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AQA GCSE PHYSICS (9-1)
Topic 1: Energy
4.1.1 Energy changes in a system, and the ways energy is stored before and after such changes
4.1.1.1 Energy stores and systems
A system is an object or group of objects.
There are changes in the way energy is stored when a system changes.
For example:
an object projected upwards a moving object hitting an obstacle an object accelerated by a constant force a vehicle slowing down bringing water to a boil in an electric kettle.
Students should be able to:
Describe all the changes involved in the way energy is stored when a system changes, for common situations (including the examples above).
Throughout this Energy topic, calculate the changes in energy involved when a system is changed by: heating, work done by forces, work done when a current flows.
Use calculations to show on a common scale how the overall energy in a system is redistributed when the system is changed.
4.1.1.2 Changes in energy
The kinetic energy of a moving object can be calculated using the equation:
kinetic energy, E k , in joules, J mass, m , in kilograms, kg speed, v , in metres per second, m/s
The amount of elastic potential energ y stored in a stretched spring can be calculated using the equation:
(assuming the limit of proportionality has not been exceeded)
elastic potential energy, E e, in joules, J spring constant, k , in newtons per metre, N/m extension, e , in metres, m
The amount of gravitational potential energy gained by an object raised above ground level can be calculated using the equation:
gravitational potential energy, E p, in joules, J mass, m , in kilograms, kg gravitational field strength, g , in newtons per kilogram, N/kg ( In any calculation the value of the gravitational field strength (g) will be given ) height, h , in metres, m
Students should be able to:
Calculate the amount of energy associated with a moving object , a stretched spring and an object raised above ground level.
Recall and apply the equation for kinetic energy
Apply the equation for elastic potential energy , which is given on the Physics equation sheet
Recall and apply the equation for gravitational potential energy
4.1.1.3 Energy changes in systems
The amount of energy stored in or released from a system as its temperature changes can be calculated using the equation:
change in thermal energy, ∆ E , in joules, J mass, m , in kilograms, kg specific heat capacity, c , in joules per kilogram per degree Celsius, J/kg °C temperature change, ∆θ, in degrees Celsius, °C
The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
Students should be expected to:
Apply the equation for specific heat capacity , which is given on the Physics equation sheet.
REQUIRED PRACTICAL : Specific Heat Capacity. AT 1 and 5.
4.1.1.4 Power
Power is defined as the rate at which energy is transferred or the rate at which work is done.
power, P , in watts, W energy transferred, E , in joules, J work done, W , in joules, J time, t , in seconds, s
An energy transfer of 1 joule per second is equal to a power of 1 watt.
Students should be able to:
Recall and apply both of the equations for power.
Give examples that illustrate the definition of power e.g. comparing two electric motors that both lift the same weight through the same height but one does it faster than the other.
4.1.2 Conservation and dissipation of energy
4.1.2.1 Energy transfers in a system
Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.
Whenever there are energy transfers in a system only part of the energy is usefully transferred.
The rest of the energy is dissipated so that it is stored in less useful ways. This energy is often described as being ‘ wasted ’.
Unwanted energy transfers can be reduced in a number of ways, for example through lubrication and the use of thermal insulation.
Topic 2: Electricity
4.2.1 Current, potential difference and resistance
4.2.1.1 Standard circuit diagram symbols
Circuit diagrams use standard symbols.
Students should be able to:
Draw and interpret circuit diagrams.
Recall all the circuit symbols shown above
4.2.1.2 Electrical charge and current
For electrical charge to flow through a closed circuit the circuit must include a source of potential difference.
Electric current is a flow of electrical charge. The size of the electric current is the rate of flow of electrical charge.
Charge flow, current and time are linked by the equation:
charge flow, Q , in coulombs, C current, I , in amperes, A (amp is acceptable for ampere) time, t , in seconds, s
The current at any point in a single closed loop of a circuit has the same value as the current at any other point in the same closed loop.
Students should be able to:
Recall and apply the equation for current stated above.
4.2.1.3 Current, resistance and potential difference
The current ( I ) through a component depends on both the resistance ( R )of the component and the potential difference ( V ) across the component.
The greater the resistance of the component the smaller the current for a given potential difference (p.d.) across the component.
