Heat
Choose the right answer .
1.Bimetallic strip is made up of --------
a) metals with different linear expansion coefficient
b) metals with same linear expansion coefficient
c) metals with same surficial expansion coefficient
d) metals with different length
2. Specific heat depends on ------------
a) nature of the material b) mass of the material
c) shape of the material d) colour of the material
3. Unit of coefficient of linear expansion ----------
a) K-1 b) N-1 c) J-1 d) S-1
4. In a thermostat device which parameter remains approximately constant-------
a) volume b) pressure c) temperature d) mass
5. Density of water is maximum at --------
a) 00C b) 40C c) 4K d) 1000C
Fill in the blanks with right answer
1. Unit of heat capacity is -------------( J/ K OR J/ 0C )
2. On heating rod , its length ---------- ( increases )
3. Unit of latent heat is -------------- (joule /kg )
4. Expression for latent heat of fusion is -------------- (joule /kg )
Match the followings :
1. Heat - J/Kg0C (4)
2. Bimetallic strip - maximum at 40C ( 3)
3. Density of water - Pair of junction made up of two dissimilar metals
4. Specific heat - made up of two metals with different linear expansion (2)
melting
-a form of energy ( 1)
Answer the following questions
1.Mention the effects of heat on substances.
Substances a) changes in their physical states b) changes chemically and
c) expands on heating
2. What is thermal expansion ?
Substances expands on heating . This is called thermal expansion
3. Write types of thermal expansion of solids .
Types of thermal expansion are a) linear expansion b) surfacial expansion and
c) cubical/ volume expansion
4. Define linear expansion ?
Increase in length of a substance due to heat is called linear expansion.
5. Define surfacial expansion ?
Increase in area of a substance due to heat is called surfacial expansion.
6. Define cubical/ volume of expansion ?
Increase in volume of a substance due to heat is called cubical/ volume of expansion.
7. Write the unit of coefficient of linear expansion, coefficient of surfacial expansion and coefficient of cubical/ volume expansion .
K-1 or 0C
8. Give illustrations of thermal expansion of solids in day-to-day life .
a) In railway lines about a quarter of an inch space is left between any two successive rails.
b) allowances are made for expansion in mouldings girders for iron bridges.
c) in riveting boiler plates red hot rivets are used.
d) electrical wires are hung up slack in summer & contract in winter.
e) concrete roads are laid in sections with soft pitch between the sections.
f) thermal expansion is used to fit metal axles onto wooden wheels of country carts.
9. What is bimetallic strip ? write its applications .
Metal strip made up of two metals with different linear expansion is called bimetallic strip.
bimetallic strip are used in
a)thermostat switches.
b) thermostat switches are used in electric iron box, air conditioner, ice plants, refrigerators, thermometers etc
10. What is anamolous expansion of water ? Write its biological importance .
Water contracts on heating from 00C to 40C but expands on heating above 40C . This behavior of water is called anamolous expansion of water. Due to this property of water even the atmospheric temperature comes below 00C, water in the ocean & lakes remains in liquid state. Hense aquatic life keeps safe.
11. Define heat capacity ? What is the unit of heat capacity ?
The amount of heat required to rise the temperature of a substance by 10C or 1 kelvin is called heat capacity.
unit of heat capacity is Joule /kelvin or joule / 0celsius
12. What is specific heat capacity ? Write unit of specific heat capacity
The amount of heat required to rise the temperature of unit mass of a substance by unit temperature is called specific heat capacity.
unit of specific heat capacity is J / kg.k
13. Write the formula for spe cific heat capacity.
specific heat capacity = heat capacity of the body
mass of the body increased temperature
Q = mst Here Q= heat capacity, m= mass of the body,
t= increased temperature, s= specific heat capacity
14. Give consequences of high specific heat capacity of water.
a) water is used as coolant in radiators of cars.
b) hot water bags are used for fomentation
c) Coastal area are cooler in summer & hotter in winter compared to other areas as water heated & cools slowly.
15. Describe an experiment to demonstrate the cubical expansion in solids .
The apparatus are as shown in figure. The metal ball can pass through the ring but it cannot pass through the ring after heating the ball. Again metal ball can pass through the ring after cooling . Hense this experiment demonstrate the cubical expansion in solids by heat.
16. Define latent heat ?
The quantity of heat required to change the state of matter without changing the temperature is called latent heat.
17.Write the unit of latent heat.
Unit of latent heat is J/Kg
18. Define latent heat of fusion ?
The quantity of heat required to change the solid state of matter to liquid state without changing the temperature is latent heat of fusion
19. Define latent heat of vaporisation ?
The quantity of heat required to change the liquid state of matter to gaseous state without changing the temperature is latent heat of vaporisation
20. Ice at 00C is a better coolant than water at 00C . Justify.
Because Ice at 00C has more latent heat than water at 00C
21. Write the formula for latent heat .
Q = mL
Here Q = heat m= mass, L=latent heat
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