KSEEB Solutions for Class 8 Science Chapter 15 Heat

KSEEB Solutions for Class 8 Science Chapter 15 Heat

Karnataka Board Class 8 Science Chapter 15 Heat

KSEEB Class 8 Science Chapter 15 Textual Questions & 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 heavier
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 hot or cold of a body is called ………
Answer:
heat/temperature

Question 2.
Temperature is expressed in degree ……………….
Answer:
degree centigrade/ Joule

Question 3.
Substances changes from liquid to a gas at a constant temperature, it is called …………
Answer:
condensation/boiling point

Question 4.
The temperature of boiling water in the Celsius scale of temperature is ……………
Answer:
C (100/373/212/32)

Question 5.
The SI unit of heat is ……………..
Answer:
Joule/ Celsius

III. State whether the following statement is true or False :

Question 1.
Liquid expands on heating
Answer:
True

Question 2.
The unit of heat and temperature are the same
Answer:
False

Question 3.
The bi-metal strip is used in Fan
Answer:
False

IV. Answer the following:

Question 1.
Distinguish between heat and temperature.
Answer:

1. 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.
2. Temperature :
   • Temperature is a measure of the degree of hot or cold. lt 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 is the same as the temperature of a tub of water.
   • It is the average kinetic energy of the molecules.
   • SI unit of temperature is Kelvin.

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

1. Increase in temperature
2. Thermal expansion
3. Change in the physical state
4. Change in 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 vigorously or rubbing a metal strip of an iron nail on a stone several times that is produced. There are examples to illustrate that heat can be generated from the energy of motion.

Question 4.
Describe an experiment to prove that solids expand on heating.
Answer:

Take two aluminum rods measuring 7 cm each to fix it to a stand with a paper-thin gap between the rods. Connect to a circuit. Heat the rod by a spirit lamp. Due to heat rods expand and touch each making the circuit closed. The bulb burns. This shows that solids expand due to heat.

Question 5.
Name two devices which use bimetallic strip.
Answer:
Thermal expansion of bimetallic strips used as a heat operated switch in the circuit of automatic equipment like an iron box, fire alarms, electric heater, etc. Some thermometers work on the principle of expansion of liquids In automobile engines useful work is done by the expansion of gases.

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

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

1. 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
2. Clinical 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 3 5°C to 42°C

Question 8.
Convert 100°F into Celsius and Kelvin scale of temperature.
Answer:
°C = 5/9 ( °F – 32 )
°C = 5/9 ( 100 –  32 )
°C = 5/9 × 68 = 340/9
°C = 39.77 = 40°
I = °C + 273
k = 40 + 273
k = 313

V . Match the following

Answer:

1. g
2. F
3. e
4. b

KSEEB Class 8 Science Chapter 15 Additional Questions & Answers

Question 1.
What is the temperature?
Answer:
An increase in average kinetic energy is called temperature.

Question 2.
What is meant by heat?
Answer:
The total kinetic energy of all the molecules in a substance is called heat. The SI unit of heat is Joule (J)

Question 3.
Mention the different effect produced by heat.
Answer:
The three effect produced by heat are

1. Increase in temperature
2. Thermal expansion
3. Change in physical state
4. Chemical change

Question 4.
In industries, metal pipelines are provided with loops at regular intervals. Why?
Answer:
In industries, hot water or molten liquid is transferred from one place to another through metal pipelines. The expansion and contraction might bend or break the pipe. To overcome this, these metal pipelines are provided with loops at regular intervals. The expansion of pipelines causes the size of the loop to increase slightly so the pipe does not break.

Question 5.
Mention the application of thermal expansion.
Answer:
Thermal expansion of bimetallic strips used as a heat operated switch in the circuit of automatic equipment like an iron box, fire alarms, electric heater etc. Some thermometers work on the principle of expansion of liquids In automobile engines useful work is done by the expansion of gases.

Question 6.
What is meant by anomalous expansion?
Answer:
The sensual property of water between 0°C to 4°C is called anomalous expansion i.e. water on cooling contracts up to 4°C and afterward it starts expanding till it freezes into ice at 0° C.

Question 7.
What is a thermometer?
Answer:
A thermometer is an instrument that measures the temperature of a system quantitatively.

Question 8.
Name different types of thermometers.
Answer:
There are three commonly used scales of temperature.

1. Celsius scale of temperature  °C
2. Fahrenheit scale of temperature °F
3. Kelvin scale of temperature  K

Question 9.
What do you mean by the 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 they have a different rate of exemption.

Question 10.
Draw a diagram of a Laboratory thermometer.
Answer:

Question 11.
Draw a diagram of a clinical thermometer.
Answer:

Question 12.
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 13.
What are the precautions to be taken while using a clinical thermometer?
Answer:

1. Precautions to be taken while using a clinical thermometer.
2. The thermometer should be washed before and after each use, preferably with an antiseptic solution.
3. Do not wash the thermometer with hot water.
4. Ensure that before use the mercury level is below 35° C.
5. Read the thermometer keeping the level of mercury along the line of sight.
6. Handle the thermometer with care, as you handle any glass articles.
7. Don’t hold the thermometer by the bulb while reading it.

Question 14.
Write an experiment to find the boiling point of water?
Answer:

Take about 50 Cm³ of water in a round -bottom flask and add a few fragments of broken porcelain. Heat the flask and note the temperature when boiling begins. Take readings every thirty seconds for five minutes, i.e., ten readings in all. and take the average as the boiling point.

Question 15.
Write the principle on which the thermometer is made.
Answer:
The thermometer is made on the property of the expansion of liquids on heating.

Question 16.
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 of the pressure crosses a certain limit. Due to the increases in the boiling points, the food substances are cooked within less time. Thus it saves energy.

Question 17.
Write an experiment to show the melting point of ice.
Answer:

Small ice cubes are taken in a Funnel. The funnel is fixed to a stand as shown in Figure. The thermometer bulb is kept in the funnel such that it is surrounded by ice cubes, keeps a glass bottle below the funnel. Ice begins to melt utilizing the heat of the surrounding air. Water thus formed drops out of the funnel. After 10 minutes note down the level of mercury in the thermometer and take the reading which shows the melting point of ice.

Question 18.
At what temperature do the Celsius and Fahrenheit thermometers show the same measurement? Prove it by calculation.
Answer:
Celsius scale has divisions between 0 and 100 while the Fahrenheit has divisions from 32 to 212 ie. 180 divisions. Since Celsius and Fahrenheit scales are equal.
C−0/100=F−32/180

C=5/9(F−32)

F=9/5C+32
∴ – 40° C = – 40°F
Give scientific reasons:

Question 19.
Ice melts when heated.
Answer:
Every solid substance melt at a definite temperature on heating. Hence, when we heat ice, the kinetic energy increases and they get separated and free to move.

Question 20.
Telephone wires sag during summer.
Answer:
The metallic wires tend to expand due to the heat of the summer, therefore they sag.

Question 21.
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 22.
Before use, the clinical thermometer is jerked.
Answer:
Before use, the clinical thermometer is jerked so that the mercury flows back into the bulb.

Question 23.
Water cannot be used as a liquid in a thermometer.
Answer:

1. The capillary tube required to be very long.
2. The increase in the water level cannot be easily visible.

Question 24.
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 soon.

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