Zusammenfassung der Ressource
P1
- Heating Houses
- Energy flow
- Energy flows from a warmer to a colder
body. When energy flows away from a
warm object, the temperature
decreases
- Measuring
temperature
- A thermogram uses colour to
show temperature; hottest:
white/yellow coldest:black/dark
blue/purple.
- Temperature is a
measurement of hotness on
a arbitary scale.
- When the
temperature of a
body increases, the
average kinetic
energy of the
particles increases
- Heat is a measurement of internal
energy, it is measured on an absolute
scale.
- Specific heat capacity
- Energy needed to raise the
temperature of 1kg by 1
degree c
- Measured in Joules
per kg degree celsius
j/kgoc
- energy transferred
= mass x specific
heat capacity x
temperature change
- Specific latent heat
- Energy needed to melt or boil 1kg
of the material
- Measured in Joules
per kilogram J/kg
- energy transferred = mass x specific
latent heat
- When a substance changes state,
energy is need to break the bonds that
hold the molecules together. This
explains why there's no change in
temperature.
- Keeping homes warm
- Practical insulation
- Double Glazing - Reduces
energy loss by conduction. Gap
between 2 pieces if filled with
gas/contains a vaccum.
Particles in a gas are far apart,
it's very difficult to transfer
energy
- Loft insulation - reduces energy
loss by conduction and convection.
- Warm air rises - Energy is
transferred through ceiling by
conduction - Air in loft is warmed
and trapped by insulation, both
sides are same temp so no energy
is transferred
- Cavity wall- reduces energy
loss by conduction and
convection. Air in foam is good
insulator, and the air can't
move because it's caught in
the foam
- Insulation blocks- used to build new
homes, shiny foil on both sides to reduce
radiation; - energy from sun is reflected to
keep the home cool in summer, energy
from home is reflected back to keep
home warm in winter
- Conduction, convection and radiation
- Conduction - due to the transfer of kinetic
energy between particles
- Convection - Gas expands when it's
heated. Less dense, so rises.
Density = kg/m3
- Density = mass / volume
- Radiation doe not need a material to transfer
energy. Energy can be transferred through a
vaccum
- Energy efficiency
- efficiency = useful energy output (x100%) / total energy
input
- Energy from home is lost to the environment
- Different types of insulation cost
different amounts and save
different amounts of energy
- Payback time = cost of insulation
/annual saving
- Buildings that are
energy efficient are well
insulated; little energy is
lost to the surroundings
- Designers and
architects have to make
sure that little energy is
lost
- Spectrum of waves
- Wave properties
- Amplitude - Maximum displacement
of a particle from its rest position
- Crest - Highest point
- Trough - Lowest
point
- Wavelength - distance between
two successive points having
same displacement
- Frequency - Number of complete
waves passing a point in one second
- wave speed - frequency x wavelength
- Getting messages across
- Some optical instruments
such as periscope use
two or more plane mirrors
- Refraction occurs because
speed of waves decreases
as wave enters a more
dense medium and
increases as the wave
enters a less dense
medium. Freq stays same
but wavelength changes
- Diffraction is the
spreading out of a wave
as it passes through a gap
- Amount of diffraction depends on
size of gap; the most diffraction
occurs when the gap is a similar
size to wavelengths. Effects are
noticeable in telescopes and
microscopes
- Size of communications
receiver depends on
wavelength of radiation
- Light and lasers
- Morse code
- Uses a series of dots and
dashes to represent the
alphabet. Used by signalling
lamps as series of short and
long flashes of light. Example
of digital signal
- Sending signals
- When sent by light, electricity,
microwaves or radio, almost
instantaneous
- Advantages and
disadvantages. Can the
signal be seen by others?
Can the wire be cut? How
far does the signal have
to travel?
