RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Rajasthan Board RBSE Class 7 Science Chapter 15 Temperature and Heat

RBSE Solutions for Class 7 Science

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

RBSE Class 7 Science Temperature and Heat Intext Questions and Answers

Page No 146. 

Question 1.
List the names of some objects in table whether they are hot or cold: Ice, Tea (ready), Flame, Cold drink, Body in fever.
Answer:
Table : Name of some hot and cold objects
RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat-1

Question 2.
Generally how do you decide that the object is hot or cold?
Answer:
We often decide it by touching or by seeing the objects.

Question 3.
Is our sense of touch reliable to know about the hot or cold object?
Answer:
No, our sense of touch is not reliable to know about the hot or cold objects.

Page No 147.

Question 4.
What is the highest and lowest scale value of laboratory thermometer?
Answer:
The highest and lowest scale value of laboratory thermometer is generally 10°C to  110° C. It is called the range of thermometer.

Question 5.
How is temperature measured by a thermometer?
Answer:
Dip the bulb of thermometer in the object or material whose temperature is to be measured. wait till mercury surface level becomes stable. Note the reading on the thermometer. It is temperature of the object.

page No 148.

Question 6.
How do we find the body temperature from clinical thermometer?
Answer:
By putting the bulb of thermometer under the tongue inside mouth, hold it there for some time and then take it out. Now by seeing the level of mercury and note down the reading. It is the body temperature

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

page No 150.

Question 7.
Due to heat transfer the objects either become hot or cold. Why does this happens?
Answer:
The temperature of the object which releases heat becomes low whereas the temperature of the object which receives heat becomes more.

page No 151.

Question 8.
Does heat conduction happen easily in all objects?
Answer:
No, heat conduction occurs only in the objects which are good conductors of heat: Heat conduction does not occur in bad conductor objects.

page No 152.

Question 9.
Why wood, plastic, etc. are less hot?
Answer:
Wood. plastic, etc. are bad conductor of heat. They do not conduct heat easily through them. Hence they are less hot.

Question 10.
Why hollow bricks are used during the building construction?
Answer:
By using hollow bricks during the building construction.. there is less effect f heat or cold on rooms in summer or winter.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

page No 154.

Question 12.
It is possible to transfer heat without any medium (vacuum).
Answer:
Yes, heat transfer is possible through radiation without medium (vacuum). No medium is required for heat conduction through radiation.

page No 155.

Question 13.
Why do we feel more heat by wearing dark coloured cloths during summers?
Answer:
Dark coloured objects absorb more radiations, so these objects become hot. Due to this reason we feel more heat by wearing dark coloured clothes during summer.

RBSE Class 7 Science Temperature and Heat Text Book Questions and Answers

Choose the correct option:

Question 1.
Which material is used in Laboratory thermometer?
(a) Sodium
(b) Mercury
(c) Melted aluminium
(d) Shining water
Answer:
(b) Mercury

Question 2.
In a heat transfer method when molecules themselves move from one place to another to transfer heat, it is called:
(a) Conduction
(b) Convection
(c) Radiation
(d) Conduction and radiation both
Answer:
(b) Convection

Fill in the blanks with suitable words:

  1. Degree of hotness or coldness of an object is called ……………………
  2. A metal spoon is dipped into ice cream pan for few moments then it will become ……………………
  3. A layer of copper is adhered at bottom of steel pan because copper is good …………………… of heat.
  4. The heat flows form …………………… temperature object to …………………… temperature object.
  5. Air and water are …………………… of heat.

