Properties of Waves

• Waves may be either transverse or longitudinal
• A wave transfers information or energy
• Waves can cause matter to oscillate but matter itself is not transferred, only energy
• In transverse waves, oscillations are perpendicular to the direction of energy transfer
• Water waves and light waves are examples of transverse waves
• In longitudinal waves, oscillations are parallel to the direction of energy transfer
• Sound waves are an example of longitudinal waves
• Longitudinal waves show areas of compression and rarefaction
• Waves can be reflected or refracted
• Wave frequency is the number of waves that pass a point per second
• The unit of frequency is Hertz (Hz)
• The (time) period is the length of time it takes one wave to pass a given point
• The frequency of a wave can be calculated using the equation: frequency (Hz) = 1/time period (s)
• The wavelength of a wave is the distance from a point on one wave to the identical point on the next wave, measured in metres
• The amplitude of the wave is the maximum distance of a point on the wave from its rest position
• The peak of a wave is the maximum (highest) point of a wave
• The trough of a wave is the minimum (lowest) point of a wave
• Increasing the amplitude increases the volume of a sound wave
• Increasing the frequency increases the pitch of a sound wave
• The velocity of a wave is the speed of the wave in the direction it is travelling
• The velocity of a wave can be calculated using the equation:
   Velocity(m/s)=Displacement (m)Time (s) 
• This equation can be represented as: v = d/t
• The velocity of a wave can be calculated using the equation:
   Velocity (m/s)=Frequency Hz x Wavelength m
• This equation can be represented as: v = f x λ
• The velocity of a wave on a string can be calculated by recording the frequency of a signal generator and measuring across as many wavelengths as possible and dividing by the number of waves. These values can then be used in the equation v = f x λ
• The velocity of a wave in a ripple tank can be calculated by measuring across as many wavelengths as possible and dividing by the number of waves and counting the number of waves passing a point in 20 seconds and dividing by 20 to get the frequency. These values can then be used in the equation v = f x λ
  
  Sound and Ultrasound
• Sound is an example of a longitudinal wave
• Sound is made when an object causes air particles to vibrate
• Sound waves can travel through solids causing vibrations in the solid
• Increasing the amplitude causes a louder sound
• Increasing the frequency causes a higher pitch sound
• Humans can hear a range of 20-20000 Hz. Ultrasound has a frequency higher than 20000 Hz
• Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound. The conversion of sound waves to vibrations of solids works over a limited frequency range. This restricts the limits of human hearing
• Humans can hear a range of frequencies from 20 Hz to 20000 Hz
• Ultrasound waves have a frequency higher than the upper limit of hearing for humans. Ultrasound waves are partially reflected when they meet a boundary between two different media. The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is. This allows ultrasound waves to be used for both medical and industrial imaging
• Echo sounding, using high frequency sound waves is used to detect objects in deep water and measure water depth

Reflection and Refraction

• Waves can be reflected, absorbed or transmitted at the boundary between two different materials
• A medium is anything through which waves can move (or be transmitted). Examples include water, air and glass
• When light reaches a different medium, some light can be reflected and some is refracted
• Light waves can be represented by ray diagrams
• The incident ray is the incoming ray
• The normal line is an imaginary line from which angles are measured. It is drawn right angles to the surface of the medium
• The angle of incidence is the angle between the normal and the incidence ray

The reflected ray is the outgoing ray

• The angle of reflection is the angle between the normal and the reflected ray
• The Law of Reflection states that the angle of incidence is equal to the angle of reflection
• All objects reflect some light. A clear image can be seen with a mirror or a smooth shiny surface
• Rough objects scatter light where light rays bounce off in all directions
• Refraction occurs when light enters a material of different density
• Refraction happens because the change in speed of light causes it to change direction
• When light moves from a more dense medium to a less dense medium it speeds up and bends away from the normal
• When light moves from a less dense medium to a more dense medium it slows down and bends towards the normal
• During refraction the velocity and the wavelength of the wave change but the frequency remains the same
• Refracted ray is the outgoing ray
• The angle of refraction is the angle between the normal and the refracted ray
• Light bends towards the normal when it enters a denser medium and slows down
• Light bends away from the normal when it enters a less dense medium and speeds up
•  

