Physics P1

Heat is a measure of energy

• When heated, substance gains KE.
• Energy is measured on an absolute scale. 
• Measured in Joules (J).

Temperature is a measure of hotness

• Temperature is a measure of average KE.
• If there is a difference in temperature between tow places, then energy will flow between them.

Specific Heat Capacity

• Tells you how much energy stuff can store.
•  Water has SHC of 4200 J/kg(deg)C.

Energy = Mass x SHC x Temp Change

Put in energy to break Intermolecular Bond

• When heated, particles move faster. When they have enough they overcome attraction to one another. Gas forms, liquid is boiling.
• Same happens in solid, except melting happens.
• Energy is used to break intermolecular bonds.
• When freezing or condensing, bonds are forming which releases energy.

Specific Latent Heat

• The SLH is the amount of energy neede to melt 1kg of material without changing the temperature.
• It should be at melting point already.
• Different for all materials.

Energy = Mass x Specific Latent Heat

Conduction occurs mainly in solids

• Particles vibrate, causing the others near to vibrate, passing vibration on.
• Particles pass on KE to neighbouring particles.

Conduction of heat is the process where vibrating particles pass on extra kinetic energy to neighbouring particles.

• Metals conduct well due to free electrons that move faster and collide with other free electrons. Faster than particles due to size.
• Non-metals don't have free electrons, vibrations passed on slower.

Convection occurs in liquids and gasses

Convection occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them.

• Radiators use convection.

Radiation is how we get heat from the Sun

• Heat is radiated as infared waves - these are electromagnetic waves that travel in straight lines at the speed of light.
• Radiation doesn't need a medium, can travel through a vacuum.
• Can only occur through transparent substances.
• Depends on surface colour and texture of object (absorbtion and emitting).

All objects emit and absorb heat radiation

Heat radiation is important in cooking 

• Grills and toasters use IR radiation to heat food.
• Microwaves use, well, microwaves (electromagnetic waves). They heat fat or water molecules.
• Foil reflects microwaves and can be dangerous.

Insultaing your house saves energy and money.

• Things that emit energy are called sources, things that transfer, lose or waste energy are called dinks.
• Insultaing houses prevents heat loss.
• Eventually the cost of insulation will be less than the amount of money saved, this is called payback time.

Types of insulation are:

• Loft insulation
• Cavity walls ( and insulation )
• Double Glazing
• Thick curtains.

Thermograms show where the house is leaking heat.

• Red and warm tone colours indicate lots or some heat loss, blue and cool tones indicate no or little heat loss. 

Machines always waste some energy

• Machines are only useful because they convert energy from one form into another, eg chemical to KE (cars).
• Total energy output is always the same as the energy input but only some is useful.
• Some energy is always wasted as heat and/or sound and such. 
• The less energy wasted, the more efficient the device is.

Energy = (Useful Energy Output / Total Energy Input) x 100

Waves have amplitude, wavelength and frequency

• The amplitude is the displacement from the rest position to the crest.
• The wavelength is the length of the wave (crest to crest).
• Frequency is the number of waves that pass a point every second.

Wave Speed = Frequency x Wavelength

1 kHz = 1000 Hz

1 MHz = 1 000 000 Hz

All waves can be reflected, refracted and diffracted.

• Waves travel in a straight line until they meet an obstacle where their direction can be changed.
• This can happen by reflection, refraction or diffraction.

Reflection of light lets us see things.

• Light bounces off an object. If it is an uneven surface, the light reflects off at different angles. 

The Law Of Reflection: Angle of Incidence = Angle of Reflection

Total internat reflection depends on the critical angle.

• This happens when a light ray travels through a dense material like glass towards a ess dense substance like air.
• If the angle of incidence is big enough, the ray reflect back and does not escape the medium.
• "Big enough" means bigger than the critical angle.

Diffraction - Waves spreading out

• All waves difffract at the edges when they pass through a gap or pass an object.
• The amount of diffraction depends on the size of the gap relative to the wavelength of the wave.
• The narrower the gap, or the longer the wavelength, the more the wave spreads out.
• Whether the gap is narrow depends on the wave. Light has a small wavelength so can be diffracted through a tiny gap.

Refraction - Changing the speed of a wave can change its direction

• Waves travel at different speeds in substances that have different densities.
• When a wave crosses the bodary between two substances, it changes speed.
• Waves are only refracted if they meet a new meduim at an angle. 
• If a wave is travelling along the normal, it chnae speed but is not refracted.

There are seven types of electromagnetic waves

• Waves with similar wavelengths tend to have similar properties.
• All forms of electromagnetic radiation travel at the same speed through a vacuum.
• Shorter Wavelengths = Higher Frequency.