Answer:

  1. Temperature
  2. Cold
  3. Conductor
  4. More, less
  5. Bad conductor

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

In the following statements, tick T against those which are true, and F against those which are false:

  1. If we add 1 litre of 35°C water in 1 litre of 55°C water then the mixture will have a temperature of less than 30°C. (T/F)
  2. Utensils for cooking food are made up of metals because metals are good conductors of heat. (T/F)
  3. The house, which have outer wall painted with white colour, are less hot in summer day. (T/F)

Answer:

  1. F
  2. T
  3. T

Long Answer Questions:

Question 1.
Explain the differences between good conductor and bad conductor of heat with examples.
Answer:

  1. Good conductor of heat : The objects in which heat transfer occurs easily are called conductors of heat.
    Example : Aluminium, iron, copper, etc. arc good conductor of heat.
  2. Insulators of heat : The objects in which heat cannot be transferred easily are called bad conductors of heat.
    Example : wood, plastic, woolen clothes, etc. are bad conductors of heat.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 2.
What are the different methods for heat transfer? Explain the different in each.
Answer:
Transfer of heat occurs from one object to other object or from higher temperature to lower temperature region. There are mainly three methods for heat transfer:

  1. Transfer of heat by conduction
  2. Transfer of heat by convection
  3. Transfer of heat by radiation

1. Conduction:
The transfer of heat is solid objects occurs by conduction. The materials which allow heat to pass through them easily are called heat conductors. For example:
Metals like aluminium, iron, copper, etc.

2. Convection:
By this mechanism, the liquid molecules itself move from one place to another to transfer heat. This method of heat transfer is called convection of heat. Heat transfer in liquids occurs via this method.

3. Radiation:
The method in which heat transfer takes place without any medium (in vacuum) is called radiation. Radiation is electro-magnetic waves. Like the heat radiated from sun reaches the earth as light through vacuum.

Question 3.
When we put objects in sun light, why do black objects get more heated up as compared to lustrous objects although having same size and shape?
Answer:
Black objects absorb more radiations, so they become more hot quickly and their temperature increases while lustrous objects absorb radiations in lesser amount, so these are heated up less comparatively.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 4.
Give the reason for formation of hot currents in sea?
Answer:
Sun rays fall directly all around the equatorial line as compared to poles. That is why the water in oceans is more hot near the equatorial circle as compared to poles. This water being remains on the surface and as such flows towards the polar region. The hot water that flows in such a way is called hot water current.

Question 5.
Why is the handle of cooking utensils made with ebonite or wood? Give reasons.
Answer:
Both ebonite and wood are bad conductor of heat. The cooking utensile are made up of metals, so they become hot during cooking and also their handles become hot. But if these handles are made up from ebonite or wood, they are not heated up due to their bad conductor of hot nature and so we can hold them easily.

Question 6.
With the help of a diagram, explain the heat conduction procedure.
Answer:
Mechanism of heat conduction.

Experiment:
Take a broken cycle spoke or thin straight iron wire and paste a few pieces of wax at equal distance on it. Put one end of wire on a table, put a brick or stone on it under the brick or stone as shown in figure. Heat the other end of wire with candle. We see that wax on heating end of wire drops down first, then next pieces of wax are dropped sequentially. This happens because by heating one end of the wire, heat is transferred towards the cold end. This method of heat transfer is called conduction. The transfer of heat in solid objects occurs by conduction.
RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat-2

Question 7.
How are we protected in winter by wearing woolen clothes ? State the reason.
Answer:
Air is trapped in tiny pores of woollen clothes. Wool and air being bad conductors of heat, do not allow body heat to go out and we are protected from cold. So we should wear woollen clothes in winter.

RBSE Class 7 Science Temperature and Heat Important Questions and Answers

Objective Questions:

Question 1.
The degree of hotness or coolness of any objects is called ……………..
(a) Pressure
(b) Temperature
(c) Conduction
(d) Insulator
Answer:
(b) Temperature

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 2.
‘In the following which one is the instrument for measuring temperature of objects ……………..
(a) Manometer
(b) Barometer
(c) Thermometer
(d) All
Answer:
(c) Thermometer

Question 3.
What is the average temperature of human body?
(a) 98.6°F
(b) 98.3°F
(c) 98.8°F
(d) 98.1°F
Answer:
(a) 98.6°F