Current, potential difference or resistance can be calculated using the equation:
potential difference, V , in volts, V current, I , in amperes, A (amp is acceptable for ampere) resistance, R , in ohms, Ω
Students should be able to:
Recall and apply the equation linking current , potential difference and resistance.
Recognise that potential difference refers to voltage.
REQUIRED PRACTICAL – Resistance. AT 1, 6 and 7.
4.2.1.4 Resistors
The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. This means that the resistance remains constant as the current changes.
The resistance of components such as lamps , diodes , thermistors and LDRs is not constant; it changes with the current through the component.
The resistance of a filament lamp increases as the temperature of the filament increases.
The current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction.
The resistance of a thermistor decreases as the temperature increases.
The applications of thermistors in circuits e.g. a thermostat is required.
The resistance of an LDR decreases as light intensity increases.
The application of LDRs in circuits e.g. switching lights on when it gets dark is required.
Students should be able to:
Explain that, for some resistors, the value R remains constant but that in others it can change as the current changes.
Explain the design and use of a circuit to measure the resistance of a component by measuring the current through, and potential difference across, the component.
Draw an appropriate circuit diagram using correct circuit symbols.
Use graphs to determine whether circuit components are linear or non-linear and relate the curves produced to the function and properties of the component.
MS 4c Plot two variables from experimental or other data.
The potential difference between the live wire and earth (0 V) is about 230 V.
The neutral wire is at, or close to, earth potential (0 V).
The earth wire is at 0 V, it only carries a current if there is a fault.
Our bodies are at earth potential (0 V). Touching the live wire produces a large potential difference across our body. This causes a current to flow through our body, resulting in an electric shock.
Students should be able to:
Explain that a live wire may be dangerous even when a switch in the mains circuit is open.
Explain the dangers of providing any connection between the live wire and earth.
4.2.4 Energy transfers
4.2.4.1 Power
The power of a device is related to the potential difference across it and the current through it by the equation:
power, P , in watts, W potential difference, V , in volts, V current, I , in amperes, A (amp is acceptable for ampere) resistance, R , in ohms, Ω
Students should be able to:
Recall and apply both equations for power.
Explain how the power transfer in any circuit device is related to the potential difference across it and the current through it, and the energy changes over time.
4.2.4.2 Energy transfers in everyday appliances
Everyday electrical appliances are designed to bring about energy transfers.
The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance.
The amount of energy transferred by electrical work can be calculated using the equation:
energy transferred, E , in joules, J power, P , in watts, W time, t , in seconds, s
Work is done when charge flows in a circuit.
energy transferred, E , in joules, J charge flow, Q , in coulombs, C potential difference, V , in volts, V
Students should be able to:
Recall and apply both equations for energy transfer.
Describe how different domestic appliances transfer energy from batteries or a.c. mains to the kinetic energy of electric motors or the energy of heating devices.
Explain how the power of a circuit device is related to: the p.d. across it and the current through it. the energy transferred over a given time.
Describe , with examples, the relationship between the power ratings for domestic electrical appliances and the changes in stored energy when they are in use.
4.2.4.3 The National Grid
The National Grid is a system of cables and transformers linking power stations to consumers.
Electrical power is transferred from power stations to consumers using the National Grid.
Step-up transformers are used to increase the potential difference from the power station to the transmission cables then step-down transformers are used to decrease , to a much lower value, the potential difference for domestic use.
This is done because, for a given power, increasing the potential difference reduces the current , and hence reduces the energy losses due to heating in the transmission cables.
Students should be able to:
Explain why the National Grid system is an efficient way to transfer energy.
4.2.5 Static electricity – GCSE PHYSICS ONLY.
4.2.5.1 Static charge
When certain insulating materials are rubbed against each other they become electrically charged.
Negatively charged electrons are rubbed off one material and on to the other. The material that gains electrons becomes negatively charged. The material that loses electrons is left with an equal positive charge.
The greater the charge on an isolated object the greater the potential difference between the object and earth. If the potential difference becomes high enough a spark may jump across the gap between the object and any earthed conductor which is brought near it.
When two electrically charged objects are brought close together they exert a force on each other. Two objects that carry the same type of charge repel. Two objects that carry different types of charge attract. Attraction and repulsion between two charged objects are examples of non-contact force.
Students should be able to:
Describe the production of static electricity, and sparking, by rubbing surfaces.
