KSEEB Solutions for Class 8 Science Chapter 15 Heat

Students can Download Science Chapter 15 Heat Questions and Answers, Notes Pdf, KSEEB Solutions for Class 8 Science helps you to revise the complete Karnataka State Board Syllabus and to clear all their doubts, score well in final exams.

Karnataka State Syllabus Class 8 Science Chapter 15 Heat

KSEEB Class 8 Science Heat Textbook Exercise Questions and Answers

I. Four alternatives are given to each of the following incomplete statements/questions. Choose the right answer.

Question 1.
When an object is heated, the molecules that make up the object ______________.
(a) begin to move faster
(b) lose energy
(c) become faster
(d) become lighter
Answer:
(a) begin to move faster

Question 2.
The temperature of a body is an indicator of ______________.
(a) The total energy of the molecules of an object
(b) The average energy of the molecules of an object
(c) The total velocity of the molecules of the object
(d) The average kinetic energy of the molecules of an object
Answer:
(d) The average kinetic energy of the molecules of an object

Question 3.
A and B are two objects. The temperature of A is greater than that of B. This means that ______________.
(a) The molecules of A move faster on an average than the molecules of B.
(b) The total energy of A is greater than the total energy of the molecules of B.
(c) The average potential energy of A is greater than the average potential energy of B.
(d) The heat content of A will always be greater than that of B.
Answer:
(a) The molecules of A move faster on an average than the molecules of B.

II. Fill in the blanks with suitable words

Question:
1. The degree of hotness of a body is called ______________. (heat/temperature)
2. Temperature is expressed in ______________. (degree centigrade/joule)
3. A substance changes from liquid to a gas at a constant temperature It is called ______________. (condensation/boiling point)
4. The Temperature of boiling water in the Celsius scale of temperature is ______________.0 C(100/373/212/32)
5. The SI unit of heat is ______________. (joule/Celsius)
Answer:
1. temperature,
2. degree centigrade,
3. boiling point,
4. 100° C,
5. Joule

III. State whether the following statements are true or false.

Question:
1. Liquids expand on heating.
2. The unit of heat and temperature are the same.
3. A bimetallic strip is used in fans.
Answer:
1. true,
2. false,
3. false.

IV. Answer the following:

Question 1.
Distinguish between heat and temperature.
Answer:
Heat:

• Heat is a form of energy.
• Heat energy depends upon the speed of the particles, the number of particles and size or mass and the [type of particles in an object.
• It is the sum of energies of all molecules.
• SI unit of heat is joule.

Temperature:

• Temperature is a measure of the degree of hot or cold. It is a number that is related to energy, but it is not energy itself.
• Temperature does not depend on the size or mass of an object.
• For example, the temperature of a small cup of water will be the same as the temperature of a tub of water from which it is taken out
• It is the average kinetic energy of the molecules.
• SI unit of temperature is Kelvin.

Question 2.
Mention the three different effects produced by heat.
Answer:
The three effects produced by heat are

• Increase in temperature
• Thermal expansion
• Change in the physical state
• Chemical change

Question 3.
Give one example to illustrate that heat can be generated from the energy of motion.
Answer:
If we rub our palms together vigorously or by rubbing a metal strip or an iron nail on a stone several times, heat is produced. These are examples to illustrate that heat can be generated from the energy of motion.

Question 4.
Describe an experiment to show the change in the state of heating
Answer:
Take two aluminium rods measuring 7 cm each. Fix them to a stand with a paper-thin gap between them. Connect them to a circuit. Heat the rods by a spirit lamp. Due to heat the rods expand and touch each closing the circuit. The bulb will burn. This shows that solids expand due to heat.

Question 5.
Name two devices which use a bimetallic strip.
Answer:
Bimetallic strips are used in the circuits of automatic equipment like iron ‘ box, fire alarms, electric heater, micro oven, refrigerators, incubators and air conditioners.

Question 6.
A thick glass tumbler often cracks when boiling water is poured into it. Why?
Answer:
If we pour boiling water in to thick glass tumbler, it cracks immediately due to fact that glass is a poor conductor of heat. When boiling water is poured into the glass tumbler, the inner surface of the glass becomes hot and expands. But the outer surface of the glass wall does not expand. This uneven expansion cracks the glass.

