Heat is a measure of energy in an object on an absolute scale
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What is heat measured in?
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Why is heat measured on an absolute scale?
Because the value of a particles energy (movement) cannot go below 0
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Describe how heat flows
Energy flows from a hotter medium to a cooler one to balance the temperature
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Temperature is a measure of the average kinetic energy of particles in a substance (how hot it is) measured on a scale that is not absolute
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What is temperature measured in?
degrees Celcius, Fahrenheit, Kelvin etc.
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Why is temperature not measured on an absolute scale?
Because temperature values can drop below 0 (freezing)
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What is Specific Heat Capacity?
The amount of energy needed to raise the temperature of 1kg of a substance by 1 degree Celcius (how much energy it can store)
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What is SHC measured in?
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Give the equation for Specific Heat Capactiy
Energy = Mass x SHC x Temperature Change
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How much energy is needed to heat 2kg of water from 10 to 100 degrees C? (SHC of water is 4200 J/kg/dC)
756 000 J
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Describe the time-temperature graph involved with heating water from -20 to 120dC
Temp. rises from -20 to 0 then gradient goes flat (no temp change) as energy is used to break intermolecular bonds instead of raising the temperature. the same happens at 100 dC when boiling
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Define Specific Latent Heat
The amount of energy needed to change the state of a substance without changing its temperature
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Give the equation for SLH
Energy = Mass (kg) x SLH (J/kg) - (note, SLH is specific to each substance for one state change)
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The SLH of water for melting is 334 000 J/kg. How much energy does it take to evaporate 200g of water? (remember to convert to the correct units)
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List the three ways energy is transferred
Conduction, convection and radiation
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How does energy travel by conduction?
Vibrating particles pass on kinetic energy to nearby particles to pass energy throughout a substance
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Through what medium does conduction generally occur fastest? Why?
Solids because the particles are tightly packed
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How does energy travel through liquids and gases by convection?
Particles with high relative energy move from the hotter region of a substance to the cooler region and take their energy with them before cooling and falling back to the hotter area
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How does energy travel by radiation?
Electromagnetic waves carry energy without needing a medium
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What surfaces best absorb and emit heat radiation
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Describe how food is cooked in an oven
Heat is emitted as infrared waves by the black panels on the inside and reflects around making sure all the food is cooked
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Describe how is food cooked in a microwave oven
Microwaves are emitted at the food penetrating roughly 1cm in and heating water and fat molecules only. These molecules then spread their energy throughout the rest of the food by conduction
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List 5 methods of reducing energy loss in a house
Loft insulation, cavity wall insulation, double-glazed windows, thick curtains and draught-proofing
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What is payback time?
The amount of time it takes for an energy saving device to pay itself off
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How can a Thermogram be used to show energy wastage?
A thermal imaging camera turns infrared emission into an image showing where heat is escaping from a house with different colours depending on degree of emission to indicate what measures are needed
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How is energy usage of a device shown?
A Sankey diagram
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What is the equation for a device's efficiency?
Efficiency = (Useful energy output / Total energy input) x 100
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A kettle is supplied with 180 000 J of electrical energy. 9000 J is wasted by heating surrounding air. What is the kettles efficiency
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A light bulb has an efficiency of 5%. If 1000 J of useful light energy is given out, how much energy is wasted?
19 000 J
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If a device has efficiency higher than 50%, which arrow on a Sankey diagram will be thickest?
The one pointing right (useful output)
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List four measurable properties of a wave
Amplitude, frequency, wave length and speed
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The perpendicular height of the wave to the normal
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The number of complete cycles (or oscillations) passing a certain point per second
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The length of the full cycle of a wave e.g. crest to crest
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How do you calculate a wave's speed?
Frequency (Hz) x Wavelength (m)
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What Greek letter represents wavelength?
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All waves can be...
Reflected, refracted and diffracted
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What are the equivalents of crests and troughs in longitudinal waves?
Compressions and Rarefactions
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Angle of incidence equals...
Angle of reflection
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What is Total Internal Reflection?
When light hits a boundary of an optically less dense medium to the one it was in at an angle greater than the critical angle
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What happens if the angle of incidence equals the critical angle?
