OCR Physics Module P1 ENERGY FOR THE HOME
P1a Heating Houses
Temperature
Heat
Energy flow
Thermogram
Energy – to change temperature
Specific heat capacity
Specific heat capacity – equation
Melting/freezing/boiling
Specific latent heat
Specific latent heat – equation
Specific latent heat – energy
measurement of hotness (˚C); measure on chosen scale
measurement of energy (J); on absolute scale
energy flows from a hot body to a cooler one; hotter bodies cool; cooler bodies warm
temperature can be represented by a range of colours in a thermogram
depends on mass; material made from; temperature change
how much energy can be held; energy to raise temperature of 1kg by 1˚C; different for different materials
energy (J) = mass X specific heat capacity x temperature change.
change of state; energy transferred but no temperature change
energy is needed to melt or boil; energy needed to melt or boil 1kg; different for different materials/states
energy (J) = mass X specific latent heat
used to break inter-molecular bonds and this explains why temperature does not change
P1b Keeping homes warm
Energy saving methods
Energy saving methods – explain
Conduction
Convection
Radiation
Savings – cost/data
Efficiency
double glazing, fibreglass/mineral wool (loft); foam (cavity wall); curtains; draft excluders; reflective foil
in terms of conduction, convection and radiation
foams/ loft insulation contains air – poor conductor; glass – poor conductor
foam traps air – stops movement/convection; draft proofing stops air moving
reflective foil on or in walls
calculate pay back time
efficiency = useful energy output ÷ total energy input
P1c How insulation works
Conduction
Convection
Convection – wall cavity
Radiation
air in a material is a very good insulator; of KE between particles
hot air rises and is replaced by falling colder air; change of density causes (bulk) fluid flow
unless air is trapped in foam, there will still be energy loss by convection in a cavity wall
infrared energy can be reflected from a shiny surface; infrared radiation needs no medium
P1d Cooking with waves
Electromagnetic spectrum
Emission of radiation
Absorption of infrared
Infrared
Microwave oven
Microwaves
Microwaves – energy transfer
Infrared – energy transfer
Dangers
Mobile phones
Mobile phones – concerns
Microwaves – communication
Microwaves – signal loss
P1e Infrared signals
Infrared radiation
Infrared sensors
Signal types
Digital signals – advantages
Gamma; X-rays; Ultra-violet; Visible light; Infra-red; Micro; Radio
hotter objects emit more radiation; black dull objects emit more radiation
radiation is absorbed by surface of an object, increases temperature black surfaces – good absorbers
heats the surface of the food; reflected by shiny surfaces
microwaves cause heating when absorbed by water
penetrate (about 1cm) into food; reflected by metal; cause burns when absorbed by body tissue;
go through glass and plastics
absorbed by water in outside layers increasing their KE; energy to centre of food – conduction/convection
absorbed by all particles on the surface increasing their KE; energy to centre of food – conduction/convection
energy associated with microwaves and infrared depend on their frequency and so potential danger
use microwave signals
children using mobile phones; residents near to the site of a mast
used to transmit information over large distances that are in ‘line of sight’; some areas/places have poor signals
caused by diffraction/interference of microwaves; limited distance between transmitters; high positioning of
transmitters; nuisance of obstacles affecting signals
Optical fibres
Optical fibres – transmission
Critical angle
remote controls (TV, video, DVD,) automatic doors; short distance data links (computer or mobile phones)
detect body heat and are used for: burglar alarms; security lights
analogue (continuously variable value); digital (either on (1) or off (0)
more information transmitted because of multiplexing (interleaving of many digital signals on the same data line);
less interference (noise not recognised and amplified)
Total Internal Reflection (TIR); happens at glass-air, water-air or perspex-air boundary; reflection of light/infrared
rapid transmission of data; allow the transmission of data pulses using light
light reflected internally through fibre when incident angle greater then critical angle
P1f Wireless signals
Wireless technology
Advantages
Reflection of radio waves
Radio interference
Communications – refraction
Communications – diffraction
Digital signals – advantage
radio; mobile phones; laptop computers
available 24 hours a day; no wiring needed; portable and convenient
long-distance communication – reflection of waves from Ionosphere or received and re-transmitted from satellites
radio stations with similar transmission frequencies often interfere
at the interfaces of different layers of Earth’s atmosphere causes signal loss
by transmission dishes results in signal loss
lack of interference
P1g Light
Transverse waves
Transverse waves – features
Wave equation
Electromagnetic waves – speed
Morse code
Laser
CD player
disturbance/vibrations at right angle to direction of travel
identify trough; crest; amplitude; wavelength; frequency (waves per second; Hertz, Hz)
wave speed = frequency X wavelength
em waves travel at 300, 000, 000 m/s in space (vacuum)
light used to send signals
produces an intense beam of light in which all the waves: have same frequency; in phase with each other
laser beam used – reflection from shiny surface: surface contains digital information – patterns of pits
P1h Stable Earth
Earthquake shock waves
P-waves
S-waves
P/S waves – evidence of internal
Ultraviolet radiation
Darker skins
Sun block
Sun exposure time – calculation
Ozone layer
Global warming
Weather patterns – dust
Weather patterns – dust
seismic waves; travel inside the Earth; cause damage; detected by seismometers; evidence of internal structure
longitudinal; travel through both solids and liquids and travel faster than S-waves
transverse; travel through solids but not through liquids
P-waves through solid and liquid rock (all layers of Earth); S-waves cannot go through liquid rock (outer core)
causes suntan; sunburn; skin cancer
reduce cancer risk; absorb more UV; let less ultraviolet radiation reach underlying body tissues
SPF = sun protection factor; high factors reduce risks more/allow longer exposure without burning
e.g. SPF of 15 means you can spend 15 times as long you spend in sun without burning
ozone layer protects Earth from UV radiation and that environmental pollution from CFCs is depleting the layer
increased energy use; increased CO2; deforestation; causes climate change
from natural phenomena; dust from volcanoes reflect radiation from the Sun causing cooling
from human activity; dust from factories reflect radiation from the city causing warming