Question 7.
State the similarities and differences between the laboratory thermometer and the clinical thermometer.
Answer:
Similarities of laboratory thermometer and clinical thermometer. The laboratory and clinical thermometer are both used to measure temperature or temperature changes. They are made of glass with mercury. Both are made on the property of expansion of liquids on heating.

Differences between laboratory and clinical thermometers.
Laboratory thermometer:

• used to measure the temperature of any substance.
• has a long graduated capillary tube.
• The range of laboratory thermometer is 0° C to 100° C.

Chemical thermometer:

• used to measure the only temperature in humans or animals
• has a short capillary tube with a narrow constriction.
• The range of clinical thermometer is 35°C to 42°C.

Question 8.
Convert 100° F into Celsius and Kelvin scale of temperature.
Answer:
Equivalent

V. Match the following:
A – B
1) formation of ice bergs – a) Kelvin scale
2) rise of mercury level in a thermometer – b) sudden contraction
3) automatic electric iron – c) Celsius scale
4) cracking of a hot glass plate when touched by a cold object – d) boiling point, e) bimetal strip, f) thermal expansion, g) anomalous expansion of water
Answer:
1. g,
2. f,
3. e,
4. b.

KSEEB Class 8 Science Heat Additional Questions and Answers

I. Answer the following:

Question 1.
What is thermal expansion?
Answer:
The phenomenon of the increase in the size of a substance due to heating is called thermal expansion.

Question 2.
What is meant by anomalous expansion?
Answer:
The unusual property of water between 0°C to 4°C is called anomalous expansion, i.e, water on cooling contracts up to 4° C and afterwards it starts expanding till it freezes into ice at 0° C.

Question 3.
What is a thermometer?
Answer:
The thermometer is an instrument that measures the temperature of a system quantitatively.

Question 4.
What do you mean by Bimetallic strip thermometer?
Answer:
Bimetallic strip thermometers include two different metals that are bonded together and expand at different rates as they warm up. Often, long bimetallic strips are wound into a coil and used with a dial.

Question 5.
Mention the two special features of the clinical thermometer.
Answer:
The capillary has a narrow bend called constriction.
The range of clinical thermometer is between 35° C and 42° C.

Question 6.
What are the three commonly used scales of temperature?
Answer:

• Celsius scale of temperature °C
• Fahrenheit scale of temperature0 F
• Kelvin scale of temperature K

Question 7.
Write the principle on which the thermometer is made.
Answer:
The thermometer is made on the property of expansion of liquids on heating.

Question 8.
How does a pressure cooker work?
Answer:
As the pressure increases, the boiling point of water also increases. In the pressure cookers, the boiling point of water increases due to the pressure created by blocking of the steam by weight. The weight rises up and lets out the steam, if the pressure crosses a certain limit. Due to the increase in the boiling points the food substances are cooked in lesser time. Thus it saves fuel.

Question 9.
What are the specific temperatures on different scales of temperature for the following:
Answer:

1. The freezing point of pure water
2. The boiling point of pure water
3. The temperature of the human body

Question 10.
Prove that -40° C = -40° F
Answer:
convert – 40° C into °F
F = \(\frac{9}{5}\) x C° + 32
= \(\frac{9}{5}\) x 40 + 32
= 9 x -8 + 32
= -72 + 32 = -40° F
∴ -40° C = -40° F

II. Give scientific reasons for the following:

Question 1.
Ice melts when heated:
Answer:
Every solid substance melts at a definite temperature on heating. Hence, when we heat ice, the kinetic energy increases and the molecules get separated and are free to move.

Question 2.
Clinical thermometer should not be used to measure the temperature of boiling water:
Answer:
The range of a clinical thermometer is designed to measure human body temperature ie between 35°C and 42°c. The temperature of boiling water is 100°c and if the clinical thermometer is inserted there is no space for the mercury to expand further and it will break.

Question 3.
Telephone/electric wires sag during summer:
Answer:
The metallic wires tend to expand due to the heat of the summer, therefore they sag.

Question 4.
Pyrex glass or borosilicate glass vessels can be used in the oven.
Answer:
Pyrex or borosilicate glass vessels can be used in the oven since they have the least expansion due to heat.

Question 5.
Space is left between small stretches while making cemented roads:
Answer:
Space is left between small stretches while making cemented roads in order to avoid accidents due to the expansion.

