ENERGY RESOURCES AND ENERGY TRANSFERS Flashcards

Question

Convection?

Answer 1

-transferring thermal energy through a fluid (liquid or gas) when particles in a warmer region gain energy and move into cooler regions, carrying this thermal energy with them -Warm fluids rise up because they are less dense than cooler fluids -Convection currents are set up -In this way the thermal energy is transferred throughout the fluid. -Convection cannot take place in solids because the particles are not free to move to flow elsewhere.

Answer 2

- Heating water in a saucepan users convection (conduction causes the thermal energy to be transferred through the metal base initially). - Air movement, such as winds and breezes is due to warm air rising and cool air sinking, due to changing densities. - Convection heats up rooms and it explains why central heating hot water tanks are higher up in a house, as hot water rises!

Answer 3

* They become less dense! * When the particles of the fluid gain energy they move apart more and the fluid expands. * There are now less particles in the same volume – meaning the fluid has becomes less dense and rises. * Away from the heat source the particles lose energy and the fluid contracts. This makes it more dense, so the fluid sinks. This sets up a convection current in the fluid which repeats the process of energy transfer.

Answer 4

- The difference in the rate of thermal energy transfer by conduction in metals can be demonstrated in many ways. Copper is the best conductor, followed by aluminum, brass and iron/steel. - Non-metals are very poor! - Using dyes or potassium permanganate crystals to colour the clear water can show convection currents in liquid.

Answer 5

- Thermal energy can be transferred by a type of electro-magnetic radiation called Infrared (IR) Radiation - All objects emit and absorb infrared (thermal) radiation - No medium is needed to transfer this energy through (such as with conduction and convection) – it can travel through the vacuum of space, in straight lines at the speed of light (i.e. from the Sun) - You can’t see this thermal radiation but you can feel and sense it!

Answer 6

* Infrared has no colour, but a computer can put a false colour on the special thermal camera images so we can ‘see’ the object. * The colours are put on a scale which corresponds to temperature. White, yellow and red usually represent the warmest areas; green, blue and black usually represent the coolest. These are called THERMOGRAMS

Answer 7

* All objects emit (give out) and absorb infrared (take in) infrared radiation * Hotter objects emit more infrared radiation than a cooler one. * An object that is hotter than its surroundings emits more radiation than it absorbs (as it cools down). * An object that is cooler than its surroundings absorbs more radiation than it emits (as it warms up). * The bigger the difference in temperature between an object and its surroundings, the faster the thermal energy is transferred

Answer 8

MORE infrared radiation

Answer 9

LESS infrared radiation

Answer 10

MORE infrared radiation

Answer 11

- LESS infrared radiation | - they also tend to reflect more too

Answer 12

- Yes - Cold surfaces will absorb more IR from the warmer surroundings, but a dark, dull surface will absorb more than a shiny, light surface

Answer 13

- Yes - Hot surfaces will emit more IR to the cooler surroundings, but a dark, dull surface will emit more than a shiny, light surface

Answer 14

• A Leslie cube will show how different surfaces at the same temperature emit different amounts of radiation. From highest to lowest sensor temperature: 1. Dull Black 2. Shiny Black 3. Dull White 4. Shiny White • Plotting a cooling curve from two cans of hot water shows the black surface emits radiation quicker

Answer 15

LIQUIDS AND GASES

Answer 16

HEAT WAVES

Answer 17

* Some materials are very poor conductors of heat. These are called thermal insulators. * Examples of materials that are insulators include plastics, wood, ceramics and air. * Air becomes a very effective insulator when it is trapped and stopped from moving and taking energy away. * This is how your clothes keep you warm – air is trapped between the fibres and so acts as an insulator. * Other insulating materials, including polystyrene and loft insulation, use trapped air because it is so effective. * Poor house insulation loses energy, costs more and means more CO2 is produced when generating energy.