Describe evidence that charged objects exert forces of attraction or repulsion on one another when not in contact.
Explain how the transfer of electrons between objects can explain the phenomena of static electricity.
4.2.5.2 Electric fields
A charged object creates an electric field around itself. The electric field is strongest close to the charged object. The further away from the charged object, the weaker the field.
A second charged object placed in the field experiences a force. The force gets stronger as the distance between the objects decreases.
Students should be able to:
Draw the electric field pattern for an isolated charged sphere.
Explain the concept of an electric field.
Explain how the concept of an electric field helps to explain the non-contact force between charged objects as well as other electrostatic phenomena such as sparking.
The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
Students should be able to:
Apply the equation for specific heat capacity which is given on the Physics equation sheet.
4.3.2.3 Changes of heat and specific latent heat
If a change of state happens:
The energy needed for a substance to change state is called latent heat. When a change of state occurs, the energy supplied changes the energy stored ( internal energy ) but not the temperature.
The specific latent heat of a substance is the amount of energy required to change the state of one kilogram of the substance with no change in temperature.
The following equation applies:
energy, E , in joules, J mass, m , in kilograms, kg specific latent heat, L , in joules per kilogram, J/kg
Specific latent heat of fusion – change of state from solid to liquid
Specific latent heat of vaporisation – change of state from liquid to vapour
Students should be able to:
Interpret heating and cooling graphs that include changes of state.
Distinguish between specific heat capacity and specific latent heat.
Apply the equation for specific latent heat which is given on the Physics equation sheet.
4.3.3 Particle model and pressure
4.3.3.1 Particle motion in gases
The molecules of a gas are in constant random motion.
The temperature of the gas is related to the average kinetic energy of the molecules. The higher the temperature the greater the average kinetic energy and so the faster the average speed of the molecules.
When the molecules collide with the wall of their container they exert a force on the wall. The total force exerted by all of the molecules inside the container on a unit area of the walls is the gas pressure.
Changing the temperature of a gas, held at constant volume, changes the pressure exerted by the gas.
Students should be able to:
Explain how the motion of the molecules in a gas is related to both its temperature and its pressure.
Explain qualitatively the relationship between temperature of a gas and its pressure at constant volume.
4.3.3.2 Pressure in gases (GCSE Physics only)
A gas can be compressed or expanded by pressure changes. The pressure produces a net force at right angles to the wall of the gas container (or any surface).
For a fixed mass of gas held at a constant temperature:
pressure, p , in pascals, Pa volume, V , in metres cubed, m^3
Students should be able to:
Use the particle model to explain how increasing the volume in which a gas is contained, at constant temperature, can lead to a decrease in pressure.
Apply the pressure equation above which is given on the Physics equation sheet.
Calculate the change in the pressure of a gas or the volume of a gas (a fixed mass held at constant temperature) when either the pressure or volume is increased or decreased.
4.3.3.3 Increasing the pressure of a gas (GCSE Physics only) (HT only)
Work is the transfer of energy by a force.
Doing work on a gas increases the internal energy of the gas and can cause an increase in the temperature of the gas.
Students should be able to:
Explain how, in a given situation e.g. a bicycle pump, doing work on an enclosed gas leads to an increase in the temperature of the gas.
Topic 4: Atomic Structure
4.4.1 Atoms and isotopes
4.4.1.1 The structure of an atom
Atoms are very small, having a radius of about 1 × 10-10^ metres.
The basic structure of an atom is a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons.
The radius of a nucleus is less than 1/10 000 of the radius of an atom. Most of the mass of an atom is concentrated in the nucleus.
The electrons are arranged at different distances from the nucleus (different energy levels ). The electron arrangements may change with the absorption of electromagnetic radiation (move further from the nucleus; a higher energy level) or by the emission of electromagnetic radiation (move closer to the nucleus; a lower energy level).
Students should be able to:
Recognise expressions given in standard form.
4.4.1.2 Mass number, atomic number and isotopes
In an atom the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
All atoms of a particular element have the same number of protons. The number of protons in an atom of an element is called its atomic number.
The total number of protons and neutrons in an atom is called its mass number.
Atoms can be represented as shown in this example:
Atoms of the same element can have different numbers of neutrons ; these atoms are called isotopes of that element.
