chapter 13- energy transfer by heating

Question 1

what material is the best conductor

Answer 1

metal

Question 2

what materials are the best insulators

Answer 2

wool and fibreglass

Question 3

why are non metals poor conductors

Answer 3

does not contain free electrons

Question 4

conduction in metals

Answer 4

-free electrons transferring energy inside a metal

Question 5

what happens if you heat a metal rod at one end

Answer 5

the free electrons at the hot end gain kinetic energy and move faster, these elestrons diffuse and collide with other free electrons and ions in the cooler part of the metal.

Question 6

what is convection

Answer 6

circulation of a fluid (liquid or gas) caused by heating it, only occurs in liquids and gases

Question 7

why do fluids rise when heated

Answer 7

-the particles move around and move apart, taking up more space, thus the density of the fluid decreases, bceause the same mass of the fluid now occupies a much bigger volume, as the fluid cools it becomes more dense and sinks

Question 8

evaporation

Answer 8

happens when a liquid turns to gas below its boiling point

Question 9

cooling of a liquid by evaporation…

Answer 9

is caused by faster moving particles escaping from the liquid
-the faster particles have more kinetic energy break away from the attraction of the other particles at the surface and escape the liquid
-after they leave the liquid is cooler because the average kinetic energy of the particles left has decreased

Question 10

factors affecting the rate of evaporation

Answer 10

-increasing the liquid surface area
-increasing the temperature of the liquid
-creating a draught of air across the liquids surface

Question 11

factors affecting the rate of condensation

Answer 11

-increasing the surface area
-reducing the surface temperature

Question 12

the hotter an object is…

Answer 12

the more infared radiation it emits in a given time

Question 13

the greenhouse effect

Answer 13

-earths atmosphere acts like a green house
-short wavelength infrared radiation from the sun can pass through glass and warm the objects inside the greenhouse
-infrared radiation from these warm objects is trapped inside the glass because the objects emit infrared radiation of longer wavelengths that cant pass through the glass

Question 14

what surfacses absorb more infrared radiation than light,shiny surfaces

Answer 14

dark, matt surfaces

Question 15

what surfaces reflect more infrared radiation than dark, matt surfaces

Answer 15

light, shiny surfaces

Question 16

why cant dark, matt surfaces reflect much infrared radiation but absorb it

Answer 16

because matt surfaces has lots of cavities and imperfections

Question 17

the rate of energy transfer to or from and object depends on?

Answer 17

-the shape, size and type of material
-the nature of the surface that the object is in contact with
-the temperature difference between the object and its surroundings

Question 18

the vacuum flask

Answer 18

• the vacuum between the 2 walls of the container prevents energy transfer by convection or conduction betwene the walls
  -glass is a poor conductor
  -glass surface is silvered to reduce radiation from the outer wall
  -the spring supporting the double walled container is made of plastic, good insulator
  -plastic cap stops cooling by evaporation, stop water vapor loss, energy transfer by conduction is cut down cus its made from plastic

Question 19

gases expand..

Answer 19

30 times more on heating than liquids and solids

Question 20

applications of expansion by heating

Answer 20

-glass thermostats
-liquid in glass thermostats