Energy Transfer by heating

Description

Physics
oliviabaines
Flashcards by oliviabaines, updated more than 1 year ago
oliviabaines
Created by oliviabaines over 10 years ago
317
4

Resource summary

Question Answer
Infrared Radiation(heat) -Electromagnetic spectrum, beyond visible red light -Emitted by all objects -Can travel through a vacuum -The hotter an object, the more radiation it emits in a given time
-Dark, matt surfaces are good absorbers and emitters of IR. Transfer energy and cool down quickly -Light, Shiny surfaces are good reflectors of IR States of matter -Solid, liquid, gas.Change them by heating and cooling
Solid -Fixed Shape -Transfers energy by vibrating -Good conductors(metals) Liquid -Can flow -No fixed shape -Particles in contact but can move about at random -Poor conductors
Gas -Particles are far apart, move at random, much faster -No fixed shape and can flow -Less dense
Conduction -One end of a solid is heated, the particles at the end gain kinetic energy and vibrate more -Energy is passed to neighbouring particles helped by free electrons colliding amongst the atoms -Occurs in metals Insulators -Poor conductors -Wool and fibreglass are good insulators as they contain trapped air
Convection -occurs in fluids -When a fluid is heated it expands -Becomes less dense and rises -Warm fluid replaced by cooler, denser fluid -The resulting convection current transfers energy throughout the fluid
Evapouration -Liquid turns into a gas -The most energetic liquid moleculesescpae from the surface and enter the air; the average kinetic energy of the remaining molecules is less so the temp. of the liquid decreases -So evapouration causes cooling Rate of evapouration increased by: -increasing the surface area of the liquid -increasing the temp. of the liquid -creating a draught of air across the liquid's surface
Condensation -Gas turns into a liquid -Takes place on cold surfaces(mirrors) Rate of condensation increased by: -increasing the surface area -Reducing the surface temp.
The greater the temp. difference between an object and its surroundings, the greater the rate at which energy is transferred This depends on: -the materials the object is in contact with -the object's shape -the object's surface area
Sometimes we want to maximise the rate of energy transfer to keep things cool -we use things that are good conductors -dull black -the air flow around them maximised Sometimes we want to minimise the rate of energy transfer of energy by conduction, convection and radiation - we use things that are good insulators -white and shiny -prevent convection currents by trapping air in small pockets
Motorcycle Engine Fins -Has many small fins to provide a large surface area so it keeps the engine cool and does not overheat - Releases heat quickly
Vacuum flask -stucture minimises energy transfer by conduction, convection and radiation -reduces the rate of energy transferto keep hot things hot and cold things cold
Specific Heat Capacity -amount of energy required to raise the temp of 1 kilogram of the substance by 1 degree c -The greater the shc, the more energy required for each degree temp. change -The greater the mass of substance being heated the more energy required for each degree temp. change
Energy transferred=Mass x shc x temp. change E=m x c x 0 Heating and insuating buildings -The rate of energy transfer to or from our homes can be reduced fibreglass loft: stops conduction Cavity wall: traps air in small pockets reduces convection Double glazing: reduces conduction through windows Draught proofing: reduces convection Aluminium foil behind radiators: reflect IR back into the room
U-Value -how much energy per second passes through different materials; allows us to compare them -The lower the u-value the better the material is as an insulator Solar heating panels -contain water heated by radiation from the sun -used to heat buildings/hot water -Cheap to run as they don't use fuel -expensive to buy and install -water not heated at night
Forms of energy -Light, sound, kinetic(movement), nuclear, electrical, gravitational potential, elastic potential and chemical -last three are forms of stored energy -Energy can be transferred from one form to the other -Any object above the ground has gravitational potential energy -A falling object transfers gravitational potential energy to kinetic energy
Conservation of energy -law stating it is not possible to create or destroy energy. It is only possible to transfer it from one form to another, or from one place to another -Total amount of energy is always the same. Applies to all energy transfers E.g. when an object falls, gravitational potential energy is transferred to kinetic energy -stretching an elastic band transfers chemical energy to elastic potential energy -In a solar cell, light energy to electrical energy
-A machine is something that transfers energy from one place to the other or from one from to another. The energy produced by the machine consists of: useful energy- energy in the place we want it and the form we need it wasted energy- energy not usefully transferred Useful energy and wasted energy both end up being transferred to the surroundings, which become warmer -As energy spreads out, it gets more and more difficult to use for further energy transfers -Energy is often wasted because of friction between moving parts of a machine
Energy(J) and Efficiency -Energy supplied is the input energy. From the conservation of energy we know: input energy= useful energy transferred+energy wasted The less energy that is wasted by a machine, the more efficient it is Efficiency=useful energy x 100 total energy
No appliance can be 100% efficient, except an electric heater, which usefully transfers all of the electrical energy supplied to it by heating its surroundings -Energy transfer through an appliance can be represented with a Sankey diagram
Electrical appliances -transfer electrical energy into whatever form of energy we need at the flick of a switch -lamps(light), speakers(sound),tv(light and sound) often transfer energy by heating -Appliances should be designed to waste as little energy as possible
Electrical Power -the power of an appliance is the rate at which it transfers energy -1 watt transfers 1 joule every second 1kilowatt=1000 watts Power= energy time taken(s) for energy to be transferred -Power is the energy per second transferred or supplied, so we can write the efficiency equation in terms of power
Using electrical energy -A kwh is the amount of energy transferred by a one-kw appliance when used for one hour Amount of energy transferred E= power x time taken -The electricity meter in a house records the number of kwh of energy used. If previous meter reading is subtracted from the current reading= the electrical energy used between the readings
The cost of the electrical energy total cost=number of kWh x cost per kWh -the cost per kWh is given on the electricity bill Comparing Cost effectiveness of appliances includes: -cost of buying the appliance -the cost of installing the appliance -the running costs -the maintenance costs -environmental costs -the interest charged on a loan to buy the appliance
To reduce energy bills many may buy newer, more efficient appliances, or install materials designed to reduce energy wastage -the payback time is the time it takes for an appliance or installation to pay for itself in terms of energy savings
Show full summary Hide full summary

Similar

AQA Physics P1 Quiz
Bella Statham
Physics P1
themomentisover
Weimar Revision
Tom Mitchell
Biology Revision - Y10 Mock
Tom Mitchell
Hitler and the Nazi Party (1919-23)
Adam Collinge
History of Medicine: Ancient Ideas
James McConnell
Geography Coastal Zones Flashcards
Zakiya Tabassum
Biology- Genes and Variation
Laura Perry
FREQUENCY TABLES: MODE, MEDIAN AND MEAN
Elliot O'Leary
CUMULATIVE FREQUENCY DIAGRAMS
Elliot O'Leary
Enzymes and Respiration
I Turner