 # AQA Physics Unit 2

Flashcards by , created about 2 years ago

## Taken directly from the specification, so contains all you need to know for physics unit 2. Good luck for Friday =) 33 4 5  Created by Natalia Cliff about 2 years ago
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 Question Answer What is Newton's third law? Whenever two objects interact, the forces they exert on each other are equal and opposite What is a resultant force? A number of forces acting at a point may be replaced by a single force that has the same effect on the motion as the original forces all acting together. This single force is calle dteh resultant force What effect does a resultant force have? A resultant force acting on an object may cause a change in its state of rest or motion Resultant Forces on Stationary Objects -If the resultant force is zero the object will remain stationary -If the resultant force isn't zero the object will accelerate in the direction of the resultant force Resultant Forces on a Moving Object -If the resultant force is zero the object will continue moving at the same speed in the same direction -If the resultant force isn't zero the object will accelerate in the direction of the resultant force Equation for Acceleration of an Object F=ma Distance Time Graph Distance Time Graph (image/png) How can you find the speed of an object from a distance time graph Gradient of a distance time graph is the speed Velocity Time Graph Velocity Speed Graph (image/png) How can you calculate distance travelled and acceleration from a Velicity Time Graph? -Gradient is the accelaration -Distance travelled is the area under the graph Equation for accelaration a=(v-u)/t What are the forces acting on a vehicle travelling at a steady speed? The resistive forces (mainly air resistance) balance out the driving forces Factors affecting the Braking Force -The greater the speed of th vehicle, the greater the braking force needed to stop it in a certain distance Factors affecting stopping distance Thinking distance (distance the vehicle travels whilst the driver thinks) -Tiredness -Drugs -Alcohol -Distractions Braking distance (distance the vehicle travels under the breaking force) -Bad road conditions (icy roads) -Bad weather conditions (rain) -Bad vehicle condition (breaks and tires) - How do Brakes work? When the brakes of a vehicle are applied, work done between the brakes and the wheel reduces the kinetic energy of the vehicle so the temperature of the brakes increase Friction on a Falling Object The faster an object moves through a fluid the greater the frictional force that acts on it Terminal Velocity -An object falling through a fluid will initially accelerate due to the force of gravity -Eventually the resultant force will reach zero as the increased air resistance balances out the force of the weight of the object -The object is then moving at terminal velocity as it cannot accelerate any more Velocity Time Graph for Terminal Velocity Terminal Velocity (image/jpeg) Changing the Shape of an Object A force acting on an object may cause a change in the shape of the object Storing Elastic Potential Energy A force applied to an elastic object such as a spring will result in the object streching and storing elastic potential energy Hooke's Law Graph and Equation F=ke Hooke's Law (image/gif) What is work done? -When a force causes an object to move through a distance work is done W=Fd -Energy is transferred when work is done What is Power? -Power is the work done or energy transferred in a given time E=P/t What is Gravitational Potential Energy? Gravitational Potential Energy is the energy that an object has by virtue of its position in a gravitational field E=mgh What does Kinetic Energy depend on? The kinetic energy of an object depends on its mass and speed E=(mv^2)/2 What is Momentum? Momentum is a property of moving object P=mv What is the Conservation of Momentum? In a closed system the total momentum before an event is equal to the total momentum after the event How do Objects gain Static Electricity? -When two insulating materials rub against each other they become electrically charged -Negatively charged electrons are rubbed from off one material onto another -The material that gains electrons becomes negatively charged -The material that loses electrons becomes positively charged How do two Electrically Charged Objects react to each other? -When two electrically charged objects are brought together they exert a force on each other -Two objects with the same type of charge repel each other -Two objects that carry different types of charges attract each other What is Electrical Current? Electric current is a flow of electric charge. The size of the electric current is the rate of flow of electric charge I=Q/t Q is Charge in Coulombs What is Potential Difference (Voltage)? The potential difference between two points points in an electric circuit is the energy transferred per coulomb of charge that passes between the points V=W/Q W is work done in Joules Circuit symbols Circuit Symbols (image/jpeg) Thermistors -A temperature dependant resistor -In hot conditions resistance drops -In cool conditions resistance goes up -Make useful temperature detectors Light-Dependant Resistor (LDR) -LDR is a resistor that's dependant on light -In bright light resistance falls -In darkness resistance is high -Used in automatic night lights and Burglar alarms Current-Potential Difference Graphs -Are used to show how the current through a component varies with the potential difference across it Current-Potential Difference Graph for a resistor with a constant temperature Current Potential Difference Graph (image/png) How can you calculate