Technological Uses of Waves

• The differences in velocity, absorption and reflection between different types of wave in solids and liquids can be used both for detection and exploration of structures which are hidden from direct observation, such as the structure of the Earth
• Seismic waves are produced by earthquakes
• P-waves are longitudinal, seismic waves
• P-waves travel at different speeds through solids and liquids
• S-waves are transverse, seismic waves
• S-waves cannot travel through a liquid
• P-waves and S-waves provide evidence for the structure and size of the Earth’s core

Disciplinary Knowledge

• Relate derived quantities with the formulae to calculate those quantities
• Visualise and represent 2D and 3D forms including 2 dimensional representations of 3D objects
• Know the difference between a scientific question and a non-scientific question (a question that science can answer)
• Define and understand the term hypothesis

Practical Skills

• Draw ray diagrams to represent reflection and refraction
• Measure motion, including determination of speed and rate of change of speed (acceleration/deceleration)
• Making observations of waves in fluids and solids to identify the suitability of apparatus to measure speed, frequency and wavelength. Making observations of the effects of the interaction of electromagnetic waves with matter

Mains Electricity

• Mains electricity is an a.c. supply.
• In alternating current (a.c.) the movement of charge changes direction
• Direct current (d.c.) is the movement of charge in one direction only
• Cells and batteries supply direct current (d.c.)
• In the United Kingdom the domestic electricity supply has a frequency of 50 Hz and is about 230 V
• A switch or a fuse in an electrical circuit is always connected to the live wire so that the socket or appliance is not live when switched off
• If the switch or fuse is placed in the neutral wire, the electrical appliance is still connected to the high voltage live wire even when the switch is open, or the fuse is blown
• This could cause the user to get an electric shock if they touched the inside of the appliance
• Most electrical appliances are connected to the mains using a 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 230 V alternating potential difference from the power supply to the appliance
• The neutral wire completes the circuit from the appliance back to the power supply
• The earth wire is a safety wire to stop the appliance becoming live by providing a path for a fault current to flow to earth. It also causes the protective device (either a circuit-breaker or fuse) to switch off the electric current to the circuit that has the fault
• The earth wire is not required to complete the circuit
• 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.
• Some countries do not routinely include the earth wire as a safety feature in their plugs. This results in a 2-pin plug
• A fuse is a safety device that prevents a high current from flowing through the circuit
• A high current could damage the appliances and wiring
• A fuse is made of a substance with a very low melting point. When a high current flows through, this substance melts, breaking the circuit.
• A circuit breaker works in the same way as a fuse, except it can be reset with a switch

Power in 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
• Different domestic appliances transfer energy from batteries or ac mains to the kinetic energy of electric motors or the energy of heating devices
• Power is the amount of energy transferred per unit time (rate at which energy is transferred), or the rate at which work is done
• The amount of energy transferred by electrical work can be calculated using the equation: Energy Transferred J=Power W x Time s
• This equation can be represented as: E = P x t
• Energy transferred, E, is measured in joules, J
• Power, P, is measured in Watts, W
• Time, t, is measured in seconds, s
• The power of an appliance can be calculated using the equation:
  Power (W)=Energy Transferred (J)Time (s)
• Appliances have power ratings in watts (W, kW)
• The kilowatt hour (kWh) is used as a unit of energy for calculating electricity bills.
• Electricity meters measure the number of units of electricity used.
• The more units used, the greater the cost.
• In fuel bills, the cost of electricity can be calculated using the equation:  Cost=Number of units used x Cost per uni
  t
• Work is done when charge flows in a circuit
• The power in an electric circuit can be calculated using the equation: Power W=Current A x Potential Difference V
• This equation can be represented as P = I x V
• The power transfer in any circuit device is related to the potential difference across it and the current through it, and to the energy changes over time
• The amount of energy transferred by an electric circuit can be calculated using the equation: Energy Transferred J=Current A x Time s) x Potential Difference (V
• This equation can be represented as E = ItV
• There is a relationship between the power ratings for domestic electrical appliances and the changes in stored energy when they are in use
• 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 = charge flow × potential difference (E = QV)
• The amount of energy transferred by electrical work can also be calculated using the equation: Energy Transferred J=Potential Difference V x Charge Flow (C)
• This equation can be represented as E = VQ
  
