Q: Question 9Celsius and Fahrenheit scales are related as :C5\dfrac{\text{C}}{5}5C = F - 329\dfrac{\text{F - 32}}{9}9F - 32C9\dfrac{\text{C}}{9}9C = F + 325\dfrac{\text{F + 32}}{5}5F + 325C = 9F + 32\dfrac{9}{\text{F + 32}}F + 329C5\dfrac{\text{C}}{5}5C = 9(F + 32)9(\text{F + 32})9(F + 32)

C5\dfrac{\text{C}}{5}5C = F - 329\dfrac{\text{F - 32}}{9}9F - 32Reason — The temperature on Celsius and Fahrenheit scales are realted as : C5\dfrac{\text{C}}{5}5C = F - 329\dfrac{\text{F - 32}}{9}9F - 32

Question 1

Question 1Describe an experiment to show that water has maximum density at 4°C. What important consequences follow from this peculiar property of water? Discuss the importance of this phenomenon in nature.

Accepted Answer

Hope's apparatus can be used for demonstrating that water has maximum density at 4°C. The apparatus consists of a tall metallic cylinder with two side openings P, near the top and Q near the bottom, fitted with thermometers T1 and T2 respectively.The central part of the cylinder is surrounded by a cylindrical trough containing a freezing mixture of ice and salt. The cylinder is filled with pure water at room temperature. The temperature recorded by both the thermometers is observed at regular intervals of time.Observations —Initially both thermometers T1 and T2 show same temperature (i.e., room temperature).First the temperature recorded by lower thermometer T2, starts decreasing and finally it becomes steady at 4°C, while the temperature recorded in upper thermometer T1 remains almost unchanged during this time.While the temperature recorded by lower thermometer T2 remains constant at 4°C, the upper thermometer T1 shows a continuous fall in temperature up to 0°C and then it also becomes steady.At this stage, the lower thermometer T2 shows the temperature 4°C at which water has the maximum density while the upper thermometer T1 shows the temperature of water and ice at 0°C.Important consequences that follow due to this peculiar property of water (i.e., anomalous expansion of water) are:It is responsible for bursting of water pipelines and destruction of crops during very cold nights.It helps in preserving aquatic life during very cold weather.In nature, during winter when the atmospheric temperature starts falling below 0°C, water at the surface of a pond initially at temperature above 4°C, begins to radiate heat to the atmosphere, so the temperature of water near the surface starts falling.When temperature of water at the surface falls below 4°C, water contracts and it's density increases and therefore, it sinks to the bottom.This continues till temperature of entire water reaches to 4°C. Now, further cooling of top layers below 4°C results in expansion of water and so it's density decreases.As a result, water does not sink further, but it remains on the surface. When the temperature of atmosphere falls below 0°C, water on the surface looses further heat to the atmosphere and gradually freezes into ice, but water below the ice layer remains at 4°C.The water layer just below the ice in contact with it will be at 0°C, as shown in figure. Since, ice is a poor conductor of heat, so ice now prevents the flow of heat from water of the pond to the atmosphere.Thus, temperature of water in contact with ice is at 0°C and that of layers below the ice gradually increases to 4°C. As a result, fish and other aquatic creatures remain alive in water of the pond (or lake), though water on the surface has frozen into ice. Nature thus protects the aquatic life during the winter season.

Question 2

Question 9Celsius and Fahrenheit scales are related as :C5\dfrac{	ext{C}}{5}5C​ = F - 329\dfrac{	ext{F - 32}}{9}9F - 32​C9\dfrac{	ext{C}}{9}9C​ = F + 325\dfrac{	ext{F + 32}}{5}5F + 32​5C = 9F + 32\dfrac{9}{	ext{F + 32}}F + 329​C5\dfrac{	ext{C}}{5}5C​ = 9(F + 32)9(	ext{F + 32})9(F + 32)

Accepted Answer

C5\dfrac{	ext{C}}{5}5C​ = F - 329\dfrac{	ext{F - 32}}{9}9F - 32​Reason — The temperature on Celsius and Fahrenheit scales are realted as : C5\dfrac{	ext{C}}{5}5C​ = F - 329\dfrac{	ext{F - 32}}{9}9F - 32​

Question 3

Question 13The change in volume of water when it is cooled from ...............°C to ...............°C is known as anomalous expansion of water :0,44,01,00,1

Accepted Answer

4,0Reason — The expansion of water when it is cooled from 4°C to 0°C, is known as anomalous expansion of water.

