Physics P1 - Conservation of Energy PDF

Physics P1 – Conservation and Dissipation of Energy Energy Store Description System Change Decreasing Increasing Energy Stores Energy Stores Calculating Energy Store Ch...

Physics P1 – Conservation and Dissipation of Energy Energy Store Description System Change Decreasing Increasing Energy Stores Energy Stores Calculating Energy Store Changes Kinetic Energy The energy stored by objects that are moving Tennis Ball Kinetic Gravitational Equations to Remember: Projected Potential Upwards Note, work done and all forms of energy have Gravitational The energy stored in A vehicle slowing Kinetic Thermal the unit Joules, J. Potential Energy objects raised above down ground Work done = Force x Distance W = F x s A battery Chemical Kinetic, Thermal Chemical Energy The energy stored in powered drill is Force in Newtons, N. fuels, food and batteries turned on Distance in metres, m A person sliding Gravitational Kinetic, Thermal Kinetic Energy = ½ x mass x speed2 down a zip-wire Potential Ek = ½ x m x v2 Thermal Energy The energy stored by hot objects Mass in kilograms, kg Speed in metres per second, m/s Power Elastic Potential The energy stored by Gravitational Potential Energy = mass x Power is defined as the rate at which energy is transferred, gravitational field strength x height Energy stretched or squashed or the rate at which work is done. Ep = m x g x h objects An energy transfer of 1 joule per second is equal to a power Mass in kilograms, kg of 1 watt. Height in metres, m g in Newtons per kilogram, N/kg A system is an object or group of objects. Two motors lift the same mass. g = 9.8 N/kg on Earth – you don’t need to A higher power motor will lift the mass recall this. Conservation of energy: in a shorter time. In a closed system, energy cannot be created A lower power motor will lift the mass Energy = Power x Time or destroyed. The total energy is constant. in a longer time. E = P x t In all system changes, energy is dissipated so Power in Watts (W) that it is stored in less useful ways (wasted Time in seconds (s) energy). Dissipated energy usually ends up a Efficiency thermal store in the surroundings. Equations You are Given: The efficiency of an energy transfer can be calculated These unwanted energy transfers can be using: Elastic Energy = ½ x spring constant x reduced using, for example, lubrication (to extension2 reduce friction) or insulation (to reduce the Efficiency = Useful Energy Output or Useful Power Output Ee = ½ x k x e 2 rate of thermal energy transfer). Total Energy Input Total Power Input Spring constant in Newtons per metre, N/m Efficiency has no unit. Extension in metres, m  Combined P2 – Energy Transfer by Heating Energy transfer by conduction Specific heat capacity Specific Heat Capacity Required Practical The higher the thermal conductivity of a material the The specific heat capacity of a substance Aim: Determine the specific heat capacity of one or higher the rate of energy transfer by conduction across is the amount of energy required to raise more materials the material. the temperature of one kilogram of the substance by one degree Celsius. Independent Variable: Material Rate: The speed at which something happens Dependent Variable: Thermal conductivity is a measure of how well a material NOTE: the equation is given to you on Energy input using a Joule meter conducts energy when it is heated. the Physics data sheet Temperature change using a thermometer Mass of the block using a balance Change in thermal energy = mass x specific heat capacity x change in temperature Equation: c = ΔE ÷ (m x Δϴ) ΔE = m x c x Δϴ Equipment Δ = change in ΔE = change in energy Reducing the rate of energy transfers at home m = mass Δϴ = change in temperature The energy transfer per second through a layer of insulation material depends on: Change in energy in Joules, J Mass in kilograms, kg The temperature difference across the material. The Specific heat capacity in Joules per larger the temperature difference the higher the rate kilogram per degree Celsius, J/(kg°C) of energy transfer by conduction. Change in temperature in degrees Celsius, °C The thickness of the material. The thicker the Method material the lower the rate of energy transfer by Rearranging the equation: 1. Measure the mass of the block using a balance conduction. 2. Measure the starting temperature of the block c = ΔE ÷ m x Δϴ using a thermometer. The thermal conductivity of the material. 3. Switch on the powerpack and increase the c = ΔE ÷ (m x Δϴ) temperature of the block using an immersion Ways to reduce energy Reducing the cost of heater loss in homes producing energy in the 4. Measure the energy input using a Joulemeter. home Example: What is the specific heat 5. Record the end temperature and calculate the Loft insulation Energy efficient boiler capacity of 2kg of a material when 4000J temperature difference. changes the temperature by 3°C? 6. Use the equation to find the Specific heat Cavity wall insulation Install solar panels capacity of the block. ΔE = m x c x Δϴ Double glazing 4000 = 2 x c x 3 Improvements Draft excluders 4000 = 6c Wrap the block in insulation to minimise heat loss ÷6 ÷6 to the room 667 = c Repeat investigation and calculate an average to Insulation traps the air in small pockets, reducing the reduce random error rate of energy transfer via conduction c = 667 J/(kg°C)  