  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
• The National Grid system is an efficient way to transfer energy
• The potential difference or current in the coils of a transformer can be calculated using the equation:  Potential Difference across secondary coil Vx current in secondary coil A=Potential Difference across primary coil V x current in primary coil (A)
• This equation can be represented as VsIs= VpIp

Energy Resources

• The main energy resources available for use on Earth include fossil fuels (coal, oil and gas), nuclear fuel, biofuel, 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
• Some renewable resources can be replenished by human actions and some are replenished naturally
• A non-renewable energy resource is one that is not being (or can be) replenished as it is used
• Fossil fuels are non-renewable energy resources
• Examples of fossil fuels are coal, oil and natural gas
• Fossil fuels can be burnt to heat water, which produces steam. This steam can turn a turbine which powers a generator (generates electricity)
• The uses of energy resources include transport, electricity generation and heating
• Nuclear fuels release energy through nuclear reactions, which involve the breaking up of atomic nuclei
• Examples of nuclear fuels are uranium and plutonium
• The energy released through the nuclear reactions is used to heat water, which produces steam. This steam can turn a turbine which powers a generator (generates electricity)
• An advantage of fossil fuels is that they are reliable – they can always be used to generate energy. They also release lots of energy
• Disadvantages of fossil fuels are that they are non-renewable and burning them releases greenhouse gases which contribute to global warming
• Advantages of nuclear fuels are that they do not release greenhouse gases and they release lots of energy
• Disadvantages of nuclear fuels are that they are expensive to store and dispose of, and accidents carry a high risk to health
• Advantages of biofuels are that they are renewable and have low levels of harmful emissions
• A disadvantage of biofuels is that they require large areas of land to produce
• Advantages of wind energy are that it is renewable and doesn’t produce harmful emissions
• Disadvantages of wind energy include that the wind turbines look unattractive, they are noisy, they occasionally kill birds, and that it is unreliable (it’s not always windy)
• Advantages of hydroelectric energy are that it is renewable, it doesn’t produce harmful emissions and it’s reliable – it can be used to meet surges in demand
• Disadvantages of hydroelectric energy are that the dams are expensive to build, and they can damage local wildlife habitats
• Advantages of geothermal energy are that is renewable and doesn’t produce harmful emissions
• A disadvantage of geothermal is that it is expensive to drill far enough underground
• Advantages of tidal energy are that it is renewable, inexpensive to run, reliable and produces no harmful emissions
• A disadvantage of tidal energy is that it is expensive to build
• Advantages of solar energy are that it is renewable and has no harmful emissions
• Disadvantages of solar energy are that it is unreliable (as it’s not always sunny) and expensive to build
• Advantages of water wave energy are that it is reliable (as there are always waves), and no harmful emissions are produced
• Disadvantages of water wave energy are that it is expensive to build (lots are needed), and the equipment can be damaged by storms

Static Electricity

• 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
• 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

Disciplinary Knowledge

• Change the subject of an equation
• Interconvert units.

Practical Skills

• Safe use of appropriate apparatus to measure energy changes/ transfers and associated values such as work done

Internal Energy 

• Energy is stored inside a system by the particles (atoms and molecules) that make up the system. This is called internal energy 
• Particles in solids, liquids and gases have a store of kinetic energy because the particles are always moving or vibrating. The faster the particles are moving, the greater the store of kinetic energy. 
• Particles have a store of potential energy because their motion keeps them separated. The further apart the particles, the greater the store of potential energy.
• Internal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system. 