Atoms turn into positive ions if they lose one or more outer electron (s).
Gamma rays travel great distances through the air and pass through most materials but are
absorbed by a thick sheet of lead or several metres of concrete. Gamma rays are weakly
ionising.
Students should be able to:
Apply their knowledge to the uses of radiation and evaluate the best sources of radiation to use in a given situation.
Required knowledge of the properties of alpha particles, beta particles and gamma rays is limited to their penetration through materials, their range in air and ionising power.
4.4.2.2 Nuclear equations
Nuclear equations are used to represent radioactive decay.
In a nuclear equation an alpha particle may be represented by the symbol:
And a beta particle by the symbol:
The emission of the different types of nuclear radiation may cause a change in the mass and /or the charge of the nucleus. For example:
So alpha decay causes both the mass and charge of the nucleus to decrease.
So beta decay does not cause the mass of the nucleus to change but does cause the charge of the nucleus to increase. Students are not required to recall these two examples.
The emission of a gamma ray does not cause the mass or the charge of the nucleus to change.
Students should be able to:
Use the names and symbols of common nuclei and particles to write balanced equations that show single alpha (α) and beta (β) decay. This is limited to balancing the atomic numbers and mass numbers. The identification of daughter elements from such decays is not required.
4.4.2.3 Half-lives and the random nature of radioactive decay
Radioactive decay is random. It is not possible to predict which individual nucleus will decay next. But, with a large enough number of nuclei, it is possible to predict how many will decay in a certain amount of time.
The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve , or the time it takes for the count rate (or activity) from a sample containing the
isotope to fall to half its initial level.
Students should be able to:
Explain the concept of half-life and how it is related to the random nature of radioactive decay.
Determine the half-life of a radioactive isotope from given information.
(HT only) Calculate the net decline, expressed as a ratio , in a radioactive emission after a given number of half-lives.
4.4.2.4 Radioactive contamination
Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials.
The hazard from contamination is due to the decay of the contaminating atoms. The type of radiation emitted affects the level of hazard.
Irradiation is the process of exposing an object to nuclear radiation. The irradiated object does not become radioactive.
Suitable precautions must be taken to protect against any hazard that the radioactive source used in the process of irradiation may present.
Students should be able to:
Compare the hazards associated with contamination and irradiation.
Understand that it is important for the findings of studies into the effects of radiation on humans to be published and shared with other scientists so that the findings can be checked by peer review.
4.4.3 Hazards and uses of radioactive emissions and of background radiation (GCSE Physics only)
4.4.3.1 Background radiation
Background radiation is around us all of the time. It comes from:
natural sources such as rocks and cosmic rays from space man-made sources such as the fallout from nuclear weapons testing and nuclear accidents.
The level of background radiation and radiation dose may be affected by occupation and/or location.
Radiation dose is measured in sieverts (Sv). 1000 millisieverts (mSv) = 1 sievert (Sv).
Students will not need to recall the unit of radiation dose.
4.4.3.2 Different half-lives of radioactive isotopes
Radioactive isotopes have a very wide range of half-life values.
Sources containing nuclei that are most unstable have the shortest half-lives. The decay is rapid with a lot of radiation emitted in a short time. Sources with nuclei that are least unstable have the longest half-lives. These sources emit little radiation each second but emit radiation for a long time.
Students should be able to:
Explain why the hazards associated with radioactive material differ according to the half-life involved.
Use data presented in standard form.
4.4.3.3 Uses of nuclear radiation
Nuclear radiations are used in medicine for the:
exploration of internal organs control or destruction of unwanted tissue.
Students should be able to:
Describe and evaluate the uses of nuclear radiations for exploration of internal organs, and for control or destruction of unwanted tissue.
Evaluate the perceived risks of using nuclear radiations in relation to given data and consequences.
4.4.4 Nuclear fission and fusion (GCSE Physics only)
4.4.4.1 Nuclear fission
Nuclear fission is the splitting of a large and unstable nucleus (e.g. uranium or plutonium).
Spontaneous fission is rare. Usually, for fission to occur the unstable nucleus must first absorb a neutron.
The nucleus undergoing fission splits into two smaller nuclei, roughly equal in size, and emits two or three neutrons plus gamma rays. Energy is released by the fission reaction.