resistance? -Can be found by measuring the current through and voltage across a component -The current through a resistor (at a constant temperature) is directly proportional to the voltage across it V=IR Components Connected in Series -The total resistance is the sum of the resistance of each component -The same current through all components -The total potential difference of the supply is shared between the components Components Connected in Parallel -The potential difference across all components is the same -The total current through the whole circuit is the sum of the currents through the separate components Resistance in a Filament Bulb -The resistance of a filament bulb increases as the temperature of the filament increases -When an electrical charge flows through a resistor, the resistor gets hot Resistance In A Filament Bulb (image/png) Current Through a Diode Current In A Diode (image/gif) LED Lighting -An LED emits light when current flows through it in a forward direction -Becoming more common in lighting as they use a much smaller current than other forms of lighting AC and DC Electricity -Batteries supply current that always passes in the same direction, called DC -Mains Electricity in an ALternating Current (AC) with a frequency of 50 Hz and 230 V in the UK Finding Frequency T=1/f f= $$\lambda$$ / v Structure of a 3 Pin Plug Structure of a cable is very similar, same 3 wires that are all separately insulated and then have one outer insulating cover Plug (image/gif) Dealing with Electrical Faults -If an electrical fault causes too great a current, the circuit is disconnected by a fuse or circuit breaker in the live wire -When the current in a fuse exceeds the rating of the fuse it will melt -The thicker the cable the higher the fuse value -Some circuits are protected by Residual Current Circuit Breakers (RCCBs) -RCCBs work by detecting a difference in the current of neutral and live wires -Appliances with metal casings are usually earthed -Some appliances, however, are double insulated and so don't need to be earthed -The earth wire and fuse both protect the wiring of the circuit What is Power? The rate of energy transfer P=E/t P=IV How are Energy, Potential Difference and Charge related? E=VQ Rutherford and Marsden Experiment -Early model of the atom said that it was a positive sphere with negative electrons in it, like plums in a plum pudding -Fired a beam of alpha particles at a thin gold foil -Expected them to pass through, but some came out at an angle or came straight back -Realised they were being repelled and deflected by a concentrated centre of positive charge Atomic Structure If you really don't know what protons, neutrons, electrons, isotopes and ions are check out the C1 flashcards What are Radioactive Substances? Substances that give out radiation from the nuclei of their atoms all the time, whatever is done with them Where does Background Radiation come from? -Rocks -Cosmic rays from space -Fallout from nuclear weapons tests -Fallout from nuclear accidents What is Radiation made of? -Alpha particles are two protons and two neutrons -Beta particles are one electron -Gamma radiation is electromagnetic radiation Alpha and Beta Decay -When alpha particles are emitted the nucleus loses two protons and two neutrons -When a particle emits beta radiation a neutron in the nucleus turns into a proton Properties of Alpha particles -Highly ionising -Cannot travel far in air (eventually ionises atoms in the air) -Not very penetrating (can be stopped by a hand) Properties of Beta Particles -Moderately ionising -Can travel moderately far in water -Can be stopped by a few mm of aluminium Properties of Gamma Particles -Not very ionising -Can travel furthest through air -Most penetrating, can be stopped by a few cm of lead Radiation in Electric and Magnetic Fields -Alpha and Beta particles are both deflected in opposite directions -Beta deflected more, as despite having half the charge of Alpha it has a much smaller mass -Gamma radiation not affected as it has no charge Use and Dangers of Radiation -Alpha Radiation used in smoke detectors, highly ionising but on the ceiling so far away from people -Beta radiation used as medical tracers, as it is less ionising than Alpha -Beta radiation also used in monitoring the thickness of materials -Gamma radiation is used to sterilise medical equipment and treat cancer Half Life -The Half Life of a radioactive isotope is the average time it takes for the count rate from a sample containing from a sample containing a radioactive isotope falls to half it's initial level -Or the time it takes for the number of radioactive nuclei of the isotope in a sample to halve What are the two fissionable substances used in nuclear reactors? -Uranium-235 -Plutonium-239 Process of Fission -For fission to occur, the nuclei must first absorb a neutron -The nucleus then splits into two smaller nuclei and 2 or 3 neutrons, energy is also released -The neutrons may then go on to produce chain reactions -That's why control rods made of Boron can be lowered to absorb these extra neutrons Nuclear fusion -The joining of two atomic nuclei to form a larger on -Stars use this to release energy -Fusion in stars produces all the naturally occurring elements -These elements are distributed throughout the universe by an exploding supernova at the end of it's life cycle Life Cycle of a Star -Stars form when enough dust and gas from space is pulled together by gravitational attraction (smaller masses can also be attracted and form planets) -During the main sequence period of it's life-cycle a star is stable because the forces are balanced - Life Cycle of a Star Life Cycle Of A Star (image/png)