Thermal Transfer 

• 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. 
• When a substance changes state, the kinetic energy stays constant and the potential energy increases. 
• This is because energy is being used to overcome the forces of attraction between particles. 
• When a substance is heated but is not changing state, the energy in the kinetic store of the particles increases. 
• Heating and cooling curves can be used to show the temperature changes of a system as it is heated or cooled.
• When there is a temperature difference between objects or bodies in contact, thermal energy transfers from the hotter object (or body) to the cooler object (or body) until they reach the same temperature. When both objects reach the new temperature we say they have reached thermal equilibrium.  
• The greater the temperature difference, the greater the rate of thermal transfer. 
• Temperature is measure of the motion and energy of the particles.  
• Temperature is related to the average kinetic energy of the particles
• The SI unit for temperature is degrees Celsius (^oC) 
• When energy is transferred to an object by heating, its temperature depends on what the substance is made from, its mass and the amount of energy transferred.  
• Thermal conductors are materials that allow heat to move through quickly.  
• Thermal insulators are materials that only allow heat to travel through slowly. 
• Conduction is the thermal transfer by the vibration of particles. 
• Objects in a room will usually all be at room temperature.
• Some objects feel cooler than others because they are better thermal conductors. They transfer energy quickly away from the surface. 
• In conduction, the particles nearest to the heat source will vibrate first. These vibrations are passed onto the atoms next to them, which passes the vibrations through the material 
• Liquids and gases expand when they are heated. This is because the particles move faster and they take up more volume. The gaps between particles widen but the particles stay the same size 
• Metals are good thermal conductors because they have free (delocalised) electrons which can transfer thermal energy easily. 
• Convection is the thermal transfer when particles in a heated fluid rise.  
• During convection, the heated fluid becomes less dense and rises. The denser cold fluid falls into the warm areas forming a convection current.
• A fluid is a substance with no fixed shape – a liquid or gas. 
• Both conduction and convection require particles. 
• Radiation is the transfer of thermal energy as a wave, by infrared radiation. 
• Radiation does not require particles, so can occur in a vacuum 
• Some surfaces are better than others at absorbing and reflecting radiation  
• Shiny silvered surfaces are good at reflecting radiation. Dull, dark surfaces are poor at reflecting radiation 

Specific Heat Capacity

• Specific heat capacity is the energy required to heat 1 kg of a material by 1 ^oC
• The greater the specific heat capacity, the greater the amount of energy required to heat 1 kg of material by 1 ^oC
• Materials require different amounts of energy to heat up or change state
• Different materials will have different specific heat capacities
• The Greek letter delta is represented by the symbol Δ. In an equation it means ‘the change in’ or the difference between two values
• The Greek letter theta is represented by the symbol θ. In a specific heat capacity equation, it represents temperature
• The capital letter E represents thermal energy in the specific heat capacity equation, and is measured in Joules
• The lowercase letter m represents mass in the specific heat capacity equation, and is measured in kg
• The lowercase letter c represents specific heat capacity in the specific heat capacity equation
• Specific heat capacity is measured in joules per kilogram per degree Celsius (J/kg^oC)
• The change in thermal energy of a system can be calculated using the equation: Change in Thermal Energy J=Mass kg x Specific Heat Capacity J/kgºCx Change in Temperature (ºC)
• This equation is written as:  ΔE = m x c x Δθ
• To calculate specific heat capacity, the equation can be rearranged to c= ∆E÷m∆θ
• Objects with a larger mass or higher specific heat capacity require more energy to heat up

Specific Latent Heat

• Specific latent heat describes the energy required to change the state of 1 kg of a material
• Different materials have different specific latent heat values
• Specific latent heat of fusion refers to a change of state from solid to liquid
• Specific latent heat of vaporisation refers to a change of state from liquid to gas
• Specific latent heat of vaporisation is greater than the specific latent heat of fusion because more energy is required to overcome all the forces of attraction between the particles
• The uppercase letter L represents specific latent heat in the specific latent heat equation, and is measured in Joules per kilogram (J/kg)
• The change in thermal energy of a system can be calculated using the equation: Change in Thermal Energy J=Mass kg x Specific Latent Heat J/kg 
• This equation is written as:  ΔE = m x L
• Objects with a larger mass or higher latent heat capacity require more energy to melt or evaporate

Disciplinary Knowledge

• Change the subject of an equation
• Any anomalous values should be examined to try to identify the cause and, if a product of a poor measurement, ignored.