Question 6.
Metal pipelines are provided with loops at regular intervals:
Answer:
The expansion and contraction might bend or break the pipe to overcome this, metal pipe lines are provided with loops at regular intervals.

Question 7.
Anomalous behaviour of water is a boon to aquatic animals:
Answer:
Water on cooling beyond 4° C, expands and freezes into ice at 0°C and floats. But water at lower level stays at 4° C and aquatic life can survive. Since the density of the ice is less it floats and acts as an insulator to maintain the temperature of liquid water.

Question 8.
Before use, the clinical thermometer is given jerks.
Answer:
Before use, the clinical thermometer is jerked so that the mercury flows back into the bulb.

Question 9.
The range of clinical thermometer is between 35° C and 42°C:
Answer:
Our normal body temperature does not fall below 35°C or even under high fever does not rise above 42° C. Hence the range of clinical thermometer is between 35°C and 42°C.

Question 10.
Do not wash the clinical thermometer with hot water;
Answer:
Hot water will be definitely at a temperature much higher than 42° c and will make the mercury to expand. Since there is no space for expansion, it will break. So clinical thermometer should not be washed with hot water.

Question 11.
Water cannot be used as a liquid in a thermometer:
Answer:

• The capillary tube required will have to be very long.
• The increase in the water level can not be easily read.

Question 12.
Kelvin scale of temperature is similar to the Celsius scale of temperature:
Answer:
Kelvin scale of temperature is similar to the Celsius scale of temperature as in both scales there is 100 graduation between MP and BP.

Question 13.
Common salt is added to ice:
Answer:
Common salt is added to ice in order to reduce the melting point so that ice will not melt immediately.

II. Fill in the blanks:

Question:
1. All matter is made up of _____________ and _____________.
2. The total kinetic energy of all the molecules in a substance is called _____________.
3. The S.l unit of heat is _____________.
4. Increase in average kinetic energy is called _____________.
5. Temperature does not depend on the _____________ of the substance.
6. S.l unit of temperature is _____________.
8. Celsius scale of temperature was earlier referred to as _____________ scale.
9. 1 Celsius degree is equal to _____________ Fahrenheit degrees.
10. Zero Kelvin corresponds to _____________ in Celsius scale.
11. The first person to invent the thermometer was _____________.
12. The thermometer used to measure the temperature of the day and night is _____________.
Answer:
1. atoms and molecules,
2. heat,
3. joule,
4. temperature,
5. mass,
6. Kelvin,
7. expands,
8. centigrade,
9. 33.8,
10. 273° C,
11. Galileo,
12. Maximum-Minimum Thermometer.

III. Choose the correct answer:

Question 1.
The liquid used in a lab thermometer
(a) Mercury
(b) water
(c) Alcohol
(d) oil
Answer:
(a) Mercury

Question 2.
Heat always flows from _____________.
(a) Higher to lower temperature
(b) Lower to a higher temperature
(c) Equal temperature
(d) either equal or lower to a higher temperature
Answer:
(a) Higher to lower temperature

Question 3.
To convert temperature °F into °C, the formula is
(a) F = \(\frac{5}{9}\) (°C-32), (
(b) \(\frac{\left(^{0} F-32\right) \times 5}{9}=^{0} C\)
(c) \(\frac{5}{9}\) C + 32
(d) F = \(\frac{5}{9}\) (°C – 32)
Answer:
(b) \(\frac{\left(^{0} F-32\right) \times 5}{9}=^{0} C\)

Question 4.
In a Fahrenheit scale, the difference between the upper and lower fixed point is degrees.
(a) 180
(b) 100
(c) 32
(d) 212
Answer:
(a) 180

Question 5.
The temperature depends on of the substance.
(a) mass
(b) volume
(c) density
(d) kinetic energy
Answer:
(d) kinetic energy

Question 6.
Water expands when heated and contracts when cooled at a temperature of
(a) 0°C
(b) 100°C
(c) 4°C
(d)OK
Answer:
(c) 4°C

Question 7.
The liquid used in thermometer to measure temperature below 38° C.
(a) water
(b) mercury
(c) oI
(d) alcohol
Answer:
(d) alcohol

IV. Draw’ a neat labelled diagram of
(a) laboratory thermometer

(b) clinical thermometer