3.20 describe the role of total internal reflection in transmitting information along optical fibres and in prisms
Total Internal Reflection:
- Used to transmit signals along optical fibres.
3.21 explain the meaning of critical angle c
Critical Angle:
- The angle of incidence which produces an angle of refraction of 900 (refracted ray is along the boundary of the surface).
- When the angle of incidence is greater than the critical angle, total internal reflection occurs (all light is reflected at the boundary).
- This effect only occurs at a boundary from a high refractive index material to a low refractive index material.
3.22 know and use the relationship between critical angle and refractive index:
also remember:
critical angle = sin-1(1/n)
3.23 know that sound waves are longitudinal waves which can be reflected and refracted
sound waves are longitudinal waves which can be reflected and refracted.
3.24 know that the frequency range for human hearing is 20–20 000 Hz
the frequency range for human hearing is 20–20 000 Hz
3.26 understand how an oscilloscope and microphone can be used to display a sound wave
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With the microphone plugged into the oscilloscope and a sound incident on the microphone, the microphone will transfer the sound into an electrical signal which the oscilloscope can display .The x axis show the time base which can be adjusted for example 2ms for 1 square so time period and frequency can be calculated from this, along the y axis voltage is displayed as the wave is converted into an electrical signal this means amplitudes can be compared. |
3.28 understand how the pitch of a sound relates to the frequency of vibration of the source
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High frequency means high pitch. If a string vibrates with a higher frequency then the note sounds higher. |
3.29 understand how the loudness of a sound relates to the amplitude of vibration of the source
The greater the amplitude the louder the sound. Bigger vibrations of a sting mean more energy is being put in so more energy out as sound waves.
4.01 use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s) and watt (W)
know the units for
Mass = kilogram (kg)
energy = joule (J)
velocity = metre/second (m/s)
acelleration = metre/ second 2 (m/s2)
force = newton (N)
time = second (s)
power = watt (W)
4.02 describe energy transfers involving energy stores: energy stores: chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear and energy transfers: mechanically, electrically, by heating, by radiation (light and sound)
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Energy Stores: Chemical – e.g. the food we eat Kinetic – movement energy Gravitational – objects that are lifted up Elastic – e.g. from springs Thermal – from hot objects Magnetic – objects in magnetic fields Electrostatic – charged objects Nuclear – stored within a nucleus
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4.03 use the principle of conservation of energy
In any process energy is never created or destroyed. (It is just transferred from one store to another.)
4.05 describe a variety of everyday and scientific devices and situations, explaining the transfer of the input energy in terms of the above relationship, including their representation by Sankey diagrams
The energy flow is shown by arrows whose width is proportional to the amount of energy involved. The wasted and useful energy outputs are shown by different arrows.
4.06 describe how thermal energy transfer may take place by conduction, convection and radiation
Conduction is the transfer of thermal energy through a substance by the vibration of the atoms within the substance. Metals are good conductors because they have free electrons that can move easily through the metal, making the transfer of energy happen faster.
Convection occurs in a liquid or gas. These expand when heated because the particles move faster and take up more volume – the particles remain the same size but become further apart. The hot liquid or gas is less dense, so it rises into colder areas. The denser, colder liquid or gas falls into the warm areas. In this way, convection currents are set up which transfer heat from place to place.
Thermal radiation is the transfer of energy by infrared (IR) waves. These travel very quickly in straight lines.
4.08 explain how emission and absorption of radiation are related to surface and temperature
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– Light, shiny surfaces are good reflectors of IR and so are poor at absorbing it. – Dark, matt surfaces are poor reflectors and good at absorbing IR. – This means that placed next to a heat source, a dark object would heat up faster than a light one. – Dark matt surfaces are also best at emitting IR. This means that a hot object with a light shiny surface will emit less IR than a dark matt object at the same temperature. – Hotter objects emit more IR per second. The type of EM wave emitted also changes with temperature – the higher the temperature the higher the frequency of EM wave emitted. |
4.10 explain ways of reducing unwanted energy transfer, such as insulation
A good insulating material is a poor conductor that contains trapped air, e.g. foam, feathers, glass fibre. Being a poor conductor (non-metal) prevents heat transfer by conduction and the trapped air prevents convection currents.
4.11 know and use the relationship between work done, force and distance moved in the direction of the force: W = F × d
Work Done (J) = Force (N) x distance moved (m)
4.12 know that work done is equal to energy transferred
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Work done = energy transferred |
4.13 know and use the relationship between gravitational potential energy, mass, gravitational field strength and height: GPE = m × g × h
Gravitational potential energy (J) = Mass (kg) x gravitational field strength (N/kg) x height (m)
4.14 know and use the relationship: kinetic energy = 1/2×m×v^2
Kinetic energy (J) = 0.5 x mass (kg) x velocity (m/s) 2
4.15 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work
Because energy is conserved the decrease in GPE = increase in KE, for a falling object if no energy is lost to the surroundings
4.16 describe power as the rate of transfer of energy or the rate of doing work
power is the rate of transfer of energy, or the rate of work done. so p = E/t
5.01 use the following units: degree Celsius (°C), Kelvin (K), joule (J), kilogram (kg), kilogram/metre3 (kg/m3), metre (m), metre2 (m2), metre3 (m3), metre/second (m/s), metre/second2 (m/s2), newton (N) and pascal (Pa)
The units for:
temperature: degree Celsius (°C) or Kelvin (K)
Energy: Joule (J)
mass: Kilogram (kg)
density: kilogram/metre cubed (kg/m3)
distance: metre (m)
area: metre squared (m2)
volume: metre cubed (m3)
velocity: metre per second (m/s)
acceleration: metre per second squared (m/s2)
force: newton (N)
pressure: pascal (Pa)
5.02 use the following unit: joules/kilogram degree Celsius (J/kg °C)
the unit for
specific heat capacity: joules/kilogram degree Celsius (J/kg °C)
5.03 know and use the relationship between density, mass and volume:
Units of density depend on units used for mass and volume:
E.g. mass in [g] and volume in [cm3] gives density in [g/cm3], however mass in [kg] and volume in [m3] gives density in [kg/m3].
