Physics Module 1

What is heat?
A measure of internal energy - measured on the absolute scale - measured in J
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What is temperature?
A measure of the average kinetic energy of the particles in a substance - measured on the arbitrary scale - measured in *C
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What is specific heat capacity?
The amount of energy needed to raise the temperature of 1kg of substance by 1*C
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What is the specific heat capacity of water?
4200 J/kg/*C
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What is the equation for energy using specific heat capacity?
Energy (J) = Mass (kg) x Specific Heat Capacity (J/kg/*C) x Change in Temperature (*C)
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Why does the temperature plateau when a substance is changing state?
Heating - Energy is going into breaking the intermolecular bonds between particles and not raising temperature / Cooling - Intermolecular bonds are being formed between particles and so energy is being released.
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What is specific latent heat?
The amount of energy to required to change the state of 1 kg of substance without a change in temperature
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What is the equation for energy using specific latent heat?
Energy (J) = Mass (kg) x Specific Latent Heat
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What is conduction?
The process where vibrating particles pass on kinetic energy to neighbouring particles
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Why are metals good conductors?
Metals have outer electrons which are free to move throughout the metal. When heated, the electrons gain kinetic energy and they move faster throughout the metal transferring their energy to other electrons as they go. Heat transfers more efficiently
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Why do non-metal, liquids and gases make good insulators?
Non-metals don't have free electrons and so heating up takes longer / Liquids and gases conduct slowly because their particles aren't held tightly together so the amount of collisions is reduced
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What is convection?
When the more energetic particles move from the hotter region to the cooler region and take their heat energy with them
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How do grills cook their food?
Using infrared radiation - Heat radiated by the grill is absorbed by the surface particles of the food, increasing their kinetic energy. The energy is then conducted or convected to central parts.
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How do microwave ovens cook their food?
Using microwaves - The microwaves penetrate 1cm into the outer layer of the food where it's absorbed by fat or water molecules increasing their kinetic energy. Energy is conducted or convected to other parts
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Why don't you use foil in a microwave oven?
The microwaves will be reflected away from the food and could cause dangerous sparks. Plastic and glass are okay as the waves can pass straight through them
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What is the equation for payback time?
Payback Time = Initial Cost / Annual Saving
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How is cavity wall and insulation useful?
By having two layers of bricks with a gap between them, it prevents heat being lost by conduction however, it can still be lost by convection. The insulation foam traps pockets of air which minimise heat lost through convection
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What is the equation for efficiency?
Efficiency (%) = ( Useful Energy Output / Total Energy Input ) x 100
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What is the equation for wave speed?
Wave Speed (m/s) = Frequency (Hz) x Wavelength (m)
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What is 1 MHZ (megahertz) in Hertz?
1,000,000 Hz
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What is the law of reflection?
The angle of incidence always equals the angle of reflection
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How do you achieve total internal reflection?
Have the light ray travel through a dense material leading to a less dense substance. The angle of incidence must be bigger than the critical angle so that all of the ray if reflected back
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How does the size of a gap effect how much a wave is diffracted?
If the gap is very small, the wave is diffracted a lot. You achieve maximum diffraction when the gap is the same size as the wavelength
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How does an obstacle affect how much a wave is diffracted?
The wider the obstacle compared to the wavelength, the less diffraction there is and so the longer the obstacle's 'shadow'
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How do you refraction occur?
When a wave meets a new medium at an angle. If it travels into a denser medium, the wave slows down so it refracts towards the normal. If it travels into a less dense medium, the wave speeds up and so it refracts away from the normal
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List the seven EM waves and their uses
Radio - radio / Micro - mobiles / Infrared - cooking / Light - signals / UV - tanning / X-ray - x-rays / Gamma - sterilising equipment
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What are the limiting factors of using EM waves as signals?
Signals can be diffracted as they leave the dish. This causes problems as the waves spread out and so to reduce this, a larger dish is needed / Diffraction can distort the image you are trying to view in a telescope/microscope
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A - Almost instantaneous and can be sent using a torch / D - Can be easily seen by others and so needs to be coded for security
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A - Almost instantaneous. Can travel long distances and through the atmosphere. They can travel across space / D - Can be intercepted. Can be affected by interference
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A - Almost instantaneous and easy to use / D - Needs equipment and wires linking the sender and receiver. Wires can be damaged/cut. Signal requires amplification at regular intervals as energy's lost through heat due to current
