Heat & Temperature
A cup of coffee - 70 degrees celcius - energy stored within the liquid - the energy inside the cup will become the same temperature as the surroundings so the temperature drops.
Iced water - the hot energy outside will move into the cup - the ice will melt.
Thermogram - represents the amount of heat energy is emitted.
White in the thermogram is the hottest.
More heat energy means more kinetic energy which increases the collision frequency.
Specific Heat Capacity
Wooden spoon - warm in soup
Metal spoon - hot in soup
It takes more energy to raise the temperature of the wooden spoon - higher SHC
Specific Latent Heat
The specific latent heat of fusion, l, of a substance is the heat needed to
change a mass of 1 kg the substance from a solid at its melting point into liquid at the same temperature.
The phase change - period of latency - needed to break intermolecular bonds.
Insulating your home
In a house, the heat goes:
- 25% to the roof
- 35% to the walls
- 10% to the windows
- 15% because of draughts
- 15% to the floors
Insulating your home cont.
The payback time of an energy-saving solution is a measure of how cost-effective it is. Here is the equation to calculate payback time:
payback time (years) = cost of installation (£) ÷ savings per year in fuel costs (£)
Radiation & surfaces
A hot cup - you would feel heat coming away from the cup because of radiation - any hot object emits infrared radiation
The hotter the object, the more infrared radiation is emitted
Thermogram - image of how much infrared radiation is emitted by an object
If the object gets hot enough, it may emit light.
The Sun & the Earth - between the two is a vaccuum - radiation doesnt need particles because its an electromagnetic wave
Dull Black surfaces - absorb infrared radiation - thermal energy transferred - temp increased
Shiny silver surface - reflect infrared radiation - less heat transferred - less increase in temp
Conduction & Convection
Frying pan - conduction - supplies heat from beneath the pan through the metal - metal is a good conductor of heat
As the heat increases, the particles collide so heat gets transferred to go through a material - electrons gain heat and is transferred to each other - this quickly increases the temperature
Wooden spoon - poor thermal conductor - good thermal insulator
Metal spoon - good thermal conductor - poor thermal insulator
- Water cools - becomes denser - sinks Conduction - SOLIDS
- Water warms at the bottom - less dense - rises Convection - LIQUIDS & GASES
- Convection current - continous cycle
Energy and efficiency
Light bulb - electrical energy in - 2 types of energy given out - light and thermal - useful energy is the light energy - wasted energy is the thermal energy
Intro to Waves
Intro to Waves cont.
Total Internal Reflection
Angle of incidence
- if the angle of incidence is less than the critical angle, the light refracts away from the normal
- if the angle of incidence is equal to the critical angle, the light refracts at 90 to the normal
- if the angle of incidence is greater than the critical angle - total internal reflection occurs
Lights & Lasers
White light enters prism - spectrum - red light refracted least - blue light refracted most
Morse code - method of communication
Light travels incredibly quickly - useful, SOS messages transfer quickly
dashes and dots only - early digital signals - dot or dash
Lasers - produce narrow beam of light
light from one particular laser is one colour - surgery - dental treatments - CD DVD players
waves - same frequency - inphase - source of coherent monochromatic light - low divergence
CDs - surface has dips - dashes and dots - laser beam shone across the surface - into the dip and internally refelected - signal there can be decoded. Blu ray - more dips - better definition more data
Cooking with waves
Conventional oven - infrared radiation - filament set on fire - when the door is closed, air inside the oven gets hotter, less dense rises. cooler air sinks. over time foods get hotter and hotter.
if food at the top - air touches surface of food - particles vibrate gain kinetic energy. black - good at radiating heat - silver foil relfects infrared to speed up cooking
Microwaves - 1cm into food - high energy - penatrate into food - fat or water
mircrowaves absored by fat or water molecuels - conductions occurs - cooks food from inside outside. white microwave so microwaves reflected into the microwave oven - cooking process quicker
microwaves can pass through glass and plastic - microwave door - thin lines of metal mesh - absorbs microwaves and stops causing you to burn.
mobile phones - converting sound into microwave signal - sends to nearest phone and they can listen to you and talk to you
Transmitter sends out signal - cannot send a signal due to obstructions - buildings, hills
weather - rainy day - less bars of reception - microwaves are absorbed by water therefore reduced signal
the younger you are - thinner the skull - microwaves can go into your brain and it can affect it
younger children - 5 and 13 years - not to use mobiles as frequently as adults - water in the brain, absorb microwaves - potentially cause problems to the brain
curvature of the earth blocks line of sight. satellites used - one station - satellite - 2nd station
live broadcast - delay - has to be transferred to space and back into Earth
Ionosphere - layer of atmosphere - reflect and refract radio waves - lose signal quality - interference -signal muffled and quality of sound in a phone call affected severely
Advantage - no wires needed - sends signal directly to laptop, computer, phone etc
portable and convenient - use on the move - allows access where we couldnt before
Disadvantages - difficulties with reaching it in different parts of the house - more walls - lower signal quality