Measurement of Temperature

Which Instrument is Used to Measure the Temperature?

 

  1. Temperature is a measure of the degree of hotness of an object.
  2. A hot object has a higher temperature than a cold object.
  3. When two objects are in thermal contact, heat energy is transferred from the object at the higher temperature to the object at the lower temperature.
    Measurement of Temperature
  4. Table shows a comparison between temperature and heat.
    TemperatureHeat
    Degree of hotness of an objectEnergy transferred from a hot object to a cold object.
    A base quantityA derived quantity
    SI unit is kelvin (K)SI unit is joule (J)
    A scalar quantityA scalar quantity
  5. Temperature is measured by a thermometer. The most commonly used thermometer is the liquid- in-glass thermometer.
  6. A liquid-in-glass thermometer consists of a capillary tube with a thin-walled bulb at one end. It usually contains a fixed mass of mercury or alcohol.
  7. When the temperature increases, the volume of the mercury increases.
  8. This causes the mercury to expand into the capillary tube. Therefore, the length of the mercury column increases as temperature increases.
  9. The change in the length of the mercury column is proportional to the change in the temperature.
  10. The laboratory liquid-in-glass thermometers use the Celsius scale.
  11. The Celsius scale is defined by two fixed points of temperature – the ice point and the steam point. Table gives the definition and values of the two fixed points.
    Fixed pointDefinitionValue
    Lower fixed point: Ice pointThe temperature of pure melting ice0°C
    Upper fixed point: Steam pointThe temperature of steam from water that is boiling under standard atmospheric pressure100°C
  12. The liquid-in-glass thermometer uses the concept of thermal equilibrium to measure temperature.
    (a) When a thermometer is placed into an object, energy is transferred between the thermometer and the object until thermal equilibrium occurs.
    (b) The temperature of the thermometer is now equal to the temperature of the object.
    (c) Therefore the reading of the thermometer is the temperature of the object.

Calibration of Thermometers

A new thermometer without a scale can be calibrated by placing the bulb in ice and then in steam, as shown in Figure.
Measurement of Temperature 1Step 1

  • Place the bulb into melting ice.
  • Wait until the mercury column stops moving.
  • There is now thermal equilibrium at 0°C.
  • Mark 0°C on the stem.

Step 2

  • Place the bulb into steam.
  • Wait until the mercury column stops moving.
  • There is now thermal equilibrium at 100°C
  • Mark 100°C on the stem.

Step 3

  • Divide the region between the 0°C mark and the 100°C mark into 100 equal divisions.
  • Label the scale of the thermometer from 0, 10, 20, …, to 100.
  • The thermometer is calibrated and ready to measure temperature.
  1. If the scale of the thermometer is not marked, the temperature of an object can be determined from the formula or calibration graph, as shown in Figure.
    Measurement of Temperature 2
  2. Lower temperatures can be measured by liquid- in-glass