Flashcards in gcse_physics_aqa_9-1_20180320143540 Deck (286):
When energy is transferred to an object, the energy is....
Stored in one of the object's energy stores e.g. kinetic energy store etc.
Kinetic energy is...
Thermal energy is...
The hotter the object, the more thermal energy
Chemical energy is...Example?
Anything that can release energy by a chemical reaction e.g. Food
Gravitational potential is...
Any object raised above ground level
Elastic potential is...Example?
Anything stretched e.g. springs, rubber bands
Example of electrostatic energy...
Two charges that attract or repel eachother
Example of magnetic energy...
E.g. Two magnets that attract or repel each other.
Nuclear energy is...
The nucleus of an atom releases energy from this store in nuclear reactions
4 ways energy can be transferred:
Mechanically, Electrically, By radiation, By heating.
Mechanically transferred energy happens when...
A force does work.
Electrically energy transferred happens when...
When a moving charge does work.
Energy can be transferred by heating - this is when...
Energy is transferred from a hotter object to a colder object.
Energy can be transferred by radiation - this is when...
Energy is transferred by e.g. Sound or light.
When a system changes...It can be transferred...
Energy is transferred. It can be transferred into or away from the system between different objects in the system or between different types of energy stores.
What is a system?
A single object or group of objects that your interested in.
What are closed systems?What is the net change like?
Where no matter or energy can enter or leave. The net change in the total energy of a closed system is always zero.
When a closed system changes...
There is no overall change in the total energy of the system.
Conservation of Energy Principle:
Energy can be transferred usefully, stored or dissipated but can never be created or destroyed.
When a system changes...
The energy is simply MOVED between stores. (Never disappears)
Is energy that is dissipated/wasted gone ?
No. It has just been transferred to an energy store that we didn't want.
What causes mechanical energy transfers?
2 points about Work Done:
What is the energy in an objects Kinetic Energy Store?The energy in the Kinetic Energy Store depends on...
Movement.The object's mass and speed - the greater its mass and the faster it's going, the more energy in the Kinetic Energy Store.
When an object speeds up, what happens to the energy?
It is transferred to the kinetic energy store.
Formulae for finding object's kinetic energy store:Units?
E = 1/2 x mass x speed (v) squared.Mass units - kgSpeed units - Minuites / secondsEnergy - joules
Formulae to find Gravitation Potential energy:Units?
E = Mass X gravitation field strength (9.8n/kg) x heigh Mass unit - kgHeight unit - m
Energy lost from the gravitation potential store = ?
Energy gained in the kinetic energy store (this is for a falling object when there's no air resistance)
Formulae to find elastic potential energy store:
E = 1/2 x Spring constant x extension squared.Spring constant unit - n/mExtension unit - m
What is specific heat capacity?
The amount of energy needed to raise the temperature of 1kg by 1 c. Basically, how hard it is to heat something up - some materials need more energy to be transferred to their thermal energy stores in order for their temperatures to increase.
The amount of energy stored or released as a material changes temperature depends on...
The specific heat capacity of the material.
Formulae for change in thermal energy:
Give the 9 steps to investigating the specific heat capacity of a SOLID BLOCK:
1) measure the mass of the block.2) wrap it in an insulating layer to reduce energy losses (e.g. thick newspaper)3) set up the apparatus. (connect ammeter and power supply to the insulation)4) measure the starting temperature of the block.5) turn on the power supply and start a stopwatch.6) record potential difference of the power supply and the current - they shouldn't change.7) after 10mins take a reading of the block's temprature.8) turn of the heater and work out the temprature change.9) work out the power using the equation.
What 3 things do you need before measuring specific heat capacity?
1) calculate the power.2) calculate the energy transferred.3) find the change in temperature.CALCULATE.
What is POWER?
The rate of energy transfer - the rate of doing work. Power is how fast energy is transferred.
What is power measured in?
One WATT =
1 joule of energy transferred per second.
Give the 2 equations you can use to calculate power:
1 POWER = ENERGY TRANSFERRED DIVIDED BY TIME.2POWER = WORK DONE DIVIDED BY TIME.
Explain how USEFUL energy is formed:
When energy is transferred between stores, some energy is transferred to the stores you want it in. USEFULLY TRANSFERRED.