Combined Science P3 – Energy Resources Energy Resources Environmental Issues Reliable Uses of energy resources include: Different environmental impacts are cause by energy resources: A reliable energy resource is one Transport where we can predict how much energy Electricity Generation Fossil Fuels it will produce in a set time period. Heating When burned (combustion) fossil fuels release carbon dioxide, which is a greenhouse gas. Many renewable energy resources are For example: Greenhouses gases increase global warming, which causes extreme not reliable because they depend on Coal is used for electricity generation. weather events, rising sea levels and damage to species. the weather. For example, wind, solar. Gas is used for heating and electricity generation Combustion of fossil fuels also releases sulfur dioxide, which causes acid rain. Patterns and Trends in Energy Use Petrol is used for transport Wind power is used for electricity generation Renewables Demand for power varies by time of Renewable resources can cause damage to habitats and species when day and season. the land is cleared to build them. Renewable and Non-renewable Nuclear Fuel A renewable energy resource is one that is Nuclear power produces radioactive waste that needs to be stored being (or can be) replenished as it is used. underground for hundreds of years. This means that they won’t run out. Science can teach us about environmental issues but cannot always Renewable energy resources include: deal with the problems because of political, social, ethical or The Sun (using solar panels or heaters) economic considerations. Some power stations are always on, Wind (using wind turbines) they include nuclear & coal. Wave (using water waves) Tidal (using the flow of the tides) Energy Resource Renewable Reliable Emits Carbon Power stations that can be turned on Geothermal (using hot rocks below Earth’s Dioxide quickly include gas and hydroelectric. surface) They can be turned on when needed. Hydroelectric (using the flow of water Fossil Fuels No Yes Yes down a dam) Biofuel (burning biomass from plants or Nuclear Fuel No Yes No Evaluate means to give advantages animal waste) and disadvantages Biofuel Yes Yes Yes Wind Yes No No Always say whether a resource is renewable, reliable and emits carbon Hydro-electricity Yes Yes No dioxide first. Non-renewable resources include fossil fuels and nuclear. One day they will run out. Geothermal Yes Yes No Other important points include: Nuclear: an advantage is you get a There are three fossil fuels: The Tides Yes Yes No large amount of energy from a small Coal mass of fuel Oil The Sun (solar) Yes No No Hydroelectric: can be used to store Gas energy Water Waves Yes No No  Combined Science P4 – Electric Circuits Circuit Symbols Circuit Equations Series and Parallel Circuits Charge flow = Current x time Q = I x t Potential difference = Current x Resistance V = I x R Energy transferred = Charge Flow x Potential Difference E = Q x V Charge flow, Q, in Coulombs, C Current, I, in amperes, A In a series circuit: Time, t, in seconds, s Current is the same through each component Potential difference, V, in volts, V The total potential difference of the power Resistance, R, in Ohms, Ω supply is shared between components Energy transferred, E, in Joules, J The total resistance of two components is the sum of the resistance of each component What causes resistance in a wire? Rtotal = R1 + R2 In a parallel circuit: The potential difference across each component is the same For electrical charge to flow through a closed The total current through the whole circuit is circuit there must be a source of potential the sum of the currents through the separate difference. components The total resistance of two resistors is less Current: The rate of flow of electrical charge. than the resistance of the smallest individual An electric current flows when electrons move resistor. Potential difference: The energy transferred to a through a conductor, such as a metal wire. The component by each coulomb of charge that passes moving electrons can collide with the ions in the LDRs and Thermistors through it. metal. This makes it more difficult for the current to flow and causes resistance. The The greater the resistance of a component the longer the wire, the more collisions and so the smaller the current for a given potential difference higher the resistance. across the component. The resistance of an LDR (light dependent resistor) decreases as light intensity increases. LDRs are Resistance increases as current increases. used in turning on streetlights. Resistance increases as temperature increases. The ions in the metal filament vibrate more The resistance of a thermistor decreases as the as temperature increases. So they resist temperature increases. Thermistors are used in the passage of electrons more. thermostats.  