5.04 practical: investigate density using direct measurements of mass and volume
- The density of an object can be found by measuring the mass and volume and applying the formula above to calculate the density.
- For a regular object use a ruler to measure the lengths needed to determine the volume.
- For an irregular object submerge it in water and measure the displaced volume.
- Measure the mass of either type of object using a measuring balance.
5.05 know and use the relationship between pressure, force and area:
pressure (Pa) = force (N)/ area (m2)
- Pressure is defined as force per unit area.
- One pascal (Pa) is equivalent to one N/m2
5.06 understand how the pressure at a point in a gas or liquid at rest acts equally in all directions
Pressure in liquids:
Pressure in liquids acts equally in all directions as long as the liquid is not moving.
5.07 know and use the relationship for pressure difference: p = h × ρ × g
Pressure difference [Pa] = Density [kg/m3] x g [N/kg] x Height [m]
ΔP = ρ g h
- The equation can be used in liquids or gases provided you know their densities.
P1 – Patm = ρ g h
P1 = ρ g h + Patm
5.10 describe the arrangement and motion of particles in solids, liquids and gases
solids:
- Tightly packed
- Held in fixed pattern
- Vibrate about fixed positions
liquids:
- Tightly packed
- Can slide over each other
gasses:
- Very spread out
- Move with rapid, random motion
5.11 practical: obtain a temperature–time graph to show the constant temperature during a change of state
- Remove the boiling tube of stearic acid from
the water bath - Place the tube into a beaker of room
temperature water - Add a separate thermometer to the water
- Take readings from the thermometer in the
stearic acid and the water every minute
[Make sure to avoid parallax error while doing so] - Note readings in the table below
- Note on the table when you observe the stearic
acid change from a liquid to a solid. - Plot your results in a graph
5.12 know that specific heat capacity is the energy required to change the temperature of an object by one degree Celsius per kilogram of mass (J/kg °C)
Specific heat capacity:
- Amount of heat energy required to increase the temperature of 1kg of a substance by 10
- Unit J/kg 0C
5.13 use the equation: change in thermal energy: ΔQ = m × c × ΔT
Change in thermal energy [J] = Mass [kg] x Specific heat capacity [J/kg 0C] x Change in temperature [0C]
5.14 practical: investigate the specific heat capacity of materials including water and some solids
- Set up the apparatus as shown the diagram.
- Make note of all measurements: current (A), potential difference (V), mass (kg).
- Use the electronic balance to measure the mass of your
- Record the initial temperature of you block.
- Switch on the heater and start your stopwatch.
[You will now leave the heater on for 10 minutes] - While the heater is switched on take readings from the
Ammeter and the Voltmeter. - Use these to calculate the Thermal Energy that will be
supplied to the block in 10 minutes - Record the temperature of your block after 10 minutes.
- Calculate the Change in Temperature
5.15 explain how molecules in a gas have random motion and that they exert a force and hence a pressure on the walls of a container
Gas laws:
- Gas molecules have rapid and random motion.
- When they hit the walls of the container, they exert a force.
- Pressure = Force/Area
5.16 understand why there is an absolute zero of temperature which is –273 °C
Absolute zero:
- At absolute zero the particles have no thermal energy or kinetic energy, so they cannot exert a force.
- Absolute zero = 0 Kelvin = -2730C
5.17 describe the Kelvin scale of temperature and be able to convert between the Kelvin and Celsius scales
0 K = -273 0C
E.g. 100K = -1730C
2000C = 473K
5.18 understand why an increase in temperature results in an increase in the average speed of gas molecules
As you increase the temperature of a gas, the kinetic energy of the gas particles increases and thus their average speed also increases.
5.19 know that the Kelvin temperature of a gas is proportional to the average kinetic energy of its molecules
The Kelvin temperature of a gas is proportional to the average kinetic energy of its molecules.
5.20 Explain, for a fixed amount of gas, the qualitative relationship between: pressure and volume at constant temperature, pressure and Kelvin temperature at constant volume.
- As you heat the gas, the kinetic energy of the particles increases, and thus so does their average speed.
- This means more collisions per second with the walls, and they exert a larger force on the wall.
- This causes in the total pressure being exerted by the particles to rise.
- If temperature is constant, the average speed of the particles is constant.
- If the same number of particles is placed in a container of smaller volume they will hit the walls of the container more often.
- More collisions per second means that the particles are exerting a larger force on the wall over the same time, so average force exerted on the walls has increased.
5.21 use the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume:
P1/T1 = P2/T2
*Temperature must be in Kelvin
Temperature law:
For a fixed mass of gas at constant volume, the pressure is directly proportional to the Kelvin temperature