What does it mean if energy is 'dissipated'?
This means the energy is transferred to useless stores which is often called 'wasted' energy.
Useless energy stores are usually....
Thermal energy stores.
There are ways you can reduce the amount of energy wasted.Explain how LUBRICATION REDUCES FRICTIONAL FORCES.
Friction acts between all objects that rub together which causes some energy to be dissipated. Lubricants reduce the friction between them which reduces the amount of dissipated energy.
There are ways you can reduce the amount of energy wasted.Explain how INSULATION helps.
When part of a material is heated - that part gains energy which is transferred across the material so the rest gets warmer. KNOWN AS CONDUCTION.Insulation has a low thermal conductivity so less transfers happen.
How quickly a building cools depends on: (3)
1) how thick the walls are - the thicker the walls the slower the building will cool.2) the thermal conductivity of the walls. Building walls from a material with a low thermal conductivity reduces the rate of cooling.3) how much thermal insulation there is - loft insulation reduces energy losses through the roof.
The less energy that is wasted, the more...
efficient the energy transfer is.
The efficiency of an energy transfer is a measure of....
The amount of energy that ends up in useful energy stores.
What are the 2 equations for efficiency:
Efficiency = useful output energy transferred DIVIDED BY total input energy transfer.Efficiency = useful power output DIVIDED BY total power input.
What are nonrenewable energy resources? Common ones?
Resources that will run out one day. The main ones are fossil fuels and nuclear fuel.
What are renewable energy resources?
Resources that will never run out because they can be replaced as quickly as they are being used.
Give the seven renewable energy resources:
1) SUN 2) WIND.3) WATER WAVES.4) HYDRO ELECTRICITY.5) BIO FUELS.6) TIDES.7) GEOTHERMAL.
Transport uses both renewable and nonrenewable energy resources. Give an example of each:
NON RENEWABLECoal is used to steam trains to boil water to produce steam.RENEWABLEVehicles can run on pure bio fuels or a mix of a bio fuel and petrol or diesel.
Electricity can also be used for transport. Give an example:
Electric cars and some trains.
Nonrenewable and renewable energy resources are needed for heating things. Give two examples of each:
NON RENEWABLECoal is burnt in open fireplaces.Gas fires burn natural gas to heat rooms.RENEWABLEElectric heaters can use electricity from renewable sources.Bio fuel boilers work in the same way as gas boilers.
State how wind turbines work: (2)
1) Placed in open spaces.2) When the wind turns the blades, electricity is produced.
Give two advantages of using wind turbines:
1) they produce no pollution once they are built.2) they do no permanent damage to the landscape because once they are removed the area goes back to normal.
Give two disadvantages of wind turbines:
1) they don't produce electricity when the wind stops.2) it is impossible to increase the supply when there is extra demand for electricity.
Where do you solar cells generate electricity from?
Directly from the sunlight.
Give two advantages of solar cells:
1) they create no pollution once they are built.2) in sunny countries they are very reliable.
Give two disadvantages of using solar cells:
1) A lot of energy is used to build them.2) The only generate electricity during the day.
Where does geothermal power get their energy from:
They use energy from the thermal energy stores of hot rocks below the Earth's surface. Used to generate electricity or to heat buildings.
Give 2 advantages of using geothermal power:
1) very reliable because the hot rocks are always hot.2) only a small impact on the environment.
How does hydroelectric power work?
It involves building a big dam across a valley, the valley is usually flooded and water is allowed to flow out through turbines which generates electricity.
Give two advantages of using hydroelectric power:
1) there is no pollution when it is running.2) there is no problem with reliability in countries that get rain regularly.
Give two disadvantages of using hydroelectric power:
1) animals and plants lose their habitats.2) there is a big impact on the environment due to the flooding of the valley.
How does wave power work to generate electricity?
Turbines are on the coast of turned by water waves and the electricity is generated.
Give one advantage of using wave power:
There is no pollution.
Give two disadvantages of using wave power:
1) they disturb the seabed and the habitats of animals.2) they are quite unreliable as the waves tend to die down when the wind drops.
How do TIDAL BARRAGES generate electricity?
