thermal physics

Question 1

what is evaporation

Answer 1

when the more energetic particles near the surface of the liquid escape as they turn in to vapour. This decreases the average kinetic energy of the particles in the liquid which is directly proportional to the temperature of the liquid and thus the liquid cools down

Question 2

what are the differences between evaporation and boiling

Answer 2

• evaporation occurs at all temperatures while boiling only occurs at a certain temperature
• evaporation is a surface phenomena while boiling i s a bulk phenomena

Question 3

factors affecting rate of evaporation

Answer 3

• temperature
• surface area (larger better)
• draught (air movements better)
• humidity (lower better)

Question 4

thermal expansion in states of matter

Answer 4

solid- little expansion, requires large amounts of energy
liquid - some expanison, some energy required
gases - lots of expansion, lots of energy required

Question 5

application of thermal expansion

Answer 5

-liquid in bulb thermometer
-bimetallic strips
( extra room should be provided for solids to expand in railway tracks)

Question 6

what is temperature

Answer 6

physical property that measures how hot or cold an object is

Question 7

how to make a thermometer

Answer 7

• use fixed points of temperature (etc melting temperature of ice and boiling tmeperature of pure water) to work out the temperatures inbetween

Question 8

properties of thermometers

Answer 8

• sensitivity
• range
• quick response time
• linearity

Question 9

what is sensitivity of thermometers

Answer 9

-ability to detect a change in temperature, if the physical property changes greatly for a small change in temperature that indicates that your thermometer is sensitive

Question 10

what is range of thermometer

Answer 10

difference between highest and lowest temperature a thermometer can measure

Question 11

quick response time of thermometer

Answer 11

time taken for a physical property to detect and response to a change in temeprature

Question 12

linearity

Answer 12

the chosen property varies linearly with temp throughtout its range, it changes at a steady rate

Question 13

how to increase sensitivity of liquid in glass thermometers

Answer 13

• increase volume of liquid in the bulb

- decrease cross-sectional area of stem

Question 14

how to increase range of liquid thermometer

Answer 14

use a longer tube

Question 15

what is thermal capacity

Answer 15

the amount of heat energy required to raise the temperature of that object by 1c or the amount of energy given out by the object when it cools by 1c

Question 16

formula for thermal capacity

Answer 16

energy required = thermal capacity x amount of temperature raised

Question 17

what is specific heat capacity

Answer 17

the amount of thermal energy required to raise the temperature of 1kg of that substance by 1c

Question 18

formula for specific heat capacity

Answer 18

thermal capacity = specific heat capacity x mass

Question 19

formula for change in energy

Answer 19

change in energy = mass x specific heat capacity x change in temperature

Question 20

what is latent heat

Answer 20

energy required to change the state of a substance (the energy required to break the bonds holding molecules together)

Question 21

latent heat of fusion

Answer 21

energy required to turn a solid into a liquid

Question 22

latent heat of vaporisation

Answer 22

energy required to turn a liquid into a gas

Question 23

what is conduction

Answer 23

the main method of thermal energy transfer in solids

Question 24

what is convection

Answer 24

the main way heat travels through liquids and gases

Question 25

process of convection currents

Answer 25

• the molecules push each other apart, making the liquid/gas expand
• this makes the hot liquid/gas less dense than the surroundings
• the hot liquid/gas rises and the cooler surrounding liquid/gas moves in to take its place
• eventually the hot liqud/gas cools, contracts and sinks back down again

Question 26

how does heat travel through a vaccuum

Answer 26

thermal radiation, the way heat reaches us from the sun

Question 27

factors affecting infra-red emission

Answer 27

• the higher the temperature of the object the more radiation it will emit
• the larger the surface area of the object the more infrared radiation it will emit