Physics (8463)- Paper 1

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 being projected upwards
• a moving object hitting an obstacle
• an object being accelerated by a constant force
• a vehicle slowing down
• bringing water to boil in an electrical kettle

Some changes involved in the way energy is stored when a system is changed: 

• vehicle braking systems (such as bike brakes)
• a ball being thrown upwards

You can calculate the changes in energy involved when a system is changed by:

• heating
• work done by forces
• work done when charge flows

Kinetic Energy = 0.5 x mass x (speed)2
kinetic energy, E_k, in joules, J; mass, m, in kilograms, kg; speed, v, in metres per second, m/s

Elastic potential energy = 0.5 × spring constant × (extension)²
elastic potential energy, E_e, in joules, J; spring constant, k, in newtons per metre, N/m; extension,
e, in metres, m

G . P . E . = mass × gravitational field strength × height
gravitational potential energy, E_p, in joules, J; mass, m, in kilograms, kg;
gravitational field strength, g, in newtons per kilogram, N/kg; height, h, in metres, m

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 = mass × specific heat capacity × temperature change,  ΔE = m c Δθ

• change in thermal energy, ΔE, in joules, J; mass, m, in kilograms, kg;
• specific heat capacity, c, in joules per kilogram per degree Celsius, J/kg °C
• temperature change, Δθ, 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.

Power is defined as the rate at which energy is transferred or the rate at which work is done.

power = energy transferred / time,  P = E / t

power = work done / time,    P = W / t

power, P, in watts, W; energy transferred, E, in joules, J;
time, t, in seconds, s; work done, W, in joules, J

An energy transfer of 1 joule per second is equal to a power of 1 watt.

Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.
Most Kids Hate Learning GCSE Energy Names

M= Magnetic
K= Kinetic
H= Heat
L= Light
G= Gravitational 
C= Chemical
S= Sound
E= Electric 
E= Elastic 
N= Nuclear

Different types of energy can be transferred from one type to another. Energy transfer diagrams show each type of energy, whether it is stored or not, and the processes taking place as it is transferred. Sankey diagrams also show the relative amounts of each type of energy and how much energy is wasted. 

The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.

Energy efficiency for any energy transfer can be calculated using the equation:
efficiency = useful output energy transfer / total input energy transfer

Efficiency may also be calculated using the equation:
efficiency = useful power output / total power input

Te main energy resources available for use on Earth include: fossil fuels (coal, oil and gas), nuclear fuel, bio-fuel, wind, hydroelectricity, geothermal, the tides, the Sun and water waves. A renewable energy resource is one that is being (or can be) replenished as it is used. The uses of energy resources include: transport, electricity generation and heating. Fossil, Nuclear, Renewables and Electric are the main energy sources.
Renewable: Solar, wind, hydro, bio, geothermal
Non-Renewable: Nuclear, coal, oil, natural gas

Can you compare some ways that different energy resources are used: the uses to include transport, electricity generation and heating?

The issue of waste products. Notoriously, fossil fuels impact the environment negatively with pollution (air, water, environment, and frequently noise). More geo-friendly fuels (solar, wind, geothermal) have the benefit of almost no adverse effects to the environment. The advantage of oil is that you just pull it out of the ground for essentially free. It's easy to move around, store, and use as a fuel source. Other major fuel sources (like natural gas, coal, wood) are like that as well - the raw materials are lying around us for the gathering. 

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 = current × time,    Q = I t

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.

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 (pd) across the component. Questions will be set using the term potential difference. You will gain credit for the correct use of either potential difference or voltage. Current, potential difference or resistance can be calculated using the equation:

potential difference = current × resistance,   V = I R

potential difference, V, in volts, V;

current, I, in amperes, A (amp is acceptable for ampere)

resistance, R, in ohms, Ω

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 eg a thermostat is required. The resistance of an LDR decreases as light intensity increases. The application of LDRs in circuits eg switching lights on when it gets dark is required.

There are two ways of joining electrical components, in series and in parallel. Some circuits include both series and parallel parts.For components connected in series:

• there is the same current through each component
• the total potential difference of the power supply is shared between the components
• the total resistance of two components is the sum of the resistance of each component.

Rtotal = R1 + R2 resistance,

R, in ohms, Ω

For components connected in parallel:

• the potential difference across each component is the same
• the total current through the whole circuit is the sum of the currents through the separate components
• the total resistance of two resistors is less than the resistance of the smallest individual resistor.

Mains electricity is an a.c. supply. In the United Kingdom it has a frequency of 50 Hz and is about 230 V.

In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction.

Most electrical appliances are connected to the mains using three-core cable. The insulation covering each wire is colour coded for easy identification: live wire – brown neutral wire – blue earth wire – green and yellow stripes. The live wire carries the alternating potential difference from the supply. The neutral wire completes the circuit. The earth wire is a safety wire to stop the appliance becoming live. 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.A live wire may be dangerous even when a switch in the mains circuit is open. If a fault occurs where the live wire connects to the case, the earth wire allows a large current to flow through the live and earth wires. This overheats the fuse which melts and breaks the circuit.

The power of a device is related to the potential difference across it and the current through it by the equation:

power = potential difference × current,    P = V I,  

power = (current)2 × resistance,   P = I2 R

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

The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance. Different domestic appliances transfer energy from batteries or a.c. mains to the kinetic energy of electric motors or the energy of heating devices.