- Laser light
- White light is made up
of different colours of
different freq. out of
phase
- Has only a single
frequency, is in phase and
shows low divergence
- Used to read from the surface of a
CD. As pitted, which represents
digital signal, laser light is shone
onto cd surface and reflection
provides info for digital signal
- Critical angle
- Normally refraction happens
when light travels from one
material to another
- If it's passing from a more
dense material into less dense,
the angle of refraction is lager
than the angel of incidence
- When angle is 90 degrees, the
angel of incidence is called the
critical angle
- Total internal
reflection - when
the angle of
incidence is
bigger than the
critical angle
- Some fibres are coated to improve reflection
- Endoscopy
- Allows doctors to see inside a body
without the need for surgery. Light
passes along one set of optical fibres to
illuminate inside of the body, the light is
reflected and then passes up another
set of fibres to the eye/camera
- Cooking and
communicating
using waves
- Cooking with waves
- Infrared radiation doesn't
penetrate food easily
- Microwaves penetrate
up to 1cm into food
- Microwaves can penetrate glass
or plastic but are reflected by
shiny metal surfaces. Special
glass in a microwave open door
reflects them and they can cause
body tissue to burn
- Electromagnetic spectrum
- Energy is transferred by waves; the
amount of energy depends on the
frequency or wavelength of the wave
- High frequency (short wavelength)
waves transfer more energy
- Ovens cook food by infrared radiation;
energy is absorbed by the surface of food,
the kinetic energy of the surface increases,
the rest of the food is heated by
conduction
- Microwave ovens cook by
microwave radiation- the water/fat
molecules in the outer layers of food
vibrate more
- Microwaves
- Microwaves have
wavelengths between
1mm and 30cm
- Phones use longer wavelengths than microwave
ovens, less energy is transferred
- Microwave radiation is used to communicate over long distances. The transmitter
and receiver must be in line of sight.
- Satellites are used for microwave communication. Signal
from Earth is received, amplified and re-transmitted back to
Earth. They're in line of sight because there are no
obstructions in space.
- Microwaves do not show much
diffraction, adverse weather and large
areas of water can scatter the
signals, the curvature of the Earth
limits the line of sight so transmitters
have to be on high buildings.
- Mobile phones can interfere with sensitive
equipment -this is why they are banned on
planes and in hospitals.
- Wireless signals
- Radio refraction and
interference
- Wireless technology is used by
radio and television, laptops,
mobile phones
- Radio waves are reflected and refracted in the Earth's
atmosphere: the amount of refraction depends on the
frequency of the wave/there is less refraction at higher
frequencies
- Radio stations
broadcast signals
with a particular
frequency
- The same frequency can be used by
more than one radio station; the radio
stations are too far away from each other
to interfere/but in unusual weather
conditions, the radio waves can travel
further and broadcasts interfere
- Digital Audio Broadcasting or DAB
also provides a greater choice of
radio stations but the audio quality
isn't as good as the FM signals. DAB
eliminates interference between
other radio stations
- Radio reflection
- Radio waves are reflected in
the ionosphere. They behave
like light in an optical fibre and
undergo total internal reflection
- Water reflects radio waves but
land mass doesn't
- Continued reflection by the
ionosphere and the oceans allows
radio waves to be received from an
aerial that is not in line of sight
- Microwaves
pass
through the
ionosphere
- Microwave signals are
received by orbiting satellites,
amplified and retransmitted
back to Earth
- Communication satellites orbit
above the equator and take 24
hours to orbit Earth
- Communication problems
- Radio waves are diffracted when they
meet an obstruction
- Refraction in the atmosphere needs to be
thought about when sending a signal to a
satellite
- Transmitting aerial needs to send a focused beam to
the satellite - aerial is small
- Transmitted beam is slightly divergent
- Some energy lost from edge because of diffraction
- Stable Earth
- Earthquake waves
- A seismograph
shows the
different types of
earthquake wave
- L waves travel around the surface VERY slowly
- P waves are longitudinal pressure waves: P waves travel
through the Earth between 5km/s and 8km/s
- Can pass through solids and liquids
- S waves are transverse waves. They travel through the
Earth at between 3 km/s and 5.5 km/s/
- Can only pass through solids
- Earth's insides
- P waves travel through the Earth and are refracted by the core
- The paths that are taken by P waves help scientists figure out how big the Earth's core is
- S waves are not detected on the opposite
side of the Earth to an Earthquake. They can't
travel through liquid, which means that it tells
the scientists that the core is liquid
- Tan or burn
- Tan- caused by the action
of ultraviolet light on the
skin
- Cells in the skin produce melanin, a pigment
which produces a tan
- People with darker skin don't tan as easily
because uv radiation is filtered out
- maximum time to spend in the sun = published
normal burn time x SPF
- People are becoming more aware of the
dangers- like sunbeds
- Ozone depletion
- Scientists didn't believe that there was a thinning
of the ozone layer, they thought the instruments
were faulty but they compared with others and
were confident in their findings
- Ozone is found in stratosphere
- Helps filter out UV radiation
- CFC gases (aerosols) destroy the
ozone and thin it out. This increases
danger to us
- Agreement to reduce CFC emissions
- The ozone layer is at its thinnest above the
South Pole because the chemicals work best in
cold conditions
- Scientists monitor the thickness by using satellities