Chapter 12 (Thermal expansion)

Questions

1. Fill in the blanks.

(i) The size of solid object increaseson heating.

(ii) A decreases take place in volume of liquid on cooling.

(iii) The volume of gas increases on heating.

(iv)The melting point of ice is denoted by 273 in Kelvin scale.

(v)The boiling point of water is denoted by 212 in Fahrenheit scale.

(vi)Density of water is maximum at 4degree centigrade.

2. Put ( √ ) mark against correct statement and ( X ) for incorrect statement.

(i) Water is filled in bulb of thermometers. ( X )

(ii) The size of 1 degree centigrade is smaller than size of 1 degree Fahrenheit. ( √ )

(iii) The size of I degree Kelvin and 1 degree Fahrenheit are equal. ( X )

(iv) The melting point of ice is denoted by 0 degree Fahrenheit scale. ( X )

3. Encircle the correct answer in following.

(i)Thermal expansion does not take place in the

(a) An automatic fire alarm (b) thermostat

(c) Fixing of iron rings on wheels (d) swing of a pendulum

(ii) The activity of metallic ball and ring shows

(a) Solid objects expand on heating (b) Solid contract on heating

(c)Solids change their nature on heating (d) there is no effect of heat on solids.

(iii) The properties of expansion and contraction of liquid due to change of temperature is used in the instrument.

(a)Barometer (b) thermometer

(c) Manometer (d) bicycle pump.

(iv) The value of 113°F on Celsius scale would be

(a) 63°C (b) 45°C

(c) 77°C (d) 81°C

(v) The value of 60°C on Fahrenheit scale would be

(a) 65°F. (b)51°F.

(c) 76°F (d) 140°F

(vi) The distance between the marks of 0° and 100° on scale of Celsius thermometer is 12 cm. If the level of mercury thread is at 4.8cm what would be the temperature in Celsius scale

(a) 72°C (b) .40°C

(c) 104°C (d) 25°C

Q4. Give short answers.

Q1. Why one end of iron girders is placed on roller in contraction of bridges and in room structure of buildings?

Answer. One end of these girders is placed on rollers so that it can move forward or backward, when thermal expansion take place in winter and summer.

Q2.Why two section of a railway track are joined together by fish plates?

Answer. Using fish plates fastened by nuts and bolts which are able to slide along the oval holes of plates. When the rails expand or contract, they slide along the fish plates, thus preventing the buckling of tracks.

Q3.When vessel full of a liquid is heated, the level initially falls and then it rises. Why it happen so?

Answer. The vessel full of liquid is made of glass, so when we start heating first vessel expand due to this expansion , water level first fall than after that liquid expand on heating so level of water rise in tube.

Q4.Why water is not used in place of mercury in thermometer?

Ans. Mercury is solidify at -38.83°C (-37.89°F) where as water solidify at 0°C (32°F), so on solidify it break the glass tube, there fore mercury is used in thermometers.

Q5. What meant by thermal expansion? Explain expansion of solid with the help of an experiment.

Answer. Thermal Expansion. Changes take place in the size of objects due to heat, usually it expand on heating and contract on cooling.

Experiment. Take a metallic rod one meter in length. Clamp its one end.

Let its other rest on straw, a needle passes through the end of straw. Theneedles act as pointer. When rods heated by burner the pointer moves, its show that length of rod has increased due to which straw rolls forward or backward.

Result: The length of a metallic rod increases by heating and it decreases on cooling.

Q6. Explain expansion of liquids with help of am experiment. Moreover, write one use of thermal expansion.

Answer. Experiment.

Fill a glass flask with coloredwater. Close its opening with cork having narrow glass tube passing through it. When the opening of flask is close with such a cork some water rise in tube. Note level of water in tube. As flask heated, water level in tube first fall than start rising. From this experiment we conclude that

Result: The volume of liquids increase on heating.

Uses. 1. Thermometer is one example of liquid expansion.2. Hydraulic breaks in cars

Q7. Why ice floats on surface of water?

Answer. Water reaches its maximum density at 4 °C. As it cools further and freeze to into ice, actually it becomes less dense and volume increase. This is why the ice floats on surface of water.

Q6. Unseen questions related to this chapter.

  1. What is -50 degrees Celsius in Fahrenheit?
  2. What is boiling point of water in Fahrenheit?
  3. Highest temperature recorded on earth.
  4. Which mathematic equation u used to convert Fahrenheit to Celsius?
  5. What human normal body temperature in Celsius andFahrenheit scale.