Work is done when charge flows in a circuit. The amount of energy transferred by electrical work can be calculated using the equation:

energy transferred = power × time,    E = P t

energy transferred = charge flow × potential difference,    E = Q V

energy transferred, E, in joules, J;
power, P, in watts, W;
time, t, in seconds, s
charge flow, Q, in coulombs, C;
potential difference, V, in volts

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.

National Grid system is an efficient way to transfer energy because it reduces energy loss during transmission.

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.

The particle model is widely used to predict the behaviour of solids, liquids and gases and this has many applications in everyday life. It helps us to explain a wide range of observations and engineers use these principles when designing vessels to withstand high pressures and temperatures such as submarines and spacecraft. It also explains why it is difficult to make a good cup of tea high up a mountain!

The density of a material is defined by the equation:

density = mass / volume,    ρ = m / V

density, ρ, in kilograms per metre cubed, kg/m3;
mass, m, in kilograms, kg;
volume, V, in metres cubed, m3

The particle model can be used to explain:

• the different states of matter
• differences in density

When substances change state (melt, freeze, boil, evaporate, condense or sublimate), mass is conserved. Changes of state are physical changes: the change does not produce a new substance. If the change is reversed the substance recovers its original properties. You should understand why there is no change in the mass of a substance when it changes state.

Energy is stored inside a system by the particles (atoms and molecules) that make up the system. This is called internal energy. Internal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system. Heating changes the energy stored within the system by increasing the energy of the particles that make up the system. This either raises the temperature of the system or produces a change of state.

The temperature of the system increases: The increase in temperature depends on the mass of the substance heated, the type of material and the energy input to the system.
The following equation applies:

change in thermal energy = mass × specific heat capacity × temperature change,   Δ E = m c Δθ

change in thermal energy, ΔE, in joules, J;
mass, m, in kilograms, kg
specific heat capacity, c, in joules per kilogram per degree Celsius, J/kg °C;
temperature change, Δθ, 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.

Know that 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.

energy for a change of state = mass × specific latent heat,    E = m L

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

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.

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 × volume = constant,     p V = constant

pressure, p, in pascals, Pa;
volume, V, in metres cubed, m3;

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.

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 to a higher energy level) of by the emission of electromagnetic radiation (move closer to the nucleus to a lower energy level).

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 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 electrons.

Atoms turn into negative ions if they gain one or more outer electrons.

New experimental evidence may lead to a scientific model being changed or replaced. 
Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided. The discovery of the electron led to the plum pudding model of the atom. The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it. 
The results of Rutherford and Marsden’s alpha scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. Rutherford and Marsden’s alpha scattering experiment led to the plum pudding model being replaced by the nuclear model.
Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances. The theoretical calculations of Bohr agreed with experimental observations. Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name proton was given to these particles.The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an accepted scientific idea.

Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable. This is a random process called radioactive decay. Activity is the rate at which a source of unstable nuclei decay. Activity is measured in becquerel (Bq), 1 becquerel = 1 decay per second. Count-rate is the number of decays recorded each second by a detector (eg Geiger-Muller tube). 1 becquerel = 1 count per second

The nuclear radiation emitted may be:

• an alpha particle (α) – this consists of two neutrons and two protons, it is the same as a helium nucleus
• a beta particle (β) – a high speed electron ejected from the nucleus as a neutron turns into a proton
• a gamma ray (γ) – electromagnetic radiation from the nucleus
• a neutron (n).

The properties of alpha particles, beta particles and gamma rays you need to know are their penetration through materials, their range in air and ionising power.

Alpha particles have a range in air of just a few centimetres and are absorbed by a thin sheet of paper. Alpha particles are strongly ionising.

Beta particles have a range in air of a few metres and are completely absorbed by a sheet of aluminium about 5 mm thick. Beta particles are moderately ionising.

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.

The nucleus of an atom can be represented as:
Shows X representing the chemical symbol. In front of X, A (at the top) represents atomic mass and Z (at the bottom) represents atomic number
In this symbol:

• A is the atomic mass (number of protons + neutrons)
• Z is the atomic number (number of protons)
• X is chemical symbol (as shown on the Periodic Table)

Two protons and two neutrons are lost from a nucleus when it emits an alpha particle. This means that:

• The atomic mass number decreases by 4.
• The atomic number decreases by 2.

A new element is formed that is two places lower in the Periodic Table than the original element.

In beta decay, a neutron changes into a proton plus an electron. The proton stays in the nucleus. The electron leaves the atom with high energy as a beta particle.

The nucleus has one more proton and one less neutron when it emits a beta particle. This means that:

• The atomic mass number stays the same
• The atomic number increases by 1

Radioactive decay is random so 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 average time it takes for the number of nuclei of the isotope in a sample to halve, or the average time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.

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 the radioactive source used in the process of irradiation may present.

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) and 1000 millisieverts (mSv) = 1 sievert (Sv)

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.

Nuclear radiations are used in medicine for the:

• exploration of internal organs
• control or destruction of unwanted tissue.

You 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.

Nuclear fission is the splitting of a large and unstable nucleus (eg 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. All of the fission products have kinetic energy. The neutrons may go on to start a chain reaction. The chain reaction is controlled in a nuclear reactor to control the energy released.

The explosion caused by a nuclear weapon is caused by an uncontrolled chain reaction.

Nuclear fusion is the joining of two light nuclei to form a heavier nucleus. In this process some of the mass of the smaller nuclei is converted into energy.

Some of this energy may be the energy of emitted radiation. Because all nuclei have positive charge, very high temperatures and pressures are needed to bring them close enough for fusion to happen.