Post on 16-Dec-2015
Miyav
Heat from burning
coal produces steam,
which runs Train
locomotive
coal, petrol, wood gives heat during burning (chemical
reaction)
Miyav
How much hot?
Measured by
“temperature”
Celsius- unit
100O C0O C
How much cold?
37O C
Thermometer
Miyav
At -100 c Carbon dioxide gas becomes
solid (it is called dry ice)
At what temperature water becomes solid?
Miyav
How much hot?
1000O C-100O C 5000O CGold melts Sun’s outer surfaceGas freezes into solid
How much cold?
Measured by
“temperature”
Celsius or Kelvin
Miyav
Why ice cream is melting?
Solid
Liquid
Vapor (gas)
Low temperature
(ice cream)
High temperature
Room temperature
Miyav
How water becomes steam?
Solid
Liquid
Vapor (air)
Low temperature
High temperature
Phase
changeheating
Miyav
Heat transferred
room temperature
Heat flows from
coffee to room air
to reach
equilibrium
Heat flows from room air to
ice cream to reach
equilibrium.
So ice cream melts
why coffee
becomes cold after
some time?
Miyav
Heat transfer mechanisms
The heat is transferred along the body from one particle (molecule) to another without the movement of the particles themselves. This is called as conduction.
Conduction (occurs generally in solids)
Miyav
Metals are high conductivity material
Insulator
(conductivity very less)
conductor
(conductivity very high)
Miyav
convection (occurs generally in
fluids)
The heat is transferred from hotterportions to colder portions by theactual movement of particles of afluid is called convection.
Miyav
Radiation (can occur without any medium)
Thermal radiation is the energy radiated from hot surfaces as electromagnetic waves. It does not require medium for its propagation.
Miyav
White colour tankers & white gaps
Absorption of radiant heat by a body When radiant heat falls on a body a part of it is absorbed by it. There is an increase in its temperature due to this absorption.
Miyav
If the surface of a body is painted black it absorbs more heat than when it is painted white.
Black roof white roof
Miyav
10 Kg of coal
10 Kg of diesel
A train can run
1 Km
A train can run
4 Km
It means that for same amount of mass, It means that for same amount of mass, diesel produces larger heat compared diesel produces larger heat compared to coalto coal
Miyav
We say that We say that DieselDiesel has high has high calorificcalorific content compared to content compared to coalcoal
Calorific value of a fuel is the total quantity of heat produced when a unit mass (or volume) of the fuel is burnt completely.
Unit of calorific value is kJ/g
Miyav
coal
diesel
High calorific
So in scooters, buses, we need to carry So in scooters, buses, we need to carry less amount of fuel, since the diesel’s less amount of fuel, since the diesel’s calorific value is highcalorific value is high
petrol
wood
LPG
low calorific
High ash
zero ash
(5)
(15)
(45)
(50)
(100)
(KJ/g)