Question 4

Question 14The property of ice which prevents the flow of heat from water of a pond (or lake) to the atmosphere is :conductioninsulationlow specific heatnone of the above

Accepted Answer

insulationReason — Ice is a poor conductor of heat. Hence, it acts as an insulator and prevents the flow of heat from water of a pond (or lake) to the atmosphere.

Question 5

Question 15Identify the correct graph showing the variation in the volume of water with temperature :1.2.3.4.

Accepted Answer

Reason — The volume of water first decreases on heating it from 0°C to 4°C and then increases on further heating it from 4°C to 10°C. The volume of water is thus minimum at 4°C.

Question 6

Question 16Some quantity of water at 0°C is heated to 20°С. Identify the correct graph showing the variation of volume of water with temperature.

Accepted Answer

option 4Reason — As from 0°C to 4°C, water contracts so it's volume decreases as temperature increases, at 4°C water has maximum density and minimum volume and from 4°C to 20°C, water expands, i.e., volume increases as temperature increases.So, the correct graph should show a decrease in volume from 0°C to 4°C and then an increase in volume from 4°C to 20°C. This forms a "U" shaped curve with the minimum point at 4°C.

Question 7

Question 4State the volume changes observed when a given mass of water is heated from 0°C to 10°C. Sketch a temperature-volume graph to show the behavior.

Accepted Answer

The volume of water first decreases on heating it from 0°C to 4°C and then increases on further heating it from 4°C to 10°C. The volume of water is thus minimum at 4°C.Temperature-Volume graph showing the variation in volume of water from 0°C to 10°C is shown below:

Question 8

Question 6A given mass of water is cooled from 10°C to 0°C. State the volume changes observed. Represent these changes on a temperature-volume graph.

Accepted Answer

On cooling water from 10°C, the density of water first increases up to 4°C and then decreases on cooling further below 4°C to 0°C.Hence, the density of water is maximum at 4°C which is equal to 1 g cm-3 (or 1000 kg m-3 )Temperature-Volume graph showing these changes is given below:

Question 9

Question 2Describe the energy flow in an ecosystem.

Accepted Answer

The diagram below shows the energy flow in the ecosystem.The producers (photo-synthetic plants) synthesize organic substances by the process of photosynthesis. The chemical energy so stored in plants is called gross primary production. The producers themselves first use the synthesized organic substances in the process of respiration in which some energy is used in oxidation of organic substances. The rest of the energy, called the net primary production, is stored for the growth, development and important metabolic processes.Next the primary consumers (herbivores) obtain their food from the producers, so they obtain only a small part of energy from the producers and the rest is wasted in decay of producers. A small part of the energy obtained by the primary consumers is utilized in respiration and the remaining part is stored in them as food.Afterwards, a small part of the energy stored as food in the primary consumers is obtained by the secondary consumers (carnivores). They again make use of a part of the energy in respiration and rest is stored in them as food.By repeating the sequence, the tertiary consumers (carnivores) obtain energy as food from the secondary consumers and utilise a small part of it in respiration and remaining energy is wasted in their decay and decomposition.The energy flow in ecosystems is thus linear i.e., it moves in a fixed direction. At the end, the energy reaches to the degraded (or unuseful) state. It does not return to the sun to make the process cyclic.

Question 10

Question 3Show that the energy flow in an ecosystem is linear.

Accepted Answer

The diagram below shows the energy flow in the ecosystem.Plants being primary producers, absorb solar energy to prepare food. This food is then used up by primary consumers, so they obtain only a small part of energy from the producers and rest is wasted in decay of producers.Afterwards, a small part of energy stored as food in primary consumers is obtained by secondary consumers (carnivores). They again use a part of energy in respiration and rest is stored in them as food.Now, the tertiary consumers (carnivores) obtain energy as food from the secondary consumers and utilise a small part in respiration and rest is wasted in their decay and decomposition.The energy flow in ecosystems is thus linear i.e., it moves in a fixed direction. At the end, the energy reaches to the degraded (or unuseful) state. It does not return to the sun to make the process cyclic.