Tidal barrages are big dams with turbines in them built across rivers. Water passing through the turbines generates electricity.
Give two disadvantages of using tidal barrages:
1) fish are killed as they swim through the turbines.2) they change the habitat of the wildlife e.g. Birds and sea creatures.
Give two advantages of using tidal barrages to generate electricity:
1) no pollution.2) they are reliable because we can predict the tides.
What are biofuels?
Fuse created from plant products or animal dung. They can be burnt to produce electricity in the same way as fossil fuels.
Give two disadvantages of using biofuels:
1) they release carbon dioxide when they're burnt.2) large areas of forest have been cleared to make room to grow biofuels so a lot of animals have lost their habitats.
Give two advantages of biofuels:
1) crops can be grown throughout the year.2) extra biofuels can be constantly produced and stored for when they are needed.
Give three ways in which nonrenewables create environmental problems:
1) fossil feels release carbon dioxide into the atmosphere when they are burnt which leads to global warming.2) coal mining makes a mess of the landscape.3) Oil spills cause environmental problems and harm sea creatures.
How have people began to use more renewable energy resources? (2)
Pressure from other countries and the public has meant that governments have set targets for using renewable resources.Car companies have began to be more eco friendly.
Moving to renewable energy sources can be limited by money, give 2 examples of this:
1) building new renewable power plants costs money.2) cars that run on electricity are more expensive than petrol cars.
Moving to renewable sources can also be affected by politics, people and ethics. Give two examples of this:
1) the cost of switching to renewable power will have to be paid through energy bills or taxes. (People)2) many people also did not want to live near to a power plant like a wind farm or hydro electric dam.
In real life, how does air resistance act against all falling objects?
It causes some energy to be transferred to other energy stores e.g. the thermal energy stores of the object and surroundings.
Explain what energy is useful and what energy is not with the example of a phone:
Phone = system. Energy is usefully transferred from the chemical energy store of the battery in the phone. Some of this is dissipated and energy is transferred to the thermal energy store of the phone.
Explain what energy is useful and what energy is not with the example of a cold spoon:
Cold spoon dropped in an insulated flask of hot soup which is sealed. The flask is a perfect thermal insulator so the spoon and soup form a closed system. Energy is transferred from the thermal energy store of the soup to the useless thermal energy store of the spoon (causing soup to cool down slightly) = energy transfers have occured but net change of energy is ZERO.
A poweful machine is one which....
Transfers lots of energy in a short space of time.
Heating can occur by...
Conduction and Convection.
Conduction takes place in...
Solids - especially Metals.
How does Heating by Conduction take place in solids?
It causes the particles to vibrate more and collied with eachother and during these collisions, energy is transferred between the particles' kinetic energy stores.
What is Thermal Conductivity?
A measure of how quickly energy is transferred through a material in Conduction.
Materials with a high thermal conductivity transfer...
Energy berween their particles at a higher rate.
Convection takes place in...
Gases and liquids - not solids.
What happens during Convection?
The warmer and less dense region (heat) will rise above denser, coolder regions. Energetic particles move away from hotter to cooler regions.
What happens to the particles during Convection?
An area is heated so the particles move even faster and the space between the particles increase. This causes the density of the region being heated to decrease.
Explain how Draught Excluders are an example of Thermal Insulation:
They are around doors and windows and reduce energy transfers by convection.
Explain how Double Glazed Windows are an example of Thermal Insulation:
They have an air gap between two sheets of glass to prevent energy transfer by conduction through the windows.
Explain how Loft Insualtion is an example of Thermal Insulation:
They reduce convection currents in lofts which is where the air particles are constantly heated, rising, cooling and then sinking.
Explain how Cavity Walls are an example of Thermal Insulation:
They are made up of an inner and outer wall with an air gap in the middle. The air gap reduces the amount of energy transferred by conduction through the walls.
Explain how CAVITY WALL INSULATION is an example of Thermal Insulation:
It is when the cavity wall air gap is filled with a foam which also reduces energy transfer by convection in the wall cavity.
How can you improve the efficiency of energy transfers? (3)
Insulating objects, lubricating them or making them more streamlined.
No device is...
