work, Energy & Power 7 Phases of Matter 8 Deformation of Solids 9 Waves 10 Superposition 11 Electric Fields 12 Current of Electricity 13 DC Circuits 14 Nuclear Physics List of Equations Revision Question Answers About Me

4 Scalar Quantity Vector Quantity Displacement Speed Velocity Acceleration Newton s First Law Newton s Second Law Newton s Third Law Linear Momentum Force Principle of Conservation of Momentum Upthrust Couple Equilibirum Work done Internal Energy Effificency of a system Power has magnitude, but no direction has magnitude and direction distance moved from the starting point the rate of change of displacement the speed in a certain direction the rate of change of velocity Every body continues in its state of rest, or of uniform motion in a straight line, unless compelled to change that state by a net force For a body of constant mass, its acceleration is directly proportional to the net force applied to it Whenever one body exerts a force on another, the second exerts an equal and opposite force on the first the product of mass and velocity the rate of change of momentum If no external force acts on a system, the total (net) momentum of the system remains constant. a force opposing gravity in any body in a fluid, due to the pressure difference on the top and bottom of it a pair of forces that produces rotation only a system is in equilibrium if there is no resultant force and no resultant torque. the product of a force and the displacement in the direction of the force the sum of the individual kinetic and potential energies of all the particles in a substance the ratio of the useful work done by the system to the total energy input work done per unit time 6

5 Important Definitions & Concepts Density Pressure Load Extension Elastic Limit Hooke s Law Stress Strain Elastic deformation Plastic deformation Displacement Amplitude Phase difference Period Frequency Wavelength Speed Progressive wave Transverse wave Longitudinal wave The Principle of Superposition mass per unit volume normal force per unit area the force applied to a spring the difference in the extended length of the spring and its unextended length the point beyond where plastic deformation occurs provided that the elastic limit is not exceeded, the extension of a body is proportional to the applied load. normal force per unit area the ratio of the change in length to the original length the deformation is not permanent deformation that is permanent the displacement of a point on the wave from the equilibrium position the maximum displacement of the wave the relative difference in cycle between two waves the time taken for one complete cycle of a wave how many cycles of a wave pass a point in a second the distance between corresponding points on a wave the rate of change of displacement of a certain point on the wave a wave where energy is transferred the direction of oscillation is perpendicular to the direction of motion of the wave the direction of oscillation is the same as the direction of motion of the wave the displacement of the resultant wave at any point is the sum of the displacements of all the individual waves that make it up. 7

6 Diffraction Interference Coherence Electric Field Strength Electric Current Charge Potential Difference Resistance Ohm s Law EMF Kirchoff s First Law Kirchhoff s Second Law Nucleon Number Proton Number the spreading out of waves past a boundary or gap the general term for when two waves interact to produce a resultant wave when two or more waves have the same frequency, wavelength and phase difference. force per unit positive charge, acting on a stationary point charge the flow of charged particles a property of matter that electrons and protons have, affected by electric and magnetic fields. the potential difference between two points is the energy converted from electrical energy to other forms of energy if unit charge was to move between them the ratio of the voltage drop across a conductor, and the current through it for any Ohmic conductor, the voltage drop across it is directly proportional to the current through it the energy transferred by a source from other forms of energy into electrical energy, when it is driving unit charge around a circuit The total current arriving at a junction in a circuit must equal the total current leaving the junction The sum of the potential differences and the EMFs around any closed loop in a circuit must be zero the number of all the particles in the nucleus of the atom the number of protons in the nucleus of the atom

7 1 Physical Quantities & Units In this Chapter Physical Quantities SI Units Derived Units Homogenity of Equations Prefixes Scalar & Vector Quantities Vectors Physical Quantities All physical quantities consist of a magnitude and a unit. For example, a length of 5 is meaningless, whereas a length of 5 metres or 5 millimetres is not. Units therefore denote the type of measurement. They each have an abbreviation, eg millimetres are mm ; Kelvin are K, Newtons are N. SI Units There are many different systems of units, for example the metric and imperial systems. These have different units which have different magnitudes relative to each other. The Imperial unit of length, the foot, has a magnitude equal to cm. For all Cambridge courses, we use the Metric system of units. These are units where the base units are exactly chosen so that they fit together nicely. You ll see why soon. The base quantities and units you need to be familiar with are: Mass: kg Length: m Time: s Current: A Temperature: K Derived Units From the above set of so-called base units, every other unit can be derived, using equations. For example, we know that the equation for speed is speed= distance/ time. Therefore, the units for speed are also metres/second or ms^(-1). Every other quantity (acceleration, force, density, pressure, etc) can be expressed as the product of these 5 base quantities. 9

