Energy & Efficiency
… Name 9 forms of energy.
… What does the word ‘potential’ mean, for example in Gravitational potential energy?
… Energy can move from one place to another, or can be …?… from one FORM to another.
… Energy cannot be c…?… or d…?… This is known as the “law of …?… of energy”
… Using a Sankey energy diagram to show how energy is transferred in a machine or process. Make sure that the width of each ‘energy arrow’ represents its energy value in Joules.
… Batteries convert …?… potential energy (stored) into …?… energy.
… Energy can be transferred into u…?… forms. However part of it is usually …?… and transferred to the s…?… which gets slightly warmer.
Because this wasted energy becomes more spread out, it becomes less u…?…
… The sun converts nuclear energy via fusion into …?… energy of the gases in the sun. These hot gases then emit e…?… radiation such as v…?… light, i…?…-r..?… and u…?… which travels through the vacuum of space to reach the Earth.
… What are the types of energy for the input and output of the following machines? Which are useful and which are wasted?
CD player
Torch
Clockwork toy
Bunsen burner
Hairdryer
… The equation to work out efficiency in terms of useful energy out and total energy in, is…?
… The equation to work out efficiency in terms of useful POWER out and total POWER in, is…?
Generating electricity
… Energy sources (for example fuels) can be used to …?… water to make …?… and drive t…?… connected to g…?….
… Methods of generating electricity by driving turbines directly include…?
… What are some advantages and disadvantages of generating electricity using Solar cells?
… Geothermal energy: in some volcanic areas hot w…?… and s…?… rise to the surface. The s…?… can be used to drive t…?… coupled to g…?…. which produce electricity.
… Advantages and disadvantages of various energy resources.
- What is the definition of a renewable resource?
- What are three major uses of energy resources?
- What are the pros and cons of wind energy electricity generation vs. energy from burning gas fired power stations?
- Describe the environmental issues that may arise from the use of different energy resources.
- Why might science not always be able to identify and solve environmental issues?
… How coal, oil and nuclear power form a ‘b…?… l…?…’ of supply to the national grid. Gas fired power stations are quick to turn on or off, so these help to cope with times of higher demand – for example each day in the morning.
… The advantages of using gas-fired power stations compared to coal-fired power stations:
• no sulfur dioxide released
• doesn’t cause acid rain
• no particulates released
• doesn’t cause global dimming
• less carbon dioxide released (per kg of fuel burned)
• less global warming
• no solid waste
• gas mining is less destructive than coal mining
… ‘Pumped Storage’ schemes can also store energy at …?… when the demand is low, by pumping water up to high reservoirs. During the day, they let the water fall back to the lower reservoir which turns …?… and generates electricity to cope with the extra electricity d…?….
… …?… power stations take the longest to start up or shut down. Why is this useful?
… Effects of generating electricity on the environment for different energy resources.
… Small scale electricity generation methods.
… Storing carbon dioxide using ‘C…?… C…?… Technology’ schemes.
… Why are transformers used in the National Grid electricity distribution network?
What is the equation which links the power lost due to electrical heating in a conductor to current flowing through it and its resistance?
… What are the advantages and disadvantages of pylons vs underground cables?
Waves
… Waves transfer …?… from one place to another.
… Oscillations in a longitudinal wave are …?… to the direction of the wave’s energy transfer.
… Oscillations in a transverse wave are …?… to the direction of wave’s energy transfer.
… Sound waves are …?…, electromagnetic waves are …?… and mechanical waves (e.g. on a slinky spring) can be either …?… or …?…
… Wavelength is the d…?… from one crest to the next in a transverse wave.
… Frequency is the number of o….?…. (wave vibrations) per second, measured in units of …?…
… Wave velocity = …?… × …?…
… Labelling the different parts of a wave
… Sound wave amplitude, frequency, wavelength and waveform. How do these affect pitch, loudness and quality of sound (the timbre)?
… Name 4 types of mechanical waves? Which are longitudinal and which are transverse?
… Longitudinal waves have areas of high-pressure called …?… and areas of lower pressure called …?…
… Sound is caused by v…?… which make pressure waves move through a substance such as air. The air particles oscillate …?… to the direction of wave travel.
… What is the range of audible sound frequencies for human?
… Soundwaves need a m…?.. (a fancy name for a material) to travel through. This means that soundwaves cannot travel through space (a v…?…).
… What experiment could you perform to calculate the speed of sound? How could you improve the accuracy of this experiment?