100% efficient and most useless energy is transferred to the thermal energy stores.
What is the only exception to the idea that no device is 100% efficient?
Electrical heaters as all the energy in the electrostatic energy store is transferred to "useful" thermal energy stores.
Give 2 ways Bio-Fuels could create Environmental Problems:
Name the 3 states of matter:
What 4 differences between the states of matter does the particle model explain?
1) particles of a certain material are always the same no matter what state.2) particles have different amounts of energy in different states.3) forces between particles are different in each state.4) particles are arranged differently in different states.
Give 3 facts about SOLIDS:
1) particles are held close together by strong forces in a regular fixed pattern.2) the particles don't have much energy.3) can only vibrate around a fixed position.
Give 3 facts about LIQUIDS:
1) the particles are held closed together in an irregular pattern.2) particles have more energy than the particles in a solid.3) they can move past eachother in random directions at low speeds.
Give 3 facts about GASES:
1) the particles aren't held close together. NO FORCES.2) particles have more energy than in liquids and solids.3) particles constantly move around in random directions at a range of speeds.
Do gas particles bump into eachother and the sides of the container they're in?
When gas particles hit something what happens?
They apply force to it.
What is pressure?
The force applied over a given area.
What happens when you increase the temperature of a Gas?
You increase its pressure.
The temprature of a gas depends on :
The average energy in the kinetic energy stores of the gas particles.
The hotter the gas, the higher the....
If particles have more energy in their kinetic stories they.......
The hotter the gas the faster the particles.......
Move on average.
Faster particles hit the sides of the container more often. What does this so?
It increases the force on the container.
Increasing the temperature of a gas increases........any exceptions?
It's pressure. ONLY IF the space the gas takes up (volume) doesn't change.
What is Density?
A measure of how much mass there is in a certain space.
Equation to work out density:Units?
P = MASS DIVIDED BY VOLUME(P = density kg/m cubed)Mass - kgVolume - m cubed
The density of an object depends on..........
What it's made of and how it's particles are arranged.
What are the particles in a dense material like?
Particles are packed tightly together.
What's denser?SOLIDS or LIQUIDS?
What's Denser?LIQUIDS or GASES?
4 steps to find the density of a regular shaped object:
1) use a balance to measure the mass.2) measure it's length width and height with a ruler.3)calculate the volume.4) find density.
7 steps to finding the density of a irregularly shaped object:
1) use a balance to measure mass.2) fill a eureka can with water.3) place a measuring cylinder under the spout.4) put object in water.5) the volume of water that the spout has it equal to the volume of object.7) find density.
4 steps to find the density of a liquid:
1) place a measuring cylinder on a balance and zero the balance.2) pour 50ml of the liquid into the cylinder.3) record the liquid's mass shown on the mass balance.4) find density.
What is 1 ml equal to?
What is 1 cm cubed equal to?
0.000001 m cubed.
What is Internal Energy?
The total energy stored by particles in a system.
What kind of energy do atoms and molecules have?
Kinetic energy storePotential energy store
The internal energy of a system is......
The total energy that all its particles have in their Kinetic and potential energy stores.
One thing that increases Internal Energy:
Heating. It transfers energy to its particles.
Heating a system may lead to......
A change in tempratureOrA change of state
How much the temprature of the internal energy is depends on........ (3 things)
The mass of the system, it's specific heat capacity and how much energy is transferred to it.
When does a change of state happen?h
When particles have enough energy in their kinetic energy stores to break the bonds holding them together.
Does mass change in a change of state?
A change of state is a physical change not a chemical change.What does this mean?
You don't end up with a new material, the particles are just arranged differently.
Does the number of particles change when the state changes?
What happens if you reverse a change of state?
It will get back all the properties it had before the change.
GAS TO LIQUID?
LIQUID TO SOLID?
SOLID TO LIQUID?
LIQUID TO GAS?
Boiling / evaporating
SOLID straight to a GAS?
What changes and what doesn't change in a change of state?
INTERNAL ENERGY CHANGES.TEMPERATURE DOESN'T.
Heating a material transfers energy to the material. What could this do?
It either increased the temprature of the material OR changes it's state.
When a material cools, the energy is.......