8 Homogeneity of Equations Using the result shown above, that all quantities can be expressed as the product of the base quantities, and hence the units are also the products of the base units, we can check the validity of an equation. The product of the units on each side should be the same. A simple example is the equation shown above for speed. We know that units are as follows: Speed ms -1 Distance m Time s Therefore the equation speed= distance/time is dimensionally consistent, since ms -1 = m/s. To check that any equation is dimensionally consistent, simply find the overall units of both sides of the equation. They will be the same, if the equation is consistent. Prefixes To deal with a large variation in size of quantities, prefixes can be added to any unit to change its magnitude. For example, it is not practical to measure the diameter of the earth as metres, as much as km. It could even be expressed as Mm. Each successive prefix is 1000 times large or smaller than the prefix before it, making conversion between them simple. Remember to convert back into the base units when doing calculations! The prefixes you need to know are: Pico (p) Nano (n) 10-9 Micro ( ) 10-6 Milli (m) 10-3 Centi (c) 10-2 Deci (d) 10-1 Kilo (k) 10 3 Mega (M) 10 6 Giga (G) 10 9 Tera (T)

9 6.0N y Scalar and Vector Quantities As if to make it more confusing, as well as having units, any quantity can be either scalar or vector. The difference between these is simple: Scalar quantities have magnitude only, and no direction. Examples would be mass, density, time. Vector quantities have both magnitude and direction. These are quantities such as force, distance, acceleration. x 30º 4.0N When you write down a vector quantity, it is good practice to include the direction. For example 5 km northwest or 10 N upwards Vectors Scale: 1cm 1.0N reultant, R θ Vectors are the mathematical way to represent vector quantities. You should be studying simple vectors in AS maths so I won t go into too much detail. You need to be able to manipulate vectors in two ways: Add and Subtract Coplanar Vectors To add vectors, simply draw the vectors out, with the correct size and direction, and position them so that the tip of one is at the tail of the other. You ll only need to add together two vectors. 6.0N 4.0N In the example (left), there are two forces on the line XY. The size and direction of the resultant force is found by vector addition. 30º Represent a vector as two perpendicular components Just as two original vectors can be resolved into one overall vector, one original vector can be split up into two. This is useful because a vector of any angle and size has a certain size in the y direction, and a certain size in the x direction. To resolve any vector into these perpendicular components, draw a right angled triangle with the vector as the hypotenuse (longest side). The other two sides of the triangle should be horizontal and vertical. Then use trigonometry to find out the length of each side. These components can be treated as completely separate quantities, which comes in handy later on with kinematics. Original vector Vertical Component Horizontal component 11

10 Revision Questions 1. What two parts are all physical quantities made up of? 2. Name the five base units 3. Explain how homogeneity of equations can be used to check whether equations work 4. Describe the necessary parts of a graph 5. State the full name and power of 10 that the following prefixes represent: p M T c d K n G m 6. State the difference between scalar and vector quantities, giving examples of each 7. Describe how to add and to subtract coplanar vectors This section is mostly a lot of stuff that is common sense, but I ll go over it in case you don t have any. 12

11 2 Measurement Techniques In this Chapter Calibration Curves Errors Precision & Accuracy Measurement Techniques You need to be able to use and describe the techniques for measurement of different quantities. Length can be measured by a ruler, vernier scale or micrometer screw gauge depending on the size of the length. Volume for a regular solid can be found by multiplying its dimensions. For an irregular solid, measuring the volume of liquid displaced. Angle is typically measured using the handy old protractor. Mass is measured usually by first finding the weight, for example using a spring or balance, and then using the equation mass= (weight)/(acceleration due to gravity). The acceleration due to gravity on the earth s surface is 9.81 ms-1. Time using stopwatches or CRO s (more on those later) Temperature using a thermometer Electrical quantities using voltmeters and ammeters. Voltage Time A CRO is a cathode ray oscilloscope, which displays like a graph the variation of a quantity with time. This can be used to find a quantity such as the period of a wave. A galvanometer is an instrument which is very sensitive to the movement of electrical current. It can display both positive and negative current, and is often used to find the point where the current is zero. Calibration Curves Calibration curves hardly ever come up in the exams. They are basically used to relate the variation of one quantity with another. Resistance For example, a resistor might be used to measure temperature. The resistor would be held a certain temperatures, and the resistance for each temperature recorded and plotted on a graph. Then, when the resistor is placed in an unknown temperature, the temperature can be worked out from the resistance and the calibration curve. Temperature 13

12 Errors There are two kinds of errors you need to know about in this course. Systematic Errors are errors made which are the same in every measurement. They are commonly made through an error in technique or a problem with equipment. For example, a ruler that was 1 cm too short would give a systematic error in all its readings of -1 cm. Random Errors are made simply through the random fluctuation of the things being measured, and other variables that are not exactly controlled. For example, it is not possible to line a ruler up with a mark exactly perfectly, and so a random error is introduced around that. Precision and Accuracy Precise, not accurate Precision is how closely repeated measurements of the same quantity agree. It can be thought of as the number of decimal points the quantity is measured to, and is regardless of whether the measurement is correct or not. Accuracy is how close the measurements are to the true value. Finding Compound Uncertainty Finding compound uncertainty is something which is not too hard, and simply requires practice. It s easy, as long as you follow these rules: Accurate, not precise For addition and subtraction, add the actual uncertainty For multiplication and division, add the percentage uncertainty Percentage uncertainty is found by dividing the uncertainty by the original amount measured. Revision Questions Precise and accurate Explain the difference between random errors and systematic errors Explain the difference between precision and accuracy 14