Question 4.
Following is the conductor of heat ……………..
(a) Wood
(b) Plastic
(c) Wool
(d) Copper
Answer:
(d) Copper

Question 5.
Body temperature in fever ……………..
(a) decreases
(b) increases
(c) both (a) and (b)
(d) None of these
Answer:
(b) increases

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 6.
The temperature of any object, place or person is measured by ……………..
(a) Stethoscope
(b) Microscope
(c) Thermometer
(d) None of these
Answer:
(c) Thermometer

Question 7.
For weather temperature measurement, which thermometer is used ……………..
(a) Maximum-minimum thermometer
(b) Laboratory thermometer
(c) Clinical thermometer
(d) Normal thermometer
Answer:
(a) Maximum-minimum thermometer

Question 8.
Which medium is required for heat transfer through radiation method ……………..
(a) Solid
(b) Liquid
(c) Gas
(d) Vacuum
Answer:
(d) Vacuum

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 9.
Heat is reached from sun to earth ……………..
(a) by radiation
(b) by conduction
(c) by convection
(d) By ah of these type
Answer:
(a) by radiation

Fill in the blanks:

  1. Sun rays falls ………………………… all around the equatorial line. (Directly/obliquely)
  2. Air flows from ………………………… pressure region to pressure region. (Higher-lower/lower-higher)
  3. Most space between earth and sun is ………………………… (Vacuum/convection)
  4. The method in which heat transfer takes place without any medium (in vacuum) is called ………………………… (Convection/Radiation)

Answer:

  1. Directly
  2. Higher lower
  3. Vacuum
  4. Radiation

Match the column I with column II

Question 1.
RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat-3
Answer:

  1. (b)
  2. (c)
  3. (a)
  4. (e)
  5. (d)

Very short Answer type Questions:

Question 1.
What is called temperature?
Answer:
The hot temperature or cold temperature of an object can be known by a characteristic which is called the temperature of an object.

Question 2.
Which instrument is used in measuring temperature of an object?
Answer:
Thermometer is used in measuring temperature of an object.

Question 3.
What is called range of thermometer?
Answer:
Thermometer has printed scale on it. It. is called the range of thermometer.

Question 4.
What is the range of laboratory thermometer?
Answer:
it is generally from – 10°C to 110°C.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 5.
What is the range of clinical thermometer in degree Celsius and degree Fahrenheit?
Answer:
The range of clinical thermometer is degree Celsius is 35°C to 42°C or 94°F to 108°F.

Question 6.
What is the average human body temperature.
Answer:
It is 37°C or 986°F.

Question 7.
What is called clinical thermometer?
Answer:
The thermometer which is used to measure body temperature, is called clinical thermometer.

Question 8.
The. level of mercury (in thermometer) does not change even when it is taken out from mouth. Why this happens?
Answer:
The mercury level neither rises nor drops in clinical thermometer after taking it out from mouth. It is due to the presence of a kink near the bulb which does not let the mercury level to drop or rise b itself. So, each time before taking the temperature it is held firmly in hand and a few jerks are given so that the level of mercury goes down.

Question 9.
Name the methods of heat transfer.
Answer:

  • Conduction method
  • Convection method
  • Radiation method.

Question 10.
Heat transfer occurs from which temperature to which temperature?
Answer:
Heat transfer occurs from higher temperature region to lower temperature region.

Question 11.
Up to when heat transfer occurs between hot and cold objects?
Answer:
The hot or cold objects exchange heat till the temperature of both becomes the same.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 12.
What is conduction in heat transfer process?
Answer:
The transfer of heat from one end to other end in solids is called conduction process.

Question 13.
Give examples of conductors of heat.
Answer:
Aluminium, iron, copper, metals etc.

Question 14.
Give examples of insulators of heat.
Answer:
Wood, stone, plastic, wool, etc.