Transferred away from it.
What forms when a material condenses or freezes?What does this cause?
Bonds form. This causes energy to be released. INTERNAL ENERGY DECREASES.
What is Specific Latent Heat?
The energy needed to change the state of a 1kg mass.
What is the energy transferred during a change of state called?
For heating, latent heat is.......
The energy gained to cause a change of state.
For cooling, latent heat is........
The energy released by a change in state.
FORMULA FOR SPECIFIC LATENT HEAT:
ENERGY (J) = MASS (kg) X specific latent heat (J/kg)
Specific latent heat has different names for different changes of state:What is it called for:Solid to liquid Liquid to gas
Solid and a liquid = specific latent heat of fusionLiquid and a gas= specific latent heat of vaporisation
GAS straight to a SOLID?
The internal energy of a system/material is.....
The kinetic energy and potential energy it's particles have as they move.
In a gas, increasing the temprature gives the particles......
More energy and they move around faster.
The temprature of a system depends on both how much.....
Energy it has and how much mass it is made from.
In any state, heating the particle increases their.....This can increase the.......
internal energy.temprature of the material or cause it to change state.
When a material is changing state, it's......
temprature doesn't change.
If we put more particles into a container with gas particles, what would happen?
The pressure will increase because there are more collisions with the sides of the container.
Give 2 rules when drawing a circuit diagram:
1) make sure all the wires in your circuit are straight lines.2) make sure the circuit is closed.
Total charge through a circuit depends on....
Current and time.
Electric current is a flow of....
Current is measured in....
Amperes ( A)
Charge is measured in...
Electric charge will only flow around a complete circuit if something is providing a potential difference. Give an example of a PD:
A battery - it is a 'driving force' that pushed charge around the circuit.
What is resistance?
Anything that slows down the flow of charge.
What does the size of a current tell you?
How fast the charge is flowing - this is known as the rate of flow charge.
Give the equation for finding the rate of CHARGE FLOW:
Charge flow = CURRENT X TIME
The current flowing through a component depends on: (2)
If there is a big resistance across a component, how does this affect the current that flows through?
The smaller the current.
Give the formulae for finding the potential difference:
CURRENT in amps X RESISTANCE in ohms
What are Ohmic Conductors?
Components with a fixed resistance. This means the resistance of the component doesn't change with current.
Ohmic Conductors only have a fixed resistance if .............. doesn't change.
Give 2 examples of Ohmic Conductors:
What is the link between the current and the potential difference in an Ohmic Conductor?
The current flowing through it is directly proportional to the potential difference across it. Meaning that of the potential difference doubles, so does the current.
Some components have a resistance that DOES change with the current. Explain how this works for a FILAMENT LAMP:
Filament lamps contain a wire which is designed to heat up and 'glow' as the current increases so as the current increases, the temperature of the filament increases too. Resistance increases with temperature so the resistance increases with current.
How does resistance work on DIODES?
The resistance depends on the direction of the current. It will let current flow in one direction but it has a very high resistance in the opposite direction which makes it hard for a current to flow that way.
The resistance of a circuit can depend on a number of things. Give 2 examples:
Give the 7 steps to investigating the effect of wire length in a circuit:
1) Attach a crocodile clip to the wire level with 0cm on the ruler.2) Attach the second crocodile clip to the wire a short distance from the first clip.3) Write down the length of the wire between the clips.4) Close the switch, record the current through the wire and the potential difference across it..5) Calculate the resistance of the wire using the equation.6) Open the switch and move the second crocodile clip along the wire.7) Repeat steps for a range of wire lengths.
How to plot a graph of your results AFTER INVESTIGATING THE EFFECT OF WIRE LENGTH IN A CIRCUIT: (4)
1) Plot a graph of resistance against wire length.2) Draw a line of best fit through your points.3) Your graph should be a straight line through the origin.4) This means resistance is directly proportional to length - the longer the wire, the greater the resistance.
What is "I-V Characteristics"?
A graph showing how the current flowing through the component changes as the potential difference across it changes.
What are components with STRAIGHT LINE IV Characteristics called? Give an example.
Linear Components. (e.g. a fixed resistor)
What are components with CURVED IV Characteristics called? Give an example.