… The speed of sound can be measured using two microphones a set distance, D, apart and a single sound source.
Connecting the microphone electrical signal outputs to an oscilloscope enables us to view the longitudinal waves they are receiving as a transverse wave image on the screen.
As the oscilloscope enables us to ‘freeze’ the wave signals, we can measure the time difference, T, between a sound wave peak arriving at one microphone compared to the other.
Then the speed of sound can be calculated using speed = D/T
… The speed of sound in materials with strong bonds between their particles will be high. For example, the speed of sound in metal is much faster than in wood. Density does play a part too – if the particles are closer together, then they don’t need to move as far in order to transmit their kinetic energy to the next particle.
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… The electromagnetic spectrum (in order of increasing frequency and decreasing …?…) is…?
(Remember “Raw Meat Is Very Unhealthy eXcept Goat”)
… The range of wavelengths for electromagnetic waves is from 1000+m (r…?… waves) to 10^-15m (g…?… waves)
… Electromagnetic waves all travel through space (a v…?…) at the same …?… which is about 300 million metres per second!
… Light takes about 8 minutes to reach the Earth from the Sun. It would take about 171 years to drive his distance!
… If a surface is very smooth, the incident light rays will be reflected at similar angles and you will be able to see a reflected image.
If a surface is rough, then the reflected rays scatter in random directions (diffuse scattering) which means that images cannot be formed. The surface appears matt.
… The colour of an object is determined by which wavelengths of light it absorbs and which it transmits (i.e. reflects back).
… The higher the frequency (the …?… the wavelength) of electromagnetic radiation, the more …?… it transfers. This is why …?… rays (from radioactive material), x-rays (used in …?…) and …?… radiation (from the sun) can be harmful to living tissue.
… How are radio waves, microwaves, infrared and visible light used for communications?
… Evidence is now suggesting that microwaves emitted by devices such as mobile phones and wifi routers can be harmful to our bodies, even though microwaves are not ionising such as x-rays.
… Seismic S waves (transverse) originating from an earthquake travel around the surface of the Earth and also through the mantle. S-waves cannot travel through a liquid and so are stopped by the outer core of the Earth.
… Seismic P waves (longitudinal) travel through the mantle and core, refracting (speeding up or down and changing direction) as they move through a boundary between two different material densities.
… P-waves and S-waves provide evidence for the structure and size of the Earth’s core. For example, P-wave ‘shadow zones’ occur on the other side of the Earth to the original earthquake. These zones are due to the refraction effects at the mantle-outer core boundary.
Also, S-waves cannot travel through a liquid, and so are stopped at the mantle – liquid outer core boundary.
Diffraction:
… Diffraction is when waves …?… when they pass through a gap or go past an obstacle.
… If the w…?… is about the same size as the gap or object, then you will observe a lot of diffraction.
… Which will diffract more around a hill: radio waves or microwaves? Why?
… How longer wavelengths of low frequency sounds need to be produced by large diameter speakers (woofers) so that the wave diffract and spread out.
… How shorter wavelengths of high frequency sounds need to be produced by small diameter speakers (tweeters) so that the wave diffract and spread out.
Reflection:
… The Normal line is the line that is at …?… degrees to the surface at the point where the ray hits the mirror.
… The angle of …?… will always be equal to the angle of …?…
… What are the 3 properties of the image seen in a plane mirror?
Refraction:
… When a light ray crosses a boundary between two different materials, its …?… will change, and this might cause the ray to …?… This effect is called …?…
… For example, when a light ray travels from air into glass, water or Perspex, what will happen to its speed?
… It is essential to draw in the NORMAL line (the line which is perpendicular to the surface where the wave enters) before figuring out which way the ray refracts.
… How does the phrase ‘Speed Away’ help you to work out how the ray will refract?
… What do you think would happen to a ray of light which enters into a substance head- on along the normal line?
… The eye refracts light using the …?… lens and the crystalline lens (which is behind the …?…). Light rays are brought to a focus on the …?… at the back of the eye.
… What do shortsighted and longsighted mean?
… Total internal reflection is when the angle of incidence is greater than the critical angle (when a ray is trying to escape from glass)
… Applications of total internal reflection include:
Optical fibres for communications and in an endoscope.
‘Cats eyes’ in the road (to reflect car headlights and light the centre of the road)
Prisms to reflect the light in a periscope or a pair of binoculars.
… Dispersion (the splitting of white light into its constituent colours) occurs in a prism because different wavelengths of light travel at different speeds in a transparent material such as glass.