The ray travels along the boundary with some internal reflection
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What happens if the angle of incidence is less than the critical angle?
Most of the light leaves the medium but refracts away from the normal and some internally reflects
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A wave spreading out at the edges when passing through a gap
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What happens when the gap is the same size as the wavelength?
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Different parts of the wave change at different times when going from media of different optic densities. This causes the wave to bend
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When entering an optically more dense medium, which way does the wave bend?
Towards the normal
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List the seven types of electromagnetic wave in order from largest to smallest wavelength
Radio waves, Microwaves, Infrared, Visible light, Ultraviolet, X-rays and Gamma rays
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What effects can electromagnetic waves have when absorbed?
Heating and ionisation (if they have enough energy)
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The properties of an electromagnetic wave depend on what?
Frequency and wavelength
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Which waves tend to be more dangerous?
Higher frequency, short wavelength waves e.g. gamma because of high energy
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Give advantages of communication by copper cable and fibre optics
Can carry multiple pieces of information at once quickly, no signal loss like wireless, more secure than wireless systems, bigger bandwidth available cheaply
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Give advantages of wireless communication
Damaged cable can be expensive to repair and wireless is more practical over long distances, also makes devices portable
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How does information travel through optical fibre?
Light signals are sent down the fibre in bursts to make a binary code. The light travels by Total Internal Reflection
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What is multiplexing?
Several digital signals being sent down the same line at the same time in a sequence that can be decoded at the other end. This requires less cable and removes interference
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Which types of EM waves are used for transmitting information over long distances?
Radio and microwave
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How are short wavelength radio waves used in communication?
They can be reflected off the ionosphere to relay information from one part of the Earth's surface to another
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How are longer wavelength radio waves used?
The can diffract (bend) around the Earth's surface and around obstacles like mountains
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Which kind is used for FM radio and regular TV?
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Because they must have line-of-sight - little diffraction but can reflect
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How can diffraction cause signal loss at receptor dishes?
Waves can spread out at he edges of a dish making the signal weaker
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How exactly do radio waves 'reflect' off the ionosphere?
By refraction - waves speed up through ionoised particles so they bend back towards the Earth's surface
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What type of EM waves are used to communicate with satellites?
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Because their long wavelength means they aren't absorbed or scattered extensively when passing through the atmosphere
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What else are they used for?
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Why are mobile signal masts placed on high ground and close together?
Because microwaves cannot diffract - must have line of sight
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Why do some people think that living near telephone masts can damage your health?
Some studies suggest that absorption of microwaves can harm cells and cause mutations with prolonged exposure
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What does LASER stand for?
Light Amplified by Stimulated Emission of Radiation
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Give four properties of a laser
Monochromatic, in-phase, narrow beam, little divergence, coherent
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How are lasers used to read CDs?
A laser is fired at the surface, reflects off pits and flats and returns to the receiver as a binary sequence
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The size of a wave receiver is relative to what?
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Bigger receiver relative to wavelength reduces signal loss by diffraction
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Give three uses of infrared besides cooking
Controlling electrical devices e.g. TV remotes, motion sensor lights, thermal imaging, security systems
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What's the difference between digital and analogue signals?
Analogue can have any value within a certain range, digital has only two values (on/off)
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Give advantages of using digital signals
Multiplexing, interference doesn't affect quality
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Give advantages of analogue signals
Usually higher quality due to range vary
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Explain why Morse Code is a digital signal
It only has two values
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What problems can UV radiation cause?
Skin cancer due to mutations and cataracts
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What absorbs UV radiation to protect us?
The Ozone Layer
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What does SPF stand for?
Sun Protection Factor
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If someone can stay in the sun for 35 minutes without burning, how long can they stay in the sun with SPF 15 sun cream without burning?
8 hours 45 minutes
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What has damaged the ozone layer in the past
Use of CFCs in refrigerators and aerosols deplete ozone
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Fast Longitudinal waves that travel through solids and liquids. Detected first around the Earth and refract through denser media
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Slower transverse waves that cannot travel through liquid and are detected second
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How can we prove the outer core is liquid?
S-waves are not detected opposite the epicentre meaning they must travel through liquid
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Other cards in this set
What is heat measured in?
Why is heat measured on an absolute scale?
Describe how heat flows