Non-linear components (e.g.filament lamp or diode)
Give the 6 steps to investigating IV Characteristics on different components:
1) Set up a test circuit (the one on page 183 in revision guide)2) The variable resistor is used to change the current in the circuit. This changes the potential difference across the component.3) Set the resistance of the variable resistor and measure the current through and potential difference across the component.4) Swap over the current connected to the cell to reverse the direction of the current. The ammeter should now display negative readings.5) Repeat step 3 to get results for negative values of current.6) Plot a graph with current on the y axis and the potential difference on the x axis.
LDR is short for...
Light Dependant Resistor.
LDR - In bright light, is the resistance high or low?
LDR - In darkness, is the resistance high or low?
LDR's have lots of uses. Give 2.
What is a thermistor?
A temperature dependent resistor.
THERMISTORS - In hot conditions, does the resistance increase or decrease?
DROPS - decreases.
THERMISTORS - In cool conditions, does the resistance increase or decrease?
What do Thermistors do?
Turn the heating on when it's cool and off when it's warm. Can be used in car engines and for central heating.
What can sensing circuits be used for?
To automatically change the potential difference across components depending on changes in the environment.
What does a series circuit look like?
The components are all connected in a line between the ends of the power supply. Only voltmeters break this rule as they are always parallel.
What happens if you remove one component in a series circuit?
The circuit is broken so all the components stop working.
What is the potential difference like in series circuits?
The total potential difference of the supply is shared between all of the components - if you add the pd across each component you get the pd of the power supply. THE BIGGER THE RESISTANCE, THE BIGGER ITS SHARE OF THE TOTAL PD.
In a series circuit the same current flows through....
Give the equation to find the TOTAL RESISTANCE of a circuit:
Resistor TOTAL = resistance of 1 component + resistance of 2 component.
Give 5 points that explain WHY adding resistors in SERIES CIRCUITS increases the total resistance of the circuit:
What is a Parallel circuit like?
Each component is separately connected to the ends of the power supply. Only ammeters break this rule as they are always in series.
What happens if you take out one of the loops in a parallel circuit?
NOTHING. The things in the other loops won't be affected as they would in a series circuit.
What is the PD like in Parallel circuits?
All components get the full source PD so the potential difference is the same across all components.
In parallel circuits the total current in a circuit is equal to the....
Sum of all the currents through the separate components.
What happens AT JUNCTIONS in parallel circuits?
The current either splits or rejoins. The total current going into a junction must equal the total current leaving it.
Adding a resistor in PARALLEL reduces the total resistance. Give 4 points why:
1) if you had a resistor in parallel both a resistor still have the same potential difference across them as the power supply.2)This means the 'pushing force' for some making the current flow is still the same.3) but by adding another loop on the current has more than one direction to go in. 4) more current can flow around the circuit so the total current increases which means the total resistance of the circuit is lower.
INVESTIGATING CIRCUITSFIRST SET UP THE BASIC CIRCUITGive 5 steps to doing this.
1) Find at least 4 identical resistors.2) Build the circuit shown on the right PAGE 187 revision guide.3) Write down the PD of the battery. This is the pd of the circuit.4) Read the current in the circuit from the ammeter.5) Calculate the resistance.
INVESTIGATING CIRCUITSSTEP 2 ADDING RESISTORS IN SERIES Give the 3 steps
1) Add another resistor, in series with the first.2) Measure the current again and calculate resistance again. The pd is the same as the pd of the battery.3) Repeat steps 1 and 2 until you've added all of your resistors.
INVESTIGATING CIRCUITSSTEP 3 INVESTIGATING ADDING RESISTORS IN PARALLELGive the 5 steps.
1) Build the basic circuit again. you already know it's resistance.2) Use the same equipment so it's a fair test.3) Add another resistor, in parallel with the first.4) Measure the total current through the circuit and calculate the overall resistance of the circuit. The pd is still the same as before.5) repeat steps 3 and 4 until you've added all of your resistors.
INVESTIGATING CIRCUITSFINAL STEP DRAW GRAPHS TO COMPARE RESULTSWhat should results be?
