Heat Transfer

Question 1

what are thermometers used for

Answer 1

to measure the temperature which depends on how much the particles are vibrating

Question 2

what is internal energy

Answer 2

the total amount of heat energy in an object

Question 3

what is the difference between heat and temperature

Answer 3

hear is the total internal energy in a substance temperature is how much the particles are vibrating

Question 4

how many kelvin is 0 degrees

Answer 4

273K

Question 5

how many degrees is absolute zero

Answer 5

-273 degrees

Question 6

explain expansion

Answer 6

when materials are heated it causes the particles to move more (in metals they vibrate more and with liquids they move faster) due to the energy from the heat. They take up more space from the particles moving causing the material to expand

Question 7

explain conduction in metals

Answer 7

in metals there are lots of free electrons. these electrons move about at random in the metal and hold the positive ions together. When the metal is heated in one area, the free electrons in that area gain more kinetic energy and move faster. These electrons diffuse and collide with other free electrons and ions in the cooler parts of the metal. As a result, kinetic energy is transferred to these electrons and ions causing the heat to travel.

Question 8

why are metals better conductors than non-metals

Answer 8

in a solid that isn’t metal, every can only be transferred through vibrations of the atoms that shake each other. This is much less effective than using free electrons in metals.

Question 9

what are insulators

Answer 9

materials that don’t conduct heat

Question 10

explain how convection works

Answer 10

convection only occurs in fluids (gas and liquids) and is due to convection currents in the fluids. the currents are caused by the fluids rising when they are heated (they become less dense) and then the fluids sink when they cool down (they become more dense). Convection currents transfer thermal energy from the hotter parts to the cooler parts.

Question 11

why do fluids rise when heated

Answer 11

the fluids expand when heated, this means that the particles move about more and take up more space. This causes the density to decrease because the same mass of fluid occupies a bigger volume. so if you heat part of a fluid it will rise.

Question 12

explain thermal radiation

Answer 12

every object emits thermal radiation, the hotter an object is, the more it emits. Thermal radiation can also be called infra-red radiation because it is beyond the red part in the visible spectrum. we can’t see the infrared rays so we can use special cameras to see objects in the dark from their thermal radiation. the sun emits solar radiation

Question 13

what surfaces are the best emitters of radiation

Answer 13

dark matt surfaces emit the most radiation while light shiny surfaces emit the least. this is because when radiation hits matt surfaces the infrared ray will be scattered and absorbed while on a shiny surface it is just reflected and absorbed

Question 14

what surfaces absorb radiation better

Answer 14

dark matt surfaces absorbs radiation better than light shiny surfaces because the cavities in the matt surface trap and absorb the radiation

Question 15

if you had two beakers filled with the same amount of water but one had a black matt surface and one had a shiny light surface which would warm up quicker and why

Answer 15

the black matt one because the cavities in the surface would trap and absorb the radiation while the shiny surface would reflect it

Question 16

what sort of blanket would be best to stop someone from getting cold

Answer 16

a light and shiny blanket as it emits the least radiation

Question 17

why are car radiators painted black

Answer 17

because black emits the most heat, so when thermal energy is transferred from the car engine the radiator can quickly emit it so the engine doesn’t get too hot

Question 18

what happens to the rate of heat transfer from a car engine to a radiator when the cooling fan is switched on

Answer 18

the rate of heat transfer speeds up. This is because when it isn’t switched on the air around the heater warms up but doesn’t move away, making the whole area around the radiator a similar temperature. When the cooling fan is switched on it moves the air away so the temperature gradient remains the same.

Question 19

explain how the vacuumflask keeps the drink at the same temperature

Answer 19

• the vacuum prevents conduction and convection between walls
• the plastic cap is a good insulator
• the glass surface is silvered to stop emitting radiation
• the glass is a bad conductor so there isnt good conduction through the glass
• the insulated support is an insulator

Question 20

why is cavity walls insulation better than just air

Answer 20

while air is a good insulator, if you have large spaces of it then convection currents could be formed. Cavity walls trap the air in a space between them and reduces heat loss, it is filled with insulation to stop heat leaving the house. and there are two other layers of insulation

Question 21

what is evaporation

Answer 21

evaporation is when particles leave the surface of a liquid using their kinetic energy, it happens more with hot liquids beacuse there is more energy but can happen at any temperature. The particles that leave the surface have more energy that other particles and when they leave the average energy will decrease but evaporation will still occur

Question 22

why does a bimetallic strip curve when it’s heated

Answer 22

It curves because one of the sides will have a faster rate of expansion when it’s heated. Because they are bonded the only way for one of the strips to expand faster than the other one will cause the strips to curve.