Heat
Q I Choose the correct answer.
1 Bimetallic strip is made up of
Metals with different linear expansion coefficient.
2 Specific heat depends on mass of material.
3 In a thermostat device which parameter remains approximately constant temperature.
4 Unit of co-efficient of linear expansion K-1
5 Density of water is maximum at 4 0C
Q II Fill in the blanks.
1 Unit of heat capacity is Joule /Kelvin of Joule /Celsious
2 On heating a rod , its length increases.
3 Unit of latent heat is J /Kg
4 Expression for latent heat of fusion = L= Q/m
5 The atomic mass of an atom is 23 and its atomic number is 11 , the atom has ---------------Q III Answer the following
1
2
Mention the effects of heat on a substance
The effects of heat are
I)
Thermal expansion
II)
Increase in temperature
III)
Change of physical state
Give two illustrations of thermal expansion from day today life
i)
When railway lines are laid, a space is left between successive rails in order to allow for
expansion during summer.
ii)
Allowances are made for expansion in mounting girders for iron bridges.
3
What is bimetallic strip? Mention any two applications of it.
When two strips made of different metals are joined together form a bimetallic strip
Applications are i) Thermostat switch which regulates the temperature of the electric iron
ii) They are used in refrigerators.
4
Define heat capacity of a substance . Mention its unit
The specific heat of a substance is the quantity of heat required to raise the temperature of unit
mass of it through unit temperature. Unit of specific heat is J /Kg K
5 Give two illustration of high heat capacity of water
i)
ii)
Hot water bags are used for the fomentation as water does not cool quickly as it has high
specific heat capacity.
Water is used as a coolant in the radiators of cars. It absorb more heat without much rise
in temperature as it has high heat capacity.
For figure refer page no. 40 fig 3.2 a
and
3.2 b
A metal ball and a metal ring of suitable radius is taken. Such that the ball can just pass through the
ring when both are the same temperature . then heat the metal ball and try to pass it through the ring
It will not pass through the ring .Keep the metal ball on the ring for some time, it fall through the ring.
Since on cooling it contract, On heating the metal ball increase in its volume.
7
Define latent heat of vapourisation
The latent heat of vapourization of any liquid is the amount of heat required to convert unit mass
Of the liquid at its boiling point completely into vapour, with rise in temperature.
8 Ice at 00C is a better coolant than water at 00C, justify
Ice at 00C is a better coolant than water at 00C, as ice at 00Cabsorb heat from its surrounding
to melt but water at 00C is already in liquid state.
IV solve the following problems
1.The length of a brass scale is 1m at 280C. If the coefficient of linear expansion of brass is 18X10-6/0C
what is its new length at 680C ?
A L2 – L1 =𝛼L1( T2 – T1 )
L1 = 1m T1 = 280C, T2 = 680C
L2 – 1 = 18 x 10-6 x 1 (68 -28)
L2 – 1 = 18 x 10-6(40)
L2 – 1 = 720 x10-6
L2 = 0.00072 + 1
α= 18x10-6/0C
L2 = 1.00072m
2.A body of mass 0.5kg requires 3000 J of heat in order to raise its temperature from 350C to 450C.
Calculate its specific heat.
A
S = Q / mΔT
Q = 3000 J,
m = 0.5 kg
T1 = 350C
T2 = 450C
S = 3000/ 0.5 ( 45 – 35 ) = 3000/0.5X10 = 3000/5 = 600J/kg/0C
3.A metal rod of length 0.5 m at 200C becomes 0.5006m at 950C. Find the coefficient of linear expansion.
A
α = L2 – L1/ L1 ( t2 – t1 ) = 0.5006 – 0.5/ 0.5 ( 95 – 20 )
α = 0.0006/ 0.5 X75 = 0.006/375
= 16X10-6/oC
IV Match the following
A
B
1 Heat
a form of energy
2 bimetallic strip
made of two metals with different linear expansivity
3 Density of water
maximum at 40C
4 Specific heat
J/kg0C