Chapter 10: Transfer of Heat Energy and its Effects

How does heat flow?

How does heat flow?

From a region of higher temperature to a region of lower temperature

Heat is also known as

Thermal energy

Define temperature

Degree of hotness/coldness of an object

What is the S.I. unit of temperature?

Kelvin (K)

what is the common unit of temperature?

Degree Celcius (°C)

Celcius to Kelvin conversion

0 °C ≈ 273 K

Define matter

Anything that has mass and takes up space.

What happens when something is heated?

It absorbs heat and expand, there will be in an increase in volume.

What happens when something is cooled?

It lose heat and contract, there will be a decrease in volume.

Define density

Mass per unit volume

Density formula

Density= mass / volume

Density higher when substance is heated or cooled?

Cooled. As when something is cooled, there will be a decrease in volume, while when something is heated, there will be an increase in volume.

Define conduction

Process of heat transfer through a medium or material without any movement of the medium or material.

Poor conductors of heat is called:

Insulators

Define convection:

Transfer of heat from one place to another by the movement of fluids.

How are convection currents set up?

Warm fluids, being less dense, rises.While cool fluid, being denser, sinks.

Process of conduction and convection(heating water in a metal pan)

Thermal energy is transferred from hot plate to water through metal pan by conduction.Atoms in the metal pan vibrates more vigorously when heated, and transfer energy from atom to atom by colliding with each other.Free electron diffusion also speeds up the process of conduction in metals.

Thermal energy is pass through water by convection due to density differences in water.Water near bottom of pan is heated faster.It expands, becomes less dense and rises.Cooler, denser water sinks to bottom and gets heated.Cycle repeats itself until all water is heated.

Define radiation

Transfer of heat, in form of electromagnetic waves from one place to another.It does not require a medium for transmission.

Which process is energy transferred from the Sun to solar panels?Why?

Radiation.Vacuum in space between Sun and Earth prevents conduction and convection from taking place.

Explain applications of transfer of heat energy through conduction and convection

Cooking utensils are made of metal as they are good conductors of heat.

Heating coil is placed near the base of electric kettle as warm water being less dense rises while cool water being denser sinks.which sets up convection currents.

Factors affecting radiation

Colour:

Dark:good emitters of radiant heat but poor reflectors of heat radiation

Light:poor absorbers and emitters of radiant heat but good reflectors of heat radiation

Surface:

Rough:good emitters of radiant heat but poor reflectors of heat radiation

Smooth:poor absorbers and emitters of radiant heat but good reflectors of heat radiation

Larger surface area =higher rate of absorption or emission of radiant heat

Greater difference between surface temperature of object and surrounding=the higher the rate of absorption or emission of radiant heat.

Applications of radiation

Houses are painted white as white surfaces are poor absorbers of radiant heat, so the inside of the house remains cool.

Factory roofs are painted with aluminium paint as shiny surfaces are poor absorbers of heat radiation during day and poor emitters at night.

Solar panels are painted dull black as they are good absorbers of radiant.

Effects of expansion(pouring boiling water in glass)

Glass is likely to crack due to water is poured into thick glass, as the inner surface would expand faster than outer surface.

Effects of expansion(concrete on hot days):

To prevent cracking in concrete due to excessive expansion on very hot days, expansion gaps are laid between concrete slabs and tiles.

Effects of contraction(telephone lines and electricity cables in cold weather)

To prevent snapping in cold weather due to contraction, telephone lines and electricity cables must be strung loosely

Application of expansion(open jar)

To open a jar, immerse jar’s lid in warm water.Metal lid will expand more than glass jar, this causes the lid to loosen, allowing it to unscrew easily.

Applications of expansion(bimetallic strips)

Bimetallic strips made of 2 different metals expand at different rates when heated causing them to bend. So they are used in thermostats and thermometers.

Applications of contraction(rivets)

When red-hot, rivet is put into positions to be hammered into a head and allowed to cool. As it cools, it contracts and pulls the steel plates together.