Question 15.
What is called convection of heat?
Answer:
The heat transfer takes place through the movement of molecules themselves in liquids. This method of heat tranfer is called convection method.

Question 16.
Does convection of heat occur in air?
Answer:
Yes, air also convents heat. Air molecules also become lighter after absorption of heat (with low density) and move bottom to the top. The upper cold molecules of air move downward to gain heat

Question 17.
What is called Radiation?
Answer:
The method in which heat transfer occurs without medium (in vacuum), is called Radiation.

Question 18.
What is meant by vacuum?
Answer:
Place where no air or other particles are present, is called vacuum.

Question 19.
What is comparative state of temperature?
Answer:
Hot or cold is the comparative state of temperature. For example, temperature of ice is lower than hot water but temperature of boiled water is greater than ice or low heated water.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 20.
What is called sea breeze?
Answer:
The cooler air from the sea blows towards the land. It is called sea breeze.

Question 21.
What is called land breeze?
Answer:
The cool air from land blows towards the sea side. This is called the land breeze.

Short Answer Type Questions:

Question 1.
What are the types of thermometer? Write their names.
Answer:
The instrument used to measure temperature of any object is called thermometer. These arc of many types, eg.

  • Laboratory thermometer
  • Gas thermometer
  • Alcohol thermometer
  • Digital thermometer
  • Clinical thermometer
  • Maximum-minimum thermometer

Question 2.
What precautions should be taken during measurement of temperature?
Answer:

  • Never put the bulb of thermometer in direct flame or sunlight.
  • Carefully drop the garbage in dust bin If thermometer is broken.
  • The mercury of thermometer must not go in the mouth. It is poisonous in nature.
  • The bulb of thermometer should not be touched with bottom of pot or its walls.
  • During taking reading, thermometer should be erect, not oblique.
  • Hold thermometer carefully and also jerk it carefully if needed.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 3.
Comment on the following:

  1. Maximum-minimum thermometer
  2. Digital thermometer.

Answer:

  1. Maximum-minimum thermometer – The different thermometers arc used for different applications. They are used to provide maximum and minimum temperature in whether reports.
  2. Digital thermometer – This thermometer does not contain mercury. Mercury is a toxic material and if a thermometer breaks and its mercury lifters, it may be harmful to the body if any kind of intake occurs. So, nowadays, digital thermometer ¡s in common use.

Question 4.
What is meant by heat?
Answer:
Heat is a type of energy which transfers from one object to another object. Due to this transfer of heat, objects can become hot or cold i.e. temperature of the objects can be increased or decreased.

Question 5.
State two specifications related to transfer of heat.
Answer:

  • Heat transfer always occurs from higher temperature to lower temperature region.
  • Object which loses heat, becomes cold and the object which gains heat, becomes hot
  • The hot and cold objects exchange heat till the temperature of both becomes the same.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 6.
Explain with an experiment about the change in temperature.
Answer:
Experiment:
Temperature increment –

decrement:
Take 2 litre water in a stainless steel pot or other container and warm it till boiling. No remove the pot from the flame. Take water with normal temperature in a glass or test tube and measure its temperature. Now, put the test tube or glass into the hot water pot for some time and again measure the temperature.

We will find that the temperature of cold water rises and temperature of hot water decreases a little. Thus “The temperature of the object which releases heat becomes low whereas the temperature to the object which receives heat becomes more”.

Question 7.
Write the names of heat transfer method.
Answer:
Following are the methods of heat transfer:

  • Heat transfer by conduction : Occurs in solid objects.
  • Heat transfer by convection : Occurs in liquid objects.
  • Heat transfer by radiation : It does not require any medium for heat transfer.

Question 8.
Differentiate between different method of heat transfer.
Answer:
Following are three methods of heat transfer:

  1. Conduction
  2. Convection
  3. Radiation.

Differences between these are as follows:
RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat-4

Question 9.
When exchange of beat occurs between two objects?
Answer:
The exchange of heat occurs between two objects till the temperature of both becomes the same. That is why we can say that heat exchange between cold and. hot objects occurs till the temperature become same for both the objects.