Forces

• A force is an interaction (e.g. push, pull or twist) between two objects
• Contact forces are where the objects are physically touching, such as friction, air resistance, tension and the normal contact force
• Non-contact forces, where the objects do not have to be physically touching, such as magnetism, electrostatic force and gravitational force
• Weight is the force acting on an object due to gravity. The force of gravity close to the Earth is due to the gravitational field around the Earth
• The weight of an object depends on the gravitational field strength at the point where the object is
• The weight of an object can be calculated using the equation: Weight (N) = mass (kg) × gravitational field strength (N/kg)
• Weight is measured using a Newtonmeter
• Weight will change if the gravitational field strength changes but mass will not
• The resultant force is the net force acting on an object, or the overall effect of all the forces acting on an object
• Balanced forces are when forces of the same magnitude act in opposite directions, cancelling each other out to produce a resultant force of 0 N

Speed

• Speed is how much distance is covered per unit time
• The speed of an object can be calculated using the equation: Speed (m/s)= Distance (m)Time (s)
• The SI unit for speed is m/s
• A stationary object has a speed of 0 m/s
• A distance-time graph can be used to describe an objects motion.
• A horizontal line represents a stationary object.
• A straight line represents an object moving at the same speed.
• A curved line describes an object accelerating

Scalars and Vectors

• Scalars are quantities which only have size
• Vectors are quantities with size and direction
• Examples of scalars include distance, speed, mass and energy
• Examples of vectors include displacement, velocity, acceleration, force, weight and momentum
• Velocity is speed in a given direction
• Displacement is how far an object is from its original position or from a point of reference in a given direction
• A resultant vector is the combination of two or more single vectors, such as resultant force
• Vectors acting in the same direction can be added together
• Vectors acting in opposite directions can be subtracted
• The resultant of two vectors at right angles to each other can be determined by calculation or by scale drawing
• A single force can be resolved into two components acting at right angles to each other. The vertical and horizontal component forces together have the same effect as the single force

Newton’s Laws

• Newton’s Third Law states that every action has an equal and opposite reaction
• This means that if object A exerts a force on object B, object B exerts an equal and opposite force on object A
• Newton’s First Law states that an objects motion will not change unless acted on by an unbalanced force (non-zero resultant force)
• An object is in equilibrium if the forces acting on it are balanced and the resultant force is 0 N
• A stationary object will stay stationary if the resultant force is 0 N
• An object in motion will stay moving at the same velocity if the resultant force is 0 N
• A stationary object will accelerate in the direction of the force if the forces are unbalanced
• A moving object will accelerate in the direction of the resultant force
• The tendency of objects to continue in their state of motion is called inertia

Acceleration

• Acceleration is the rate of change of velocity
• Acceleration is a measure of how quickly an object speeds up, slows down, or changes direction
• An object moving in a circle is constantly changing direction, therefore it is accelerating
• A negative acceleration, or slowing down, can be called deceleration
• The SI units of acceleration are (m/s²)
• Near the Earth’s surface any object falling freely under gravity has an acceleration of about 9.8 m/s²
• Air resistance/drag increases with speed
• The acceleration of an object can be calculated using the equation: Acceleration (m/s2)= Change in velocity (m/s)Time (s)
• The change in velocity can be calculated using the final velocity minus the initial velocity
• Velocity-time graphs can be used to describe motion
• A horizontal line indicates the objects velocity is constant
• A straight line with a positive gradient indicates the object is constantly accelerating (the velocity is increasing)
• A straight line with a negative gradient indicates the object is constantly decelerating
• The distance travelled can be found by calculating the area under the graph
• A curved line indicates the acceleration is changing
• The acceleration of an object can be found by calculating the gradient

Disciplinary Knowledge

• Understand that y=mx + c represents a linear relationship
• Change the subject of an equation
• Determine the slope and intercept of a linear graph
• Understand the physical significance of area between a curve and the x-axis and measure it by counting squares as appropriate.
• Any anomalous values should be examined to try to identify the cause and, if a product of a poor measurement, ignored.
• Recognise the importance of scientific quantities and understand how they are determined.

Practical Skills

• Measure time accurately
• Measure motion, including determination of speed and rate of change of speed (acceleration/deceleration)
• Plot two variables from experimental or other data