Question 11

Question 10Choose the correct statement(s):A. According to the first law of thermodynamics, when energy is put to work, a part of it is always converted to non-useful form such as heat, mainly due to friction and radiation.B.	According to the second law of thermodynamics, energy can be transformed from one form to another, but it can neither be created nor destroyed.Both (A) and (B)only (B)only (A)None of these

Accepted Answer

None of theseReason — The laws of thermodynamics are stated below:First law of thermodynamics (Law of conservation of energy) — Energy can be transformed from one form to another form, but it can neither be created nor destroyed.Second law of thermodynamics — When energy is put to work, a part of it is always converted in unuseful form mainly as heat, due to friction and radiation.

Question 12

Question 7What do you mean by degradation of energy? Explain it by taking two examples of your daily life.

Accepted Answer

The gradual decrease of useful energy due to radiation loss, friction, etc. is called degradation of energy.Examples of degradation of energy —In transmission of electricity from a power generating station, a lot of electrical energy is wasted in the form of heat energy in the line wires used for transmission.When we cook food over a fire, the major part of heat energy obtained from the fuel is radiated out in the atmosphere. This radiated energy is of no use to us. It is thus a degraded form of energy.

Question 13

Question 8What is wind energy? How is wind energy used to produce electricity? How much electric power is generated in India using wind energy?

Accepted Answer

The large mass of moving air is called wind. Due to motion, it has kinetic energy. The kinetic energy of wind is called wind energy.Wind energy is used in a wind generator to produce electricity by making use of a wind mill (or wind turbine) to drive a wind generator.The figure above shows the arrangement of a wind generator in which a small electric generator (or dynamo) is placed at the top of a pillar. The armature of the dynamo is connected to the shaft attached with the blades of a wind mill. When the blowing wind strikes the blades of the wind mill, the kinetic energy of wind changes into rotational kinetic energy of the blades.The rotation of blades of the turbine rotates the armature of the dynamo in the magnetic field between the pole pieces N and S of a strong magnet, thus an alternating e.m.f is produced between the terminals T1 and T2 and hence electric power is generated.The electric power generated by a single wind mill generator is small. So to generate a sufficient amount of electric power, a large number of such wind generators are arranged over a big area called a wind farm, and then the electric power generated by each generator is combined together for supply to the consumers.At present in India, we are generating more than 10,000 MW electric power by this technique in coastal areas of Gujarat and Tamil Nadu.

Question 14

Question 12In a hydroelectric plant :Water is converted to steam to turn turbines and produce electrical energy.Potential energy of stored water is converted into electrical energy.Kinetic energy of stored water is converted into electrical energy.All of the above.

Accepted Answer

Potential energy of stored water is converted into electrical energy.Reason — In a hydroelectric plant, water is stored at a height in a dam. When it flows down, its potential energy is converted into kinetic energy, which then drives turbines to produce electricity.

Question 15

Question 5What is (i) tidal, (ii) ocean and (iii) geothermal energy? Explain in brief.

Accepted Answer

(i) Tidal energy — the energy possessed by rising and falling water in tides is known as tidal energy.But this is not a major source of energy because of the following two reasons —The rise and fall of sea water during tides is not enough to generate electricity on a large scale.There are very few sites which are suitable for building tidal dams.(ii) Ocean — Water in oceans possesses energy in two forms:Ocean thermal energy — The energy available due to the difference in temperature of water at the surface and at deeper levels of ocean.Oceanic (or sea) waves energy — the kinetic energy possessed by fast moving oceanic (or sea) waves.(iii) Geothermal energy — The heat energy possessed by rocks inside the earth is called geothermal energy.It is harnessed to produce electricity. The rocks present at hot spots, heat the underground water and turn it into steam, which gets compressed at high pressure between the rocks.By drilling holes into the earth up to the hot spots, steam is extracted through pipes which is utilized to rotate the turbine connected to the armature of an electric generator to produce electricity.

Question 16

Question 11What is carbon tax? Who will pay it?

Accepted Answer

Since, industries emit carbon dioxide to a great extent, to check them, they must be asked to pay carbon tax.This tax can be calculated on the basis of carbon emission from the industry, number of employee hours and turn over of the industry.This will encourage the industry to use energy efficient offices and to avoid the travelling of it's employees by having tele-conferencing.

Heat and Energy

Exercise 6A Long Answer Type

Exercise 6A Multiple Choice Type

Exercise 6A Short Answer Type

Exercise 6B Long Answer Type

Exercise 6B Multiple Choice Type

Exercise 6C Long Answer Type

Exercise 6C Multiple Choice Type

Exercise 6C Short Answer Type

Exercise 6D Short Answer Type