Combined Science P4 – Electric Circuits Resistance of a wire Required Practical I-V Characteristics Required Practical I-V Characteristics Required Practical Results Aim: Investigate factors affecting the resistance Aim: Investigate I-V characteristics of a variety Ohms Law: The current through a resistor at of electrical circuits including the length of a wire of circuit elements constant temperature is directly proportional to at constant temperature and combinations of the potential difference across it resistors in series and parallel. Independent Variable: Circuit component Independent Variable: Length of wire Dependent Variable: Current and potential difference Dependent Variable: Current and potential difference to calculate Control variables: resistance Temperature Control variables: Thickness of wire Equation: V = I x R I-V Characteristics for a fixed resistor (linear) Wire material Temperature Equipment The resistance of a filament lamp increases as the temperature of the filament increases Equation: V = I x R Equipment Method I-V Characteristics for a Filament Bulb (non- Set up the circuit as per the diagram with the linear) component to be tested as a Fixed Resistor. Set the power supply to 2V. The current through a diode flows in one Close the switch and record the current and direction only. The diode has a very high Method potential difference on the ammeter and resistance in the reverse direction. Set up the circuit as per the diagram with a voltmeter. 10cm wire. Repeat for a range of potential differences, by Set the power supply to 2V adjusting the variable resistor. Close the switch and record the current and Reverse the direction of the power supply and potential difference on the ammeter and repeat the experiment. voltmeter Plot a graph of potential difference vs current. Repeat for 20cm,30cm,40cm and 50cm. Repeat for a Bulb and diode. Calculate the resistance for each length using the equation R=V/I Plot a graph of Resistance vs Length of wire. I-V Characteristics for a Diode  Combined Science P5 – Electricity in the Home Alternating and direct current Live wire: Brown: Equations for Applicance Power and Energy The live wire carries the alternating A battery is a dc (direct current) supply. A direct potential difference from the supply. Potential Energy transferred = Charge Flow x Potential potential difference causes the current to flow in difference between the live wire and earth is 230V. Difference one direction only. E = Q x V The live wire is dangerous. Touching the live wire and making a connection to earth causes a person Energy transferred = power x time to be electrocuted, which can be fatal. E = P x t Power = potential difference x current P = V x I P=VxI V=IxR Mains electricity is an ac (alternating current) supply. An alternating potential difference causes P=I x R xI current to periodically reverse its direction. Power = Current2 x Resistance P = I2 x R Neutral wire: Blue The neutral wire completes the circuit and has Charge flow, Q, in Coulombs, C a potential difference of 0V Current, I, in amperes, A Time, t, in seconds, s Earth wire: Green and yellow stripes Potential difference, V, in volts, V The earth wire has a potential difference of 0V. Resistance, R, in Ohms, Ω The mains supply has a frequency of 50Hz and has a It only carries a current if there is a fault. The Energy transferred, E, in Joules, J supply potential difference of 230V. earth wire is a safety feature. Power, in Watts, W Electrical power is transferred from power stations to Step down The amount of energy an appliance transfers is consumers using the national grid. Step up transformers transformers dependent on how long the appliance is switch on increase the potential difference in the transmission lines. decrease the for and the power of the appliance. potential difference A high Potential difference to a safer voltage for The power of an appliance is related to: means a low current use in homes. The potential difference across it and the Low current means less current through it energy is lost through The energy transferred in a given time. heating the wire, so is a more efficient way to transfer energy. For Details on how Step up and Step down transformers work see Chapter 15 Knowledge The national grid is a system of cables and transformers linking power stations to consumers organiser  Combined Science P6 – Molecules and Matter Density of Materials Changes of State Internal Energy 𝑚 Density is defined by the equation: 𝜌= Energy is stored inside a system by the particles 𝑉 (atoms and molecules) that make up the system. This Density, ρ in kilograms per metre cubed, kg/m3 is called internal energy. Mass, m in kilograms, kg Volume, V in metres cubed, m3 Internal energy is the total kinetic energy and potential energy of all the particles that make up a system. 1 kg = 1000 g 1 m3 = 1 x 10-6 cm3 Heating changes the energy stored within the 1 cm3 = 1 ml system by increasing the energy of the particles. Changes of state are physical changes because This either raises the temperature or produces a Particle Model the material recovers its original properties if change of state. Solids, liquids and gases can be represented: the change is reversed (unlike chemical changes). Specific Latent Heat Mass is conserved in a change of state. The energy needed for a substance to change state is called latent heat. The energy supplied changes the internal energy but not the temperature. The specific latent heat is the amount of energy needed to change the state of 1 kilogram of a In a solid, particles are arranged in rows and vibrate substance with no change in temperature. about a fixed position. E =m x L In a liquid, particles are closely packed but not arranged in rows. E = energy for a change of state in Joules, J m = mass in kilograms, kg In a gas particles are in constant random motion. L = specific latent heat in Joules per kilogram, J/kg Gases have a low density because there are large Specific latent heat of fusion: gaps between particles. change of state from solid to liquid Specific latent heat of vaporisation: Particle Model and Pressure change of state from liquid to gas The higher the temperature of the gas, the higher the kinetic energy of the particles and the faster they move. Increasing the temperature, at constant volume, increases the pressure as when particles move faster, they collide with the walls more often.  