SeriesAdding resistors in series increases the total resistance of the circuit.ParallelThe more resistors you add, the smaller the overall resistance becomes.Page 187 revision guide look at graphs.
What is the national grid?
A giant system of cables and transformers that covers the U.K. It transfers electrical power from power stations to consumers across the U.K.
Electricity production has to meet demand. Explain this.
Throughout the day, the amount of electricity used changes and the power stations have to produce enough electricity.
How does the national grid cope with high demand?
Power stations often run at well below their maximum power output so that they can increase their power if needed.
Why does the National Grid use a high PD and a low current?
To transmit a huge amount of power you either need a high potential difference or a high current. A high current means lots of energy is lost to thermal energy as wires are heated up so high PD is used to less energy is lost.
What are step up transformers?
Things used to increase the potential difference from power stations to electric cables.
What are Step DOWN transformers?
Things used to bring the potential difference back down to safe levels before the electricity gets to homes.
The energy transferred by a component depends on the potential difference across it and the charge flowing through it. Give the formulae for ENERGY TRANSFERRED:
CHARGE FLOW X POTENTIAL DIFFERENCE.
Power also depends on current and potential difference. Give the equation for the power of an appliance:
Potential difference x Current
Explain what the Live Wire does and what colour is it?
BROWNThe live wire provides the alternating potential difference from the mains supply - 230V.
Explain the Neutral Wire and what colour is it?
BlueCompletes the circuit. Usually the current flowed in through the live Wire and out through the neutral Wire. 0V.
Explain what the Earth Wire does and what colour is it?
Green and YellowA safety Wire, it stops the appliance becoming live: it is connected to the metal casing of an appliance. If a fault caused the live Wire to touch the casing, the current flows away through the earth Wire. 0V.
Explain how the live Wire (brown) can give you an electric shock.
There is a potential difference between the live Wire and your body. Touching it can cause a current to flow through your body because it has a pd of 230V. Our body is at 0V.
What is an ALTERNATING POTENTIAL DIFFERENCE?
A potential difference that is constantly changing direction. It produces an alternating current.
In an alternating current, the current is also constantly changing direction. Give an example of an Alternating current supply:
The UK Mains supply (electricity in your homes) is an ac supply at around 230V.
What is the frequency of the AC MAINS SUPPLY?
50Hz ( hertz)
What is direct current (dc)?
A current that is always flowing in the same direction. It is created by a direct potential difference.
When a charge moves around the circuit, work is done against the resistance of the circuit. Then what happens?
Whenever work is done, energy is transferred. When the work is done by a charge, the energy is transferred electrically. Electrical appliances transfer energy to components in the circuit when a current flows.
The total energy transferred by an appliance depends on : (2)
1) how long it's on for2) it's power (the energy that it transfers per second)
Give the equation that finds Energy Transferred:
Energy Transferred = POWER X TIME
Appliances often give a power rating. What's that?
The power that they work at. It tells you how much energy is transferred between stores when the appliance is used: an appliance with a higher power will cost more to run for a given time as it uses more energy.
The further an energy level is from the nucleus, the more...
Energy an election in that energy level has.
How can electrons move between energy levels? (2)
1) Absorbing electromagnetic radiation.2) Releasing electromagnetic radiation.
What happens if an electron in an outer energy level absorbs electromagnetic radiation?
It can leave the atom.
What happens if an atom loses one or more electrons?
It turns into a positively charged ion.
What is the number of protons in an atom called?
It's atomic number.
What gives the nucleus a positive charge?
The protons in the nucleus.
The mass number of an atom is the sum of...
The number of protons and the number of neutrons.
What is an element?
A substance only containing atoms with the same number of protons.
What are isotopes?
Atoms of an element with the same number of protons but different number of neutrons.
Isotopes of an element have the same…But a different...
Same = atomic number.Different = mass number.
What do isotopes do if they are unstable?What is this process called?
They emit (give out) radiation from their nuclei to try and become more stable.This process is called Radioactive Decay.
What is the radiation emitted from unstable isotopes called?
Name the four different types of nuclear radiation call
1) Alpha2) Beta3) Gamma4) Neutrons
An alpha particle is…
Two neutrons and two protons like a helium nucleus.
A Beta particle is...