This means that violet light (which slows down the most) will refract through a larger angle than red light (which slows down the least).
The Expanding Universe
… What is a galaxy?
The Doppler Effect and Redshift:
… Red light has a …?… wavelength than blue light.
… The Doppler effect is when a source of waves (e.g. light from a distant galaxy) moves towards or away from an observer and this causes the light’s wavelength to change. If the wave source moves AWAY from the observer, then the wavelength will …?… and the frequency will …?…
… You can hear the Doppler effect when an ambulance passes by. When it comes TOWARDS us, the siren has a higher pitch because the wavelength of the sound is …?… (and the frequency …?…). When it moves AWAY from us, the siren has a lower pitch because…?
… Hubble discovered that further away a galaxy is from us, the …?… it is moving away from us (on average). He discovered this because the light from these distant galaxies was ‘…?…-shifted’.
… The light from most of the distant galaxies we view from Earth is …?…-shifted. This means that most of the objects we see in the night sky are moving AWAY from us. This observation provides evidence is that the universe is expanding in all directions (like a balloon).
At some point back in time, the universe must have been a tiny point, which suddenly expanded to form the universe that we see today. This theory is called the …?
… What has happened to the gamma radiation that was produced at the time of the Big Bang?
… What piece of evidence can only be explained by the Big Bang theory?
… Cosmic background microwave radiation (CMBR) is evidence for the …?… theory. We detect this microwave radiation coming from …?… directions in space. It started life as …?… rays that were emitted by a very hot, small and young universe. These rays were …?…-shifted to microwaves (wavelength stretched due to the Doppler effect) as the universe expanded.
Heat transfer
… Heat can transfer from one place to another by r…?… . For example, sunlight feels warm because your skin is receiving heat energy from i…?… – r…?… waves, which are part of the e…?… spectrum. These waves can travel through a v…?… such as in space.
… We calculated that it would take 171 years to drive to the sun! Light travels so fast (300,000 km/s) that Infrared rays and other electromagnetic waves take about 7 minutes to travel the same distance.
… Surface and colour affect how much infrared radiation is emitted and absorbed. Black Matt surfaces are …?… absorbers and …?… emitters of infra red radiation. Light shiny surfaces are …?… absorbers and …?… emitters (they are also …?… reflectors).
… A ‘black body’ is a perfect absorber (i.e. it doesn’t reflect) and emitter of radiation. Such a body must be in thermal equilibrium with its surroundings so that the rate of emission is equal to the rate of absorption.
… When you heat up a substance, what you would see happening to its particles?
… Which state of matter has the highest kinetic energy in its particles: liquid, gas or solid?
… Conduction is heat transfer through materials due to v…?… from one atom to another (and freely moving e…?… in the case of metals)
… …?… currents can form when fluids (…?… or …?…) are heated. The hotter fluid particles move around …?… and so they take up …?… space. As a result, the hotter fluid becomes …?… dense than the surrounding cooler fluid and so it will …?…
… Evaporation happens when particles of a liquid gain enough …?… energy to break their liquid bonds and escape as a …?…
… Evaporation causes cooling because only the …?… (hotter) particles escape, leaving the slower (…?…) particles behind in the liquid.
… Is thermal energy taken in, or given out when bonds are broken? How about when bonds are made?
…what four factors affect the rate of evaporation? Can you explain why?
… Condensation occurs when particles of a …?… lose k…?… energy by being c…?… down so they form l…?.. bonds.
When you answer questions in thermal physics, try to use as many relevant scientific words as possible. E.g. “Transfer, Radiation, Waves, Infra-red, Conduction, Vibrations, Move faster, Absorb, Emit…”. It’s always worth writing that extra sentence!
… Calculating the cost of heat lost through (for example) the roof of a house.
1) First add up all the joules of heat lost from the house.
2) Then work out the fraction (or percentage) lost through the roof (bit that you want out of the whole).
3) The multiply this fraction by the total cost of heating the house each year.
How to keep objects warm. This means minimising the heat transfer from the object to the surroundings by using design features such as:
- white shiny surfaces
- small surface area
- trapping air in pockets (e.g. fur)
- using materials such as plastic
Why do these design features help to keep an object warm?
… The specific heat capacity of a material is the amount of …?… needed to change 1kg of the material by a temperature of …?… degree Celsius.