Combined Science P6 – Molecules and Matter Density Required Practical – Use appropriate apparatus to make and record the measurements needed to determine the densities of regular and irregular solid objects and liquids. The methods below go into more detail for each of the three objects – regular and irregular solids, and liquids. Each method has similarities – measure the volume, measure the mass, then calculate density. A regular solid object is one where the volume An irregular solid object is one where the volume To measure the density of a liquid, we need to be can be calculated from the dimensions. For cannot be calculated from the dimensions. For careful that we do not include the mass of the example, a cube or cuboid. example, a pebble or chess piece. container holding the liquid. C For the method below, the container is a A measuring cylinder. Steps Steps Steps B 1. Measure the mass of the object using a 1. Measure the mass of the object using a balance. 1. Measure the mass of a measuring balance. cylinder using a balance. 2. Fill a displacement can with water. 2. Measure the length of the sides of the object using a ruler. 2. Add a set volume of liquid such as 20 ml. 3. Carefully drop the irregular object into the displacement can. 3. Measure the mass of the cylinder 3. Calculate volume, by multiplying the three side with the liquid in it, using a balance. lengths together. E.g. A x B x C 4. Measure the volume of water that leaves the can, using a measuring 4. Calculate density using: cylinder. This is equal to the volume of the irregular object. 4. Subtract the mass of the empty cylinder to get the mass of liquid. 𝑚 𝜌= 5. Calculate density using: 𝑉 5. Calculate density using: 𝑚 𝑚 𝜌= 𝜌= 𝑉 𝑉  Combined Science P7 - Radioactivity Atomic Structure: The Nuclear Model Nuclear Radiation Four types of radiation can be emitted from the nucleus: Alpha, beta, gamma and neutrons. Atoms are very small, with a radius of about 1 x 10-10m. The structure of an atom is: What is it? Absorbed Range Ionising Example Decay By in air Power The centre of Alpha 2 protons, 2 Skin About High 219 215 + 42𝐻𝑒 86𝑅𝑎 → 84𝑃𝑜 the atom is α neutrons Paper 5cm called the (helium nucleus) Alpha decay causes the mass and nucleus. charge of the nucleus to decrease. Beta High speed Thin About Medium 14 14 0 β electron aluminium 1m 6𝐶 → 7𝑁 + −1𝑒 Beta decay doesn’t change the mass but the charge of the nucleus increases Most of the mass is in the nucleus. Gamma Electromagnetic Thick Infinite Low Gamma ray emission does not change The radius of the nucleus is 1 / 10000th the γ radiation lead the mass or charge of the nucleus radius of the atom. The electrons are arranged at different distances from the nucleus, in energy levels. The Development of the Model of the Atom Half Life Radioactive decay is random Electrons can move away from the nucleus Before the discovery of the electron, atoms were thought The half-life is the time it takes for the count (higher energy level) by absorption of to be tiny spheres that couldn’t be divided. rate, activity, or number of radioactive nuclei electromagnetic radiation. of an isotope to fall to half its initial value. Electrons can move closer to the nucleus (lower After the discovery of the electron, scientists suggested energy level) by emission of electromagnetic the plum pudding model. The atom is a positive ball. radiation. Can you describe - - The half-life differences with - Electrons are for this Atoms can be represented as: the nuclear model? - embedded in it isotope is 25 years. Mass Number 12 6𝐶 The results from the alpha particle scattering experiment led to the discovery of the nucleus. This led to a new Atomic Number model, the nuclear model. All the mass and positive The count rate or number of nuclei remaining charge is thought to be in the nucleus. after n half-lives can be calculated by dividing The atomic number is the number of protons. the initial value by 2n. (Higher Tier Only) The mass number is the total number of protons Niels Bohr adapted the nuclear model by adding electron and neutrons (number of things in the nucleus). orbits. Bohr’s calculations agreed with experiments. Hazards Alpha, Beta and Gamma are ionizing, which In an atom there are the same number of protons 20 years after the nucleus was accepted as an idea, means they can remove electrons from atoms. and electrons, so atoms have no overall charge. James Chadwick discovered neutrons within it. In our cells this increases the risk of cancer. Atoms can lose electrons to become positive ions. Irradiation is the process of exposing an New experimental evidence may lead to a scientific object to nuclear radiation. Radioactive Isotopes are atoms of the same element that model being changed or replaced. contamination is the unwanted presence of have different numbers of neutrons. radioactive substances on other materials.