A fast moving electron.
Gamma rays are...
Waves of electromagnetic radiation.
What is Ionising radiation?
A radiation that can knock electrons off atoms and turn them into ions.
What is the ionising power?
How easily a radiation can knock electrons off atoms and turn them into ions.
Alpha, beta and gamma rays are all types of....
ALPHA PARTICLES.What is their ionising power?
BETA PARTICLES.What is their ionising power?
GAMMA RAYS.What is their ionising power?
ALPHA PARTICLES.What is their range in air?
A few centimetres.
BETA PARTICLES.What is their range in air?
A few meters.
GAMMA RAYS.What is their range in air?
A long distance.
ALPHA PARTICLES.Stopped by...
A sheet of paper.
BETA PARTICLESStopped by...
A sheet of aluminium.
GAMMA RAYS.Stopped by...
Thick sheets of lead or metres or concrete.
Nuclear equations are a way of showing radioactive decay. How are they normally written?
Nucleus before decay ---> nucleus after decay + radiation emitted. The total mass and atomic numbers must be equal on both sides.
What is alpha decay?
When an alpha particle is emitted from a radioactive nucleus.
Does alpha decay increase or decrease the charge and mass of the nucleus?
What is Beta Decay?
When a beta particle is emitted from a radioactive nucleus.
During a beta decay, what is a neutron in the nucleus turned into?
Does Beta Decay increase or decrease the charge of the nucleus?
Do Gamma rays change the charge or mass of the nucleus?
No because they are a way of getting rid of extra energy from the nucleus.
The radiation given out by a radioactive decay can be measured with: (2)
1) A Geiger Muller tube.2) Counter Detector.
The number of decays the counter measures every second is called the...
What is the activity of a radioactive source?
The rate at which it decays - this means how many unstable nuclei decay every second.
What is activity measured in?
Becquerels. BQ. 1 BQ is 1 Decay per second.
Radioactive decay is entirely random. What does this mean you can't do?
You can't predict exactly which nucleus in a sample will decay next or when any of them will decay.
Since you can't predict exactly when radioactivity happens, what can you do instead?
You can predict how long it will take for half of the nuclei to decay. This is known as half life.
What is half life?
The time taken for the number of nuclei of a radioactive isotope in a sample to halve.
Half life is also...
The time taken for the count rate or activity of a sample to fall to half of its initial value.
The half life of a radioactive sample will always be the...
Same. This meant it doesn't matter what activity you start with when doing half life calculations.
How do you calculate half lives?
You just need to know how long it takes for the activity or count rate of the source to halve.
How can Ionising Radiation be bad?
They can enter living cells and ionise atoms in them which causes damage to the cell. This may cause cancer or kill cells of completely.
Exposure to radiation is called...
Objects near a radioactive source can be irradiated by it. What does this mean?
Radiation from the radioactive source will reach the object.
The further you are from a particular source, the less...
Radiation will reach you.
To help stop irradiation happening, you should: (3)
1) Store radioactive sources in lead lined boxes when they're not being used.2) Stand behind barriers that will absorb radiation when using sources.3) Keep the source as far away from you as possible e.g. Hold it at arm's length.
What is contamination?
When unwanted radioactive atoms get into or onto an object.
What do contaminating atoms do?
They might then decay and release radiation which could harm you.
Being contaminated by a source may cause more damage than if you are irradiated by the same source. Why?
Because you may carry it for a long time.
To help stop contamination, you should...
Wear gloves and use tongs when handling radioactive sources.
What are the most dangerous sources to be irradiated by?
Beta and Gamma.
Why are Beta and Gamma the most dangerous sources to be irradiated by? (2)
1) they have long ranges which means more radiation will reach you from a beta or gamma source than from an alpha source at the same distance.2) they can penetrate through your body and may damage your organs. Alpha isn't as dangerous as it can't get through skin and is easily blocked.
What is the most dangerous source to be contaminated by INSIDE the body?
Alpha because they are the most ionising type of radiation. Beta and Gamma are less damaging because they are less ionising.
What source is the least dangerous inside the body and why?
Gamma sources because gamma rays are the least ionising type of radiation and they mostly pass straight out without any damage.