This is why when the sun is shining on a sandy beach, the sand warms up to a higher temperature than the sea water. Sand has a much lower SHC than water and so heats up much more for the same energy input.
… The specific heat capacity equation is:
E = mcΔT
What do each of the letters stand for?
… The specific latent heat of fusion or vaporisation is the energy required to melt (or vaporise) 1 kg of material. This latent heat energy is used to increase the potential energy of atoms or molecules, NOT the kinetic energy. This means that during melting or boiling, the temperature of the material (which is a measure of the kinetic energy of the particles) remains constant.
… The equation linking specific latent heat, mass and energy released (or absorbed) is…?
… The greater the …?… difference between an object and its surroundings, the …?… the RATE at which thermal energy is transferred from one to the other.
…. The U-Value of a material tells us…? The lower the U-Value, the better the material is at being an …?…
… The RATE of heat transfer can be seen from the s..?… (or g..?…) of a temperature – time graph.
… Heat energy always flows from a hotter body to a …?… body.
Kinetic Theory of Matter
… Brownian motion is named after the botanist Robert Brown and can be seen by looking at smoke particles in air (or pollen grains on water) through a microscope. It provides evidence to support the kinetic theory of matter, which is that matter is made of tiny particles: atoms, ions or molecules.
… In a liquid or gas, the particles move at random.
… Brownish motion is the random motion of a smoke particle (or pollen grain) due to the fast-moving an invisible atoms or molecules colliding with the particle.
… At any one instant, there may be more collisions on one side of the smoke particle, and so the smoke particle moves in that direction.
Gas Laws
… Boyle’s Law states that pressure × volume of a fixed mass of gas held at a constant temperature will always be constant.
So pV of the gas in situation 1 = pV of the gas in situation 2
… The Pressure Law (Gay-Lussac’s law) states that pressure / temperature = constant if volume is held constant.
So p/T of the gas in situation 1 = p/T of the gas in situation 2
… The full gas equation incorporates temperature:
pV/T = constant
Where at is measured in Kelvin.
… The kelvin temperature scale
0°C = 273K
20°C = 293K
-273°C = 0K (‘absolute zero’)
… Gas law questions are fairly straightforward if you List your starting data (but watch out for the temperature in units of Kelvin!)
Electrical Applicances
… The power rating (units of …?…) of an appliance tells you how much …?… is transferred in each …?…
… Energy = P…?… × t…?…
… Energy can be measured using either:
“Domestic power” units of kilowatts (kW), hours (h) and kilowatt-hours (kWh), or
Standard units of Watts (W), seconds (s) and Joules (J)
… Domestic electricity calculation for how much a heater costs to run in one hour using E = P x t. Be careful to check that the units in your data List are correct (kWh, h, kW) as sometimes you may need to convert minutes into hours etc.
… Once you have calculated the number of kWh used (called ‘units’ of electricity) then remember to multiply by the cost per kWh to find the total cost.
… Well done for structuring your calculations using List-Equation-Solve-State 🙂
… When comparing the cost effectiveness of a new appliance (e.g. a new washing machine, or perhaps as a new machine for your business), what are 6 cost factors that you should consider?
… Calculating and comparing ‘payback time’ of various products, for e.g. Double glazing vs. cavity wall insulation.
Digital communications
… Analogue signals are continuously varying and can take any value between a minimum and maximum value.
… Digital signals can only take specific values, and usually one of only two levels: low, a “0” or high, a “1”.
… Converting analogue audio signals to digital.
Digital audio is recorded by taking samples of the original analogue wave at a specified rate, called the sampling frequency. For each sample, the voltage of the analogue signal at that time (e.g. from a microphone) is converted into a binary number.
The more levels you have at which to sample, the more accurately you can sample the waveform. For example, 16bit samples can convert an analogue waveform into 2^16 levels = 65536 voltage levels.
Also, the higher the sampling frequency, the more accurately you can sample the waveform. Generally, the minimum sampling frequency should be at least TWICE the highest frequency in the waveform. So that usually means sampling at 20kHz × 2 = 40kHz (standard sample rates start at 44kHz).
… When analogue or digital signals are transmitted, e.g. using radio waves, interference can degrade the signal which becomes ‘noisy’. In addition, the signal will attenuate over distance, meaning that the amplitude will decrease as the wave loses energy. Digital signals can be fully regenerated to remove the noise and attenuation without any loss of signal quality.
… Vinyl records store analogue information in the etched grooves. CDs store digital information in the form of ‘pits’ and flat areas that are detected by a laser.