Question 10.
Stainless steel pot usually has a copper base, why?
Answer:
Copper is a good conductor of heat, so it becomes hot quickly and gains more temperature. So this ¡s the reason, stainless steel pot usually has a copper base.

Question 11.
During summers, why is it less troublesome to walk bare foot on a mat or carpet as a covering of heated floor.
Answer:
Floor absorbs more from incident radiations, so becomes hot. By covering floor with mat or carpet, which is bad conductor of heat, it does not become hot easily. Hence. it is less troublesome to walk bare foot on a mat or carpet as a covering of heated floor.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 12.
How are we protected from cold if the body is covered by two blankets?
Answer:
During winter, when the body is covered with two blankets simultaneously, a large layer of air is formed between the two blankets and gets trapped and we are protected from cold.

Question 13.
What is the role of ventilators near the ceilings of rooms in houses?
Answer:
Generally the air we exhale is hot and of low density compared to normal air. It rises up towards the roof and exits from ventilator near the ceiling and fresh air enters from doors and windows.

Question 14.
How does air flow?
Answer:
Air flows from high air pressure to low air pressure area. When a place has high temperature then its air becomes hot, rises up and expands. Because of this air pressure at that place is reduced. Then air starts to flow from cool plane to hot place.

Question 15.
What are sea breeze and land breeze?
Answer:
During the day, the land gets heated up more than the sea water. The cooler air from the sea blows towards the land. It is called sea breeze. But at night the land gets cooler fast. The cool air from land blows towards the sea side. this is called the land breeze.

Question 16.
Why days are hotter and nights are cooler in deserts?
Answer:
Sand has a characteristics that it is a good absorbed as well as good emitter of heat energy. Hence during day time, sand becomes hotter by absorbing heat radiations from sun while in night it becomes cooler by emitting heat energy quickly. So. days are hour and nights arc cooler in desert area.

Question 17.
Why nights with cloudy sky are hotter than the nights with clear sky?
Answer:
Earth becomes hotter by absorbing radiations from sun during day time and in night, it releases heat radiations. When sky is clear in night, then these emitted radiations go in space which results in decrement in temperature of earth. But, due to cloudy sky, the emitted radiations could not go into the space, even return back towards earth. So temperature of earth is not decreased. So cloudy nights are hotter than clear nights.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 18.
Why temperature on mountains is lower even in summer?
Answer:
Because surface on mountains is irregular and mostly covered. Sun rays also do not strike directly on mountains. Due to this reason, sun rays spread over a large area. So temperature on mountains is lower even in summer.

Question 19.
What are the types of oceanic currents? Define.
Answer:
Oceanic currents arc of two types:

  1. Hot water currents
  2. Cold water currents

1. Hot water currents:
Sun rays falls directly all around the equatorial line as compared to poles. That is why the water in oceans is hotter near the equatorial circle then the poles. This water remains on the surface and flows towards the polar region. The hot water that flows in such a way is called hot water current.

2. Cold water currents:
The water around the pies is heavy due to its coolness. It flows from poles to equatorial circle. These types of currents are called cold water currents.

Question 20.
What are infra red radiations? From where are they released? What are the effects of these radiations?
Answer:
Infrared Radiations:
These are the waves by which radiation of heat occurs. Infra red radiations released from earth. Most part of this infrared rays emitted from earth goes into space and earth’s temperature cools down at night due to this reason.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Essay Type Questions:

Question 1.
What is laboratory thermometer? How it is used? Explain with diagram.
Answer:
Laboratory Thermometer:
It is a long glass tube with a thin internal glass tube of equal diameter filled with mercury. One end of the tube is joined with bulb and other end is closed. Thermometer has printed scale on which is generally a Celsius scale. In the laboratory thermometer, normally – 10° C to 110°C markings are seen. It is called the range of thermometer. To measure the temperature of a liquid, dip the bulb of thermometer in that liquid and wait till mercury surface level becomes stable. Note the readings on the thermometer.
RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat-5