Radio Waves, Microwaves, Infa Red, Visible Light, Ultra Voilet, X-Rays,Gamma Rays

The properties of EM waves depend of Frequency and Wavelength

• As the frequency and wavelength of EM radiation changes, its interaction with matter changes - the way it's absorbed, reflected or transmitted.
• Waves at each end of the spectrum are able to pass through material whereas in the middle they are absorbed.
• Waves with higher frequency (shorter wavelength) tend to be more dangerous because they have more energy.

Different sorts of signals have different advantages

• EM waves can be used for communication.

Advantages:

• Signals travel really fast.
• Can carry lots of information very quickly.
• Information is secure inside a cable that cannot be tapped into like radio signals.

Disadvantages:

• Cables difficult to repair.
• Not portable like wireless communication.

Communicating with light can require a code

• Historically, light was used to speed up long distance communication.
• The Morse Code is an example. It was a digital signal as the lightpulse is only either "on" or "off".

Light signals can travel through optical fibres

• They can carry data over long distances as pulses of light or infared radiation.
• The waves bounce off the sides of a narrow core which is protected by outer layers.
• The ray of light enters the fibre and hits the boundary at an angle greater than the critical angle for the material, causing total internal reflection of the ray in the core. This repeats until it meets the other end.

Using light has a lot of advantages

• Quick way to communicate. In a vacuum light travels at 300,000,000m/s. It is slowed in a fibre by 30%, but is still fast.
• Multiplexing means that lots of different signals can be transmitted down a single optical fibre at the same time.

Lasers produce narrow, intense beams or monochromatic light

• Ordinary light is a combination of waves of different frequency and wavelength and are "out of phase" with each other.
• A laser beam is a ray of visible light that has a few extra properties which make it special:
• All the waves are at the same frequency, making the light monochromatic (one single, pure colour)
• The light waves are all in phase with each other - the crests and troughs line up - increasing the amplitude.
• Lasers have low divergence. The beam is narrow and stays narrow for long distances.

CD players use lasers to read digital information

• The surface of a CD has a pattern of billions of shallow pits cut into it. The area around these pits are called lands.
• A laser is shone onto the CD and is reflected fromthe shiny bottom surface as it spins.
• The beam is reflected from a land and a pit differently and this can be picked up by a light sensor. These changes can be changed into an electrical signal.
• It's the change in the reflected beam which represents on while no charge represents off, not the pits and lands themselves.
• An amplifier and a loudspeaker convert the signal into sound of the right pitch and loudness.

Infared has many uses around the home

- Cooking, remote Controls, mobile phones and computer comunication ( data transfers ), security Systems, optical fibres (instead of visible light)

IR can be used to monitor temperature

• Infared radiation is also known as heat radiation. It is given out by hot objects. The hotter it is = the more IR given out.
• IR is also detected by night-vision equipment. It is changed to an electrical system and displayed on a screen as a picture.
• The hotter the item, the brighter it appears.

IR signals can control electrical equipment

• Remote controls emit pulses of IR to control electrical devices like TVs or DVD players.
• The pulses act as digital on/off code, similar to Morse Code.
• IR signals are used in the same way to transfer information between mobile ohones and computers over short distances.
• The main drawback is that you need to be close to the device and need to point the beam straight at the detector.

Long wavelengths travel well through Earth's atmosphere.

• Radio waves and microwaves are good at transferring information over long distances. This is because they don't get absorbed by Earth's atmosphere as mycg as waves in the middle or high-frequency end of the spectrum.

Radio waves are used mainly for communications

• Radio waves are EM radiation with wavelengths longer than about 10cm.
• Different wavelengths of radio wave refract and diffract in different ways.
• Long-wave radio waves (1-10kn) can be recieved halfway around the world because they diffract around the curved surface of the Earth.
• Radio waves used for TV and FM radio are short (10cm-10m). To get the signal you must be in direct sight of the transmitter. The signal doens't bend or travel far through buildings.
• Short-wave radio signals (10m-100m) can be recieved at long distances because of reflection in the ionosphere. Depending on atmospheric conditions, the shorter medium-wave signals can also reflect from the ionosphere.

Diffraction makes a difference to signal strength

• Diffraction is when waves spread out at the edges when they pass through a gap or past an object.
• The amount of diffraction depends on the wavelength of the wave relative to the size of the gap or obstacle.
• Longer wavelengths can encounter a lot of diffraction - They are large compared to gap or obstacle.
• This means they are able to bend around corners and obstacles.
• Longer wavelength radio waves can travel long distances between transmitter and reciever without having to be in line of sight.
• Shorter wavelength radio waves and microwaves don't diffract much so transmitters need to be high up and still only cover short distances.

Refraction can help radio waves travel further.

