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Effects of Heat and its Transmission - Coggle Diagram
Effects of Heat and its Transmission
Effects of Heat
Contraction
Loses heat
↓ vol.
Expansion
Gains heat
↑ vol.
Mass will
ALWAYS REMAIN CONSTANT
Forces (E.g.)
Bimetallic Strips
Made of 2 different metal strips, mainly
Copper + Iron
Brass => Copper
Steel => Iron
Copper expands + contracts ↑ than iron
Forces exerted due to unequal expansion/contraction of 2 metals => bends
hot => frown
cold => happy
vice versa? think Joker; opp. of everything
Breaking Iron Pin Machine
Thick bar is heated => gains heat + ↑ length
Secure bar into position via using nut to tighten it
When bar is cooled, iron pin breaks
∴ when bar contracts, large force exerted on pin, causing it to break
3 States of Matter
Liquids
Water warms up + expands when heated, ↑ water level via rising up capillary of a thin, glass test tube.
Observation: Slight drop in initial water lvl at start of experiment
due to heat source causing glass test tube to expand + ↑ in vol.
Water cools down + contracts, ↓ water level via going down the capillary of a thin, glass tube.
Gases
Highest average KE of particles in sub among 3 states
Great changes in vol.
When Air Heated => Expands, drop of water in capillary of test tube ↑
When Air Cooled => Contracts, drop of water in capillary of test tube ↓
Solids
Lowest average KE of particles in substance among 3 states
Smallest changes to vol.
Metal gains heat + expands when heated, and cools down + contracts when cooled.
Temperature
Usage of Thermometers
SI unit => Kelvin (K)
x °C +
273.15
= ( 273.15 + x ) K
0 K =
absolute zero
Particles move ↑ vigorously and further apart as they gain heat, hence only ↑ vol. and mass is constant; vice versa
Introduction
when substances heated/cooled => expand/contract
heat flows from hot region to cold region; think about how Diffusion works
different substances expand/contract and change in vol. differently
IRL
Rectifying Problems
Overhead Wires
Not stretched too tightly => prevent wires from breaking
Bridges
Usage of rollers / expansion gaps =>
allow movement
1 end is free while other is fixed => allow bridges to move as bridges become longer on hot days + shorter on cool days
Concrete Roads + Paths
Small gaps every few m =>
allows expansion
in hot weather
Pipes Carrying 热水 / steam
Have 'expansion' loops. => expanding pipes may cause pipes to buckle + break
MRT Tracks
small gaps in tracks =>
allow expansion
to prevent bending/buckling
Glassware
Inner Layer ( contact with water ) expand ↑ quickly than Outer Layer(cooler).
Unequal expansion
=> breaks glass
Useful Applications
Bimetallic Thermometer
Usage of coiling Bimetallic Strips
As Temperature Varies, two metal strip expand / contract unequally => coil to tighten / unwind.
Example: Car Thermometers
Pointer moves over scale to show temp.
Thermostat
Usage of Bimetallic Strips
Keeps temp. constant
electric iron
refrigerator
rice cookers
Conduction
= heat transfer thru material without obvious movement of medium
E.g. Metal atoms gain heat from flame, collide with neighbouring atoms, transfer energy + vibration ↑
Best Conductor: Metals
Conductors =>
transfer heat quickly
from one place to another.
Insulators: Liquids, gases + non-conductive materials (wood)
Best Insulator: Vacuum => no particles
Insulators =>
reduce heat transfer
from one place to another
Convection
= transfer of heat of which hot air rises and cold air sinks
IRL
热水 System
Hot water from boiler ( density ↓ ) rises while water from cold water tank (denser) sinks into boiler
Sea Breeze
Hot days => Land heats up faster than sea, ∴ hot air from land rises while cold, denser air over sea replaces hot air
Electric Kettle
Heating element found below it
热水 ( density ↓ ) rises + denser cold water sinks
Cooling Rooms
ACs are placed high up to cool hot air => cool air from AC sinks + allows hot air to rise due to space displacement
Warming Rooms
Heater placed below => sinking cold air can heat up + rising hot air allows space for cold air to sink
Land Breeze
Nighttime => Land cools faster than sea, ∴ hot air rises over sea, cold air over land replaces hot air
水
When Water Heated => Expands, as molecules move faster, spread further apart; density ↓.
Density => Hot < Cold
∴, hot, ↓ dense water rises while cooler, ↑ dense water sinks to take up the space displaced by former
∴ movement =>
convection current
Air
When Air Heated => becomes less dense + rises
When Air Cooled => becomes denser, sinks + forms
convection current
Radiation
= Heat transfer without medium ( 3 states of matter )
Objects warmer than surroundings give out heat as radiation
Absorption = take in energy
Absorbers ∝ radiators.
Good absorbers & radiators: Black, dull + rough
Poor absorbers & radiators: White, shiny and smooth
Dependent Variables
Surface Area
↑ surface area, ↑ heat gained or lost/sec
Object's Temperature
↑ temp diff between object + surrounding => ↑ heat gained or lost/sec
Surface's Nature
Blacker / Rougher => ↑ heat gained/sec, and vice versa
IRL
Electric Kettle
Shiny surface => poor radiator of heat. ∴, allows water inside kettle to stay hot for ↑ time as heat is retained
Petrol Tanks
have white/shiny surfaces =>
reflect radiation
( sun ) ∴, prevents petrol from heating up + igniting
White shirt absorb ↓ radiation ( sun ) + keep people cool
Radiation = radiate/give out heat
Global Warming
Heat transfer from sun to Earth's surface via Radiation in vacuum ( space )
Heat is then transferred thru solid ground via Conduction
Causes air around land + sea to be warm
Since objects radiate heat, ground radiate heat back to atmosphere
Heat in atmosphere spread around earth =>
convection current
Caused by
greenhouse gases ( CO2 ) => trap heat + keep earth warm. High CO2 => global warming
Natural
Volcanic Eruption
Organisms: Respiration / Natural Decomposition
Man-made
Burning of Fossil Fuels ( petrol, diesel, coal ) in power stations, motor vehicles
Carbon Footprint
= amount of CO2 produced / year
Measurements: kg/year or tonnes/year
Effects
Extreme Climate Conditions
Melting of ice caps => ↑ sea lvl
Some radiation is absorbed by greenhouse gases in atmosphere, while some escape to space
