Selina solutions concise physics class 7 icse Solutions for Chapter 5 heat

Q1) The temperature of a body rises by 1°C. What is the corresponding rise on the

(a) fahrenheit scale

(b) kelvin scale

Q2) The temperature rises by 1°F. What is the rise on the celsius scale ?

Q3) Convert 5°F to the celsius scale

Q4) Convert 40°C to the (a) fahrenheit scale (b) kelvin scale

Q5) Convert -40°F to the Celsius scale.

Q19) Iron rims are heated before they are fixed on the wooden wheels. Explain the reason.

Q1) Write true or false for each statement

(a) on touching a lump of ice, we feel cold because some heat passes from our body to the ice.

(b) heat flows from a body at high temperature to a body at a low temperature when they are kept in contact.

(c) all solids expand by the same amount when heated to the same rise in temperature.

(d) telephone wires are kept tight between the two poles in summer.

(e) equal volumes of different liquids expand by different amounts when they are heated to the same rise in temperature.

(f) solids expand the least and gases expand the most on being heated.

(g) a mercury thermometer makes use of the property of expansion of liquids on heating.

(h) kerosene contracts on heating.

(i) water is a bad conductor of heat.

(j) medium is necessary for the transfer of heat by radiation.

(k) land and sea breezes are convection currents of cold and warm air.

(l) liquids are heated by conduction and radiation.

(m) black surfaces are the poor absorbers of heat radiations.

Q2) Fill in the blanks

(a) heat is a form of _____

(b) ______ determines the degree of hotness or coldness of a body.

(c) on heating a body, its temperature _____.

(d) we use a _______for measuring the temperature of a body.

(e) the S.I unit of temperature is _____.

(f) in a thermometer, the commonly used liquid is ______.

(g) the temperature of a normal human body is____

(h) a person is said to have fever if his body temperature is more than _____

(i) a hot metallic piece is placed in tap water contained in a bucket. Heat will flow from

___ to ______.

(j) the temperature of boiling water is _____

(k) liquids expand _____than the solids.

(l) gases expand ______than the liquids.

(m) heat transfer in solids is by _______

(n) heat transfer in liquids and gases is by ______.

(o) metals are _______of heat.

(p) still air is an insulator of heat.

(q) black and dull surfaces are___ of heat.

Q3) Match the following :

Q4) Select the correct alternative

(a) if we add a lump of ice to a tumbler containing water

1. Heat flows from water to ice

2. heat flows from ice to water

3. heat flows from water to ice water is more

4. heat flows from ice to water if ice is more

(b) the temperature of pure melting ice is

1. 0°C

2. 100°C

3. 95°C

4. 98.6°F

(c) a thermometer uses

1. water

2. Mercury

3. air

4. none of the above

(d) which of the statement is correct

1. Iron rims are cooled before they are placed on cart wheels

2. A glass stopper gets tight on warming the neck of the bottle

3. Telephone wires sag in winter, but become tight in summer

4. A little is left between two rails on a railway track

(e) heat in a liquid is transferred by

1. conduction

2. Convection

3. radiation

4. conduction and radiation

(f) in the process of convection, heat travels

1. sideways

2. downwards

3. Upwards

4. ina ll directions

(g) the vacuum kept in between the walls of a thermos flask reduces the heat transfer by

1. conduction only

2. convection only

3. radiation only

4. Conduction and convection

Q1) What is heat? State its S.I. unit.

Q2) What is meant by the term temperature.

Q3) State the three units of temperature.

Q4) Name the instrument used to measure the temperature of a body.

Q5) Name two scales of temperature. How are they interrelated?

Q6) How is the size of a degree on a celsius scale ?

Q7) How is the size of a degree defined on a Fahrenheit scale?

Q9) Write down the temperature of (i) lower fixed point, and (ii) upper fixed point, on the fahrenheit scale.

Q8) State the temperature of

(i) ice point and

(ii) steam point,

on the celsius scale

Q10) What is the Celsius scale of temperature ?

Q11) What is the Fahrenheit scale of temperature ?

Q12) What is the kelvin scale of temperature?

Q13) The fig. Shows a glass tumbler containing hot milk which is placed in a tub of cold water. State the direction in which heat will flow.

Q14) Draw a neat diagram of a laboratory thermometer.

Q15) Write down the body temperature of a healthy person.

Q16) What do you understand by thermal expansion of a substance?

Q17) Name two substances which expand on heating.

Q18) Why do telephone wires sag in summer ?

Q20) Why are gaps left between successive rails on a railway track ?

Q21) A glass stopper stuck in the neck of a bottle can be removed by pouring hot water on the neck of the bottle. Explain why?

Q22) Why is a cement floor laid in small pieces with a gap in between ?

Q23) One end of a steel girder in a bridge is not fixed, but is kept on rollers. Give the reason

Q24) Describe one experiment to show that liquids expand on heating.

Q25) State one application of thermal expansion of liquids.

Q26) Describe an experiment to show that air expands on heating.

Q27) An empty glass bottle is fitted with a narrow tube at its mouth. The open end of the tube is kept in a beaker containing water. When the bottle is heated, bubbles of air are seen escaping into the water. Explain the reason.

Q28) State which expands more, when heated to the same temperature: solid, liquid or gas?

Q29) Name the three modes of transfer of heat.

Q30) Name the mode of transfer of heat in the following:

(a) solid

(b) liquid,

(c) gas

(d) vacuum

Q31) What are the good and bad conductors of heat? Give two examples of each.

Q32) Name a liquid which is a good conductor of heat.

Q33) Name a solid which is a good conductor of heat.

Q34) Select good and bad conductors of heat from the following: Copper, mercury,wood,iron,air,saw-dust,cardboard,silver,plastic,wool.

Q35) Why is an oven made of double walls with the space in between filled with cork?

Q36) Why do we use cooking utensils made up of copper?

Q37) Why is a tea kettle provided with an ebonite handle ?

Q38) In summer, ice is kept wrapped in a gunny bag. Explain the reason.

Q39) Explain why

(a) we wear woolen clothes in winter.

(b) the water pipes are covered with cotton during very cold water.

Q40) Why are quilts filled with fluffy cotton ?

Q41) State the direction of heat transfer by way of convection.

Q42) Why is a ventilator in a room ?

Q43) Why are chimneys provided over furnace in factories?

Q44) What are the land and sea breezes? Explain their formation.

Q45) Why is the freezing chest in a refrigerator fitted near its top ?

Q46) Explain briefly the process of heat transfer by radiation.

Q47) Give one example of heat transfer by radiation.

Q48) Why do we prefer to wear white or light coloured clothes in summer and black or dark coloured clothes in winter?

Q49) The bottom of the cooking utensils are painted black. Give the reason.

Q50) Draw a labelled diagram of a thermo flask. Explain how the transfer of heat by conduction, convection and radiation is reduced to a minimum in it.