• If the wave hits the new substance at an angle, it changes direction. This is refraction.
• UV radiation from the Sun creates layers of ionised atoms in Earth's atmosphere. These electrically charged layers are called the ionosphere.
• Radio waves travel faster through the ionosphere, causing refraction to occur. 
• Short and meduim wave radio signals are refracted back most in the ionosphere (bounced back or reflected to Earth).
• This means that short and meduim wave signals can be recieved a long way from the transmitter.
• The amount a wave is refracted depends on its frequency and angle of elevation. High frequency/ short wavelenght signals don't refract as much as medium wave,
• Radio waves 'bounce off' the ionosphere in a similar way to how light waves totally internally reflect inside optical fibres.
• Refraction is not always good - it can disrupt the signal by bending away from the reciever dish.

Digital radio helps reduce interference.

• There's a limited number of radio wave frequencies that transmit a good analogue signal.
• Analogue signals often suffer interference because similar wavelengths combine, causing 'noise'. 
• Digital Audio Broadcasting (DAB) works in a diferent way to traditional radio broadcasts. It's digital.
• With DAB many dignals are compressed and transmitted as a single wave - this is called multiplexing.
• They are transmitted across a relatively small frequency bandwidth and seperated out by recievers at other end (if user has a DAB radio set).
• DAB suffers less interference, increasing number of potential radio stations available.
• However, sound quality isn't as good as FM radio broadcast due to compression of signal.

Microwaves are used for satellite communication...

• Microwaves with wavelengths that pass through Earth's watery atmosphere without too much absorbtion occuring are used.
• For satellite TV & phones, signal from transmitter is transmitted into space, is picked up by satellite's reciever dish and is transmitted back to Earth in different direction where it's picked up by a satellite dish on the fround.

... As well as mobile phones.

• Mobile phone calls travel as microwaves from the phone to the nearest transmitter. The transmitters pass signals between each other and back to the mobile phone. 
• Microwaves have a shorter wavelength than radio waves, so they don't diffrct much (affected by curvature of Earth and buildings). This means that transmitters need to be positioned in line of sight (hilltops or high up, close together).

Mobile masts may be dangerous - but there's conflicting evidence.

• Microwaves used in microwave ovens have a different wavelength so they are absorbed by water molecules.
• It's the absorbtion that's harmful. Some people think that the microwaves emitted into your body could damage your health but there is no conclusive proof.

The size of reciever depends on the size of wave.

• The longer the wavelength, the larger the reciever should be.
• Radio waves need the biggest reviever, the microwaves, then infared, then light waves, etc...
• This is because of refraction - when a wave enters a receiver it passes through a gap. If the wave is diffracted, you lose detail. 
• Gaps the same size as the wavelength cause lots of diffraction. The larger the gap, the less diffraction. So the bigger the receiver compaerd with the wavelength, the less diffraction is caused and the information is clearer.

Telescopes detect different types of EM wave.

• Bigger telescopes give us better resolution because they cause less diffraction. 
• Telescopes with smll gaps have linuted resolving power (diffraction-limited).
• To combat this, radio telescopes are often linked together and signals are combined to get more detailed information.

Optical microscopes are diffraction limited.

• They are small for their laboratory use (can't be too big), so it is hard to get a good resolution.

Information is converted into signals.

• To communicate, it needs to be converted into electrical signals before it is transmitted.
• These signals can be sent over long distances as either analogue or digital signals.

Analogue signals vary but digital's just on or off.

• An analogue signal can take any value within a certain range. The amplitude and frequency vary continuously.
• A difital signal can take two values - on/off (1/0 - binary). E.g. optical fibres - pulses of light.

Digital signals have advantages over analogue.

• When you amplify analogue signals, noise is amplified too. This noise is easier to remove with digial so the signal is high quality.
• Multiplexing occurs with digital signals.

Ultraviolet radiationc causes skin cancer.

• UV radiation damages DNA in skin cells. Can also cause eye problems and premature skin aging. SPF is worn to combat this.
• SPF 15 means you can spend 15 times as long in the sun without burning.

The ozone layer protexts us from UV radiation.

• Ozone is made of three oxygen atoms. There is a layer of ozone high in the atmosphere. 
• It absorbs some of the UV rays from the sun, reducing amount of UV radiation reaching Earth's surface.
• Due to use of CFCs, ozone was depleting.

There's a hole in the ozone layer over Antarctica.

• In winter, weather causes concentration of ozone over Antarctica to drop. It increases again in spring, but winter concentration has been dropping. This looks like a 'hole' on satellite images.

Earthquakes cause different types of seismic waves.

When there is an earthquake somewhere, it produces shock waves that travel through the Earth. We record these using seismographs. Scientists measure the time it takes for the shock waves to reach each seismograph. They also note which parts don't recieve the shock wave at all.

P-waves are Longitudinal                                    S-waves are Transverse

P-waves travel through solids and liquids          S-waves only travel through solids.

P-waves are faster than S-waves                       S-waves are slower than P-waves.

The seismograph results tell us what's down there.

• About halfway through Earth, P-waves change direction. This shows a sudden change in properties (mantle to core). S-waves stop at outer core (liquid) and P-waves travel faster through inner core (solid).
• The waves change speed as the properties of the mantle and core change (gradually - curve).