Answer 18

- roof =20% - windows =12% - doors = 4% - floor 28% - walls 36% - home insulation can reduce these losses

Answer 19

1. Windows – Double glazing reduces conduction 2. Doors – Draught excluders reduces convection 3. Walls – Cavity walls with foam insulation - reduces conduction and stops convection in between 4. Floors – Carpets – reduces conduction 5. Roof – Loft insulation – reduces conduction -Insulators are poor conductors of thermal energy and reduce energy transfer by heating. -Use of white or shiny surfaces can reduce heat loss by radiation

Answer 20

• When an object is moved by a force, energy is transferred to it and its energy store is increased. • Moving an object increases its kinetic energy store • Lifting an object increases its gravitational potential energy store • Stretching or squashing an object increases its elastic potential energy store • In Physics, we say WORK is DONE on the object.

Answer 21

- work done (W) = force (F) x distance moved (d) - W=Fd - W= work done (J) - F= force (N) - D= distance moved (m) -F=W/d OR d=W/F

Answer 22

• When you push an object across a surface, there is an opposing force of friction resisting you. • You need to do extra work to overcome this friction! • Multiply the friction force (N) by the distance moved (m) and you can calculate the work done against friction (J). • Work is done against air resistance (air friction) as well • Work done against friction is mainly transferred to thermal energy stores by heating and then dissipates to the surroundings

Answer 23

• When you lift up an object, work is done (energy is transferred). • It gains gravitational potential energy. • Remember when you use a force (F) to move an object a distance (s), the work done (energy transferred) W = Fd • The force you need to apply is equal to the weight of the object (mg) and distance moved is the height change (h). • The more weight you lift, the more energy you transfer. • The greater the height change, the more energy you transfer. • Energy transferred (vertically) = weight x height change

Answer 24

- GPE (GPE) = mass (m) x gravitational field strength (g) x height (h) - GPE = mgh - GPE = gravitational potential energy (J) - m = mass (kg) - g = gravitational field strength (N/kg) - h = height change (m) -This can be rearranged to give: m = GPE/gh OR h = GPE/mg OR g = GPE/mh

Answer 25

* Kinetic energy is an object’s energy store due to it moving. * All moving objects have kinetic energy, but the amount of kinetic energy they have depends on how fast they are moving (speed or velocity) and the mass they have. * The more speed it moves with, the more kinetic energy it has. * The more mass it has, the more kinetic energy it has.

Answer 26

-Kinetic Energy (KE) = 1⁄2 x mass (m) x speed2 (v2) KE = 1⁄2mv2 - KE = kinetic energy (J) - m = mass (kg) - v = speed (or velocity) (m/s) -You can write 1⁄2 as 0.5 if you wish. -This can be rearranged to give: m = 2KE/v2 or v = √(2KE/m

Answer 27

• Kinetic energy (KE) and gravitational potential energy (GPE) can transfer between each other. • Given the assumption that no energy is lost, then when an object is dropped from a height, it loses GPE, but gains KE • Throw an object into the air and it loses KE, but gains GPE CHANGE IN GPE = CHANGE IN KE mgh = 1⁄2mv2 • We see this changing of energy stores all the time – with from rockets, roller coasters, pendulums, airplanes etc.

Answer 28

• Two people (or machines) may transfer the same amount of energy (or work done) – in joules (J), but one of them may have done this quicker! • The rate of work done (or energy transfer) is called POWER • The tortoise and the hare might travel the same distance – but the hare will do it in less time, so is more powerful! • Power can be shown in joules/second (J/s), but it also has its own unit called the watt (W)

Answer 29

- power (P) = work done (W) ÷ time taken (t) - P = W/t - Power is measured in watts (W) = joules/second (J/s) - P = power (W) - W = Work done (energy transferred) (J) - t = time taken (s) -This can be rearranged to give: W = Pt and t = W/P

ENERGY RESOURCES AND ENERGY TRANSFERS Flashcards

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