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How can light be used in communication?
Light can be used in morse code - a series of on/off signals with dots and dashes that represent letters / It can be used in optical fibres. If sent at an angle greater than the critical angle, the light totally internally reflects along the fibre
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What are the advantages of using light in communication?
Very quick / Multiplexing - lots of signals can be sent at once / Little Interference - digital signal
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What properties does a laser have?
All the waves are in phase with each other / waves have the same frequency / have low divergence / this produces a coherent, monochromatic light
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What are the uses of lasers?
Precision cutting in industry / Surgery and Dental / Measuring distances / Reading a CD
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How do CD players work?
CDs have many pits engraved into its surface. A laser is shone onto the CD and light reflects back at slightly differently due to lands and pits. The differences are changed into electrical signals. Change in reflection = on - No change = off
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What uses does infrared have around the house?
Cooking / Remote controls / Mobile phones and Computers over short distances / Security Systems - detects body heat signatures / Optical Fibres
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How can infrared be used to monitor heat?
Infrared is heat radiation. This means infrared sensors can be used to detect this heat. This can be used in night-vision technology as well. The equipment turn it into electrical signals which can be displayed as an image
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How can IR signals control electrical equipment?
Remote controls emit pulses of IR to devices such as a TV. The pulses act as a digital code (on/off) and the device decodes the signal and follows the set instruction that's assigned to it e.g play or pause. Mobiles and computers do this also
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What are the disadvantages of using IR to control electrical equipment?
You need to be close for it to work as the IR pulses from a small, low-powered remote are fairly weak / The beam must be pointed straight at the detector as IR waves only travel in straight lines
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Why are radio and microwaves good at transferring information over long distances?
This is because they don't get absorbed by the Earth's atmosphere as much as waves in the middle or at the end of the EM spectrum
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How do short wave radio signals travel long distances?
The waves can reflect off of the ionisphere and Earth's water surfaces. This means the wave behaves as if it is total internal reflection and so can travel across the world
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As they are very short, they must be in line of sight of their receptor as they cannot diffract far around obstacles or travel far through houses
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Why can long radio waves travel long distances?
This is because the long wavelength is large in comparison to the gap meaning it can diffract a lot when it meets an obstacle and so can bend around them and corners meaning the receiver doesn't have to be in line of sight of the transmitter
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What troubles do short radio waves and microwaves face?
As their wavelength is shorter, they don't diffract a lot so transmitters must be placed high up to avoid obstacles - areas won't get reception / Diffraction can occur at the edge of the dishes, spreading the wave out and so the signal is weaker
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Why do short-wave and medium wave radio signals reflect off of the ionosphere?
The ionosphere has a different density to non-ionised areas. Radio waves speed up in the ionosphere but are slower beneath it making radio waves refract. Short-wave radio signals don't refract as much as medium waves - higher angle of elavation
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Why do radio waves suffer interference?
There are limited radio frequencies that transmit a good analogue signal so radio stations often broadcast with similar frequencies. This means they interfere with each other in a similar area as they can combine creating noise
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DAB allows many signals to be compressed and transmitted as a single wave known as multiplexing. The combined wave is the separated out be a demutiplexer at the end of transmission.
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What are the advantages of DAB?
All the signals are being sent from many stations at the same frequency (multiplexing) meaning they can't interfere with each other. This means more radio stations can open up without the fear of inteference
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What are the disadvantages of DAB?
There are a limited number of DAB transmitters in the UK so some areas won't receive digital radio at all / DAB sound quality is not as good as a traditional radio broadcast due to the signal compression
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How are microwaves used for satellite communication?
Signal's sent from a transmitter into space where it's picked up by the satellite's receiver dish orbiting the Earth. The satellite transmits the signal back to Earth in a different direction where it's received by a satellite dish on the ground
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Why are microwaves used for satellite communication?
Microwaves have a wavelength which can easily pass through Earth's watery atmosphere without too much absorption. This means it can be used by remote sensing satellites - they see through the clouds to track oil spills, rate of deforestation etc.
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How do mobile phones transmit signal?
Mobiles transmit calls as microwaves to the nearest transmitter or mast. The transmitter pass signals between each other then back to your mobile phone
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Why do large objects effect signal strength in mobiles?
Microwaves have shorter wavelengths than radio waves and so they don't diffract much so if they come across a large obstacle, the microwaves cannot bend around it.
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What is done to improve signal strength?
Most transmitters are positioned in 'line of sight' - high up and close together however, if there is still a hill or a man-made sculpture in the way, you'll still get little to no signal
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What happens if you and your phone are near water?
Even though they can travel through the atmosphere, microwaves are still partially absorbed by water . So in adverse weather or if you're by a lake, signal is lost through absorption or scattering
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How are microwaves from microwave ovens a potential threat?
They are absorbed by water molecules in food so in theory, if water molecules are absorbed by water molecules in living tissue, cells may be burned or killed
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What are the conflicting attitudes to mobile phones and masts?
Some people think the microwaves emitted into your body from your phone or mast could damage health / There is no conclusive proof - lots of conflicting evidence / Any potential dangers would be due to increased exposure time - living near a mast
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Why does the size of the receiver depend on the size of the wave?
As a wave enters a receiver, it goes through a gap. Gap = same size as the wavelength, the wave's diffracted and detail's lost. As gap size increases, diffraction decreases. The bigger the receiver compared to the wave, the clearer the information
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How do radio telescopes get over low resolution?
Radio telescopes are often linked together and have their signals combined to get more detailed information. Bigger receivers can collect more EM waves and so give a more intense image
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What is meant when a telescope is diffraction limited?
The telescope has a smaller gap than compared to the wavelength they're looking for and so have a limited resolving power
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Why do optical microscopes have to be small?
You use them to look at small smaples in the lab and so you only want to collect light from a small area only.
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What is a fault with optical microscopes?
Their small size makes it hard to get a good resolution - the gap has to be really small so you still get some diffraction even though light has a small wavelength
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What is interference?
When 2 or more waves of a similar frequency meet, they can create one combined signal with a new amplitude
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What advantages do digital signals have over analogue signals?
If both signals have suffered interference, it is easier to remove from digital as there are only 2 values and so remains a high quality but analogue noise is just amplified and so loses quality / digital can allow multiplexing
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What are the problems associated with staying in the sun too long?
Sun contains UV radiation which if exposed for a long time can damage DNA in cells and so increases the risk of skin cancer / UV radiation can cause eye problems - cataracts / UV can lead to premature skin aging
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Why are darker skinned people protected more than paler people?
Their dark skin lets them absorb more UV radiation than compared to a pale person and so prevents some of the damaging radiation reaching more vulnerable tissues deeper in the body
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What does SPF mean?
Sun Protection Factor - the number next it says how many times as long you are allowed to saty out in the sun if you keep applying it e.g 15 SPF = 15 x as long
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How are the government trying to protect the public from overexposure to UV?
Research has been made public through media and advertising campaigns and we're told how to keep to improve public health. Also Tanning salons now have time limits to make sure people aren't over-exposed
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How do the ozone layer protect us and what is happening to it?
The ozone layer absorbs some of the UV radiation limiting the amount that reaches Earth meaning lower levels of exposure. However, it is depleting due to CFCS which react with ozone and break them apart. The depletion means more UV is reaching us
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What is the hole in the ozone layer?
In winter over Antarctica, the concentration of ozone goes down due to special winter effects. Over the years it has been dropping. The low concentration makes it look like a hole on satellite images
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How do we know what causes ozone depletion?
Several scientists with different equipment carried out tests to find out why the ozone was depleting in Antarctica. After making hypotheses and carrying out tests, they got accurate results showing CFCs were the problem and so they're now banned
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What are the two types of seismic wave and what are their properties?
P - longitudinal, the vibrations are along the direction the wave travels - these travel fatser than S and can go through liquids and solids / S - transverse, the vibrations are at right angles to the direction the wave is going - travels in solids
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How can seismic waves be useful?
They can tell us the structure of the Earth by where they turn up and where they're not felt. No s-waves in core's shadow means that the outer core is liquid. P-waves travel faster through the middle of the core suggesting that it's solid
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Why do seismic waves curve?
The waves change speed as the properties in the mantle and core change. This causes the wave to change direction - refraction. Wave speed normally changes gradually but if there is a sudden change in density, it causes a kink in the path
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Other cards in this set

Card 2

Front

What is temperature?

Back

A measure of the average kinetic energy of the particles in a substance - measured on the arbitrary scale - measured in *C

Card 3

Front

What is specific heat capacity?

Card 4

Front

What is the specific heat capacity of water?

Card 5

Front

What is the equation for energy using specific heat capacity?