Heat transfer

Question 1

Heat will always flow from…..

Answer 1

Heat energy always flows from regions of high
temperature to regions of lower temperature. Heat
will always flow when there is a temperature difference,
no matter how small that temperature difference
is.

Question 2

There are three methods by which heat may be
transmitted.
list them and descibe

Answer 2

. conduction; transfer through a body.rate depends on thermal capacity
• convection due to change of density
• radiation.no connection material.radiation energy converted to heat energy at absorption surface

Question 3

Conduction may occur in

Answer 3

solids, liquids or gases,

although it is most clearly present in solids.

Question 4

Describe heat conduction

Answer 4

heat energy is passed on from each molecule
to its nearest neighbour, with heat flowing
away from the source of heat towards low temperature
regions

Question 5

best conductors of heat are

Answer 5

silver and copper

Question 6

Thermal conductivity is important at most stages
of a fire, but during the fully developed fire there
is the danger of fire spread.
give an example

Answer 6

As steel conducts heat
very well, a steel girder passing through a fire wall
may conduct sufficient heat through to the neighbouring
compartment (room) to start a fire there.

Question 7

Convection takes place in what states

Answer 7

This occurs only in liquids and gases

Question 8

give an example of convection in a fire

Answer 8

When a fire occurs in a building,
convection currents can convey hot gases produced
upwards through stairwells (Figure 5.5) and
open lift and service shafts, thereby spreading the
fire to the upper parts of buildings.

Question 9

describe radiation heat transfer

Answer 9

does not involve any
contact between the bodies which are providing
and accepting the heat. To all intents and purposes,
it behaves in the same way as light (“visible radiation”)
in that it travels in straight lines, will cast
shadows, and will be transmitted through some
materials and not others.

Question 10

Absolute zero is

Answer 10

1. the coldest possible temperature.
2. the point where no more heat can be removed from a system
3. This corresponds to 0 K or -273.15°C

Question 11

The specific heat capacity of a material is

Answer 11

the heat required to raise the temperature of one kilogram of the material by 1°C,

Question 12

The specific heat capacity of a material is measured in

Answer 12

Joules per kilogram per degree centigrade

J/kgºC

Question 13

In equations what letter is used as a

symbol for specific heat capacity

Answer 13

c

Question 14

What is the specific heat capacity of water

Answer 14

Water has an unusually high specific heat capacity:
4 200 J/kg per °C. There are very few substances
which have a higher value than this

Question 15

define specific latent heat

Answer 15

The heat energy that is taken in or given out by a substance when it changes state is called latent heat
latent meaning hidden

Question 16

define specific latent heat of vapourisation

Answer 16

the ammount of heat energy needed to change a unit mass of a substance from liquid to vapour without a temp change

Question 17

The definition of the specific latent heat of fusion

Answer 17

the quantity of heat required to
convert unit mass of the substance from the solid
to the liquid state without change in temperature.

Question 18

Change of state and latent heat

Change of state can be …

Answer 18

1. fusion: the substance changes from a solid to a liquid
2. freezing: the substance changes from a liquid to a solid
3. vaporisation: the substance changes from a liquid into a vapour
4. condensation: the substance changes from a vapour to a liquid

Question 19

Define thermal capacity

Answer 19

is the measurable physical quantity that shows the amount of heat required to change the temperature of a substance by a given amount

Question 20

Formula for Calculating specific heat capacity

Answer 20

Here is the equation relating energy to specific heat capacity:

E = m × c × θ

E is the energy transferred in joules, J
m is the mass of the substances in kg
c is the specific heat capacity in J / kg °C
θ (‘theta’) is the temperature change in degrees Celsius, °C

Question 21

how much energy must be transferred to raise the temperature of 2 kg of water from 20°C to 30°C

Answer 21

E = m × c × θ (θ = 30 – 20 = 10°C)

E = 2 × 4181 × 10 = 83,620 J or 83.62 kJ

Question 22

How much energy is needed to increase the temperature of 500 g of lead from 20ºC to 45ºC? The specific heat capacity of lead is 128 J/kg ºC

Answer 22

mass of lead = 500 ÷ 1000 = 0.5 kg

temperature change = 45 – 20 = 25ºC

energy needed = 0.5 × 128 × 25 = 1600 J (1.6 kJ)

Question 23

Formula for Specific latent heat

Answer 23

Here is the equation relating energy to specific latent heat:

energy (J) = mass (kg) × specific latent heat (J/kg

Question 24

How much energy is needed to melt 10 g of ice? The specific latent heat of melting for water is 334,000 J/kg

Answer 24

mass of ice = 10 ÷ 1000 = 0.01 kg

energy needed = 0.01 × 334000 = 3340 J (3.34 kJ

Question 25

Temperature and heat are not the same thing

Answer 25

temperature is a measure of how hot something is

heat is a measure of the thermal energy contained in an object.

Question 26

difference between heat and temperature

Answer 26

Heat is an energy sstored in the body measured in Joules

Temp is ameasure of degrees. how hot a body is.

Question 27

What is latent heat

Answer 27

The heat given out or taken in when a substance changes state.

Question 28

difference between heat and temperature

Answer 28

Heat is an energy sstored in the body measured in Joules

Temp is ameasure of degrees. how hot a body is.

Question 29

What is latent heat

Answer 29

The heat given out or taken in when a substance changes state.