Question 2.
What is clinical thermometer? How body temperature is measured by this? Explain with diagram.
Answer:
Clinical thermometer:
The thermometer which is used to know the temperature of our body is called clinical thermometer. It has two scales marked, one Celsius and another Fahrenheit. this glass tube is also filled with mercury. The clinical thermometer is designed to measure the temperature of human body only which is between 35°C to 42°C.

Thus the temperature range of clinical thermometer is between 35°C to 42°C. This range in Fahrenheit scale is between 94°F to 108°F. To measure the body temperature, put the bulb of thermometer under the tongue inside mouth and hold it there for some time and then take it out. Now see the mercury level and note the reading.
RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat-6

This thermometer contains a kink near the bulb which does not let the mercury level to drop or rise by itself. So, each time before taking the temperature it is held firmly in hand and a few jerks are given so that the level of mercury goes down.

Question 3.
Explain the transfer of heat by convection method with a diagram.
Answer:
Heat transfer by convection.

Experiment:
Take water in a pot. Place few crystals of potassium permanganate or 4 – 5 beads of the leaves in it and heat. Observe water in a pot carefully, We will sec that water rises above from the centre and lowered from here and there. Colourful currents are set in water. This happens because when the bottom of the pot is heated, the water molecules absorb heat and move upwards whereas the upper molecules are cool and move towards the bottom of pot. By this mechanism, the liquid molecules itself move form one place to another to transfer heat. This method of heat transfer is called convection of heat.
RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat-7

Question 4.
What are the applications of convection of heat in our daily life. Explain.
Answer:
The use of heat convection in Out daily life are as follows:
1. Ventilation:
Ventilation is the main use of convection in our daily life. Generally the air we exhale is hot and of low density compared to normal air. It rises up towards the roof and exits from ventilator near the ceiling and fresh air enters from doors and windows.

2. Chimney:
Smoke and gases which come out from house and factories being hot move upwards and exits through the chimney.

3. Oceanic currents:
Oceanic currents arise due to convection of heat, These are of two types: Hot water current and cold water current. Hot water currents flows from equatorial line to polar regions while cold water currents flow from polar region to equatorial line.

4. Air flow:
When a place has high temperature then its air becomes hot, rises up and expands. Because of this air pressure at that place is reduced. Then air starts to flow from cool place to hot place.

5. In summer, during monsoon air flows from the ocean for the same reason rainfall occurs.

RBSE Solutions for Class 7 Science Chapter 15 Temperature and Heat

Question 5.
When an object is irradiated with radiations, then what processes may occur?
Answer:
When heat radiations are radiated on a object, then following processes ma occur:

1. Reflection:
Some part of incident radiations arc reflected back by that object. Lustrous objects are good reflector. e.g. metals.

2. Absorption:
Some part of incident radiation energy is absorbed by the object. So object becomes hot and its temperature is increased. When we come in sun light, then we feel heat due to this reason

4. Transmission:
When radiations are strike over a transparent object. then transmission also occurs along with reflection and absorption.

Question 6.
What is radiation? How heat transfer occurs by radiation method?
Answer:
Radiation:
The heat radiated from sun reaches the earth as light through vacuum. The method in which heat transfer takes place without any medium is called radiation. Radiations are actually electro-magnetic waves which can move in vacuum with speed of light

Example:

  1. When we sit in front of a heater or stove, we receive heat by radiation.
  2. When a hot utensil is moved away from the flame, it cools down by transferring its heat to the environment by radiation.
  3. in the same way our bod also gives up heat to the environment and receives heat from it by radiation. This type of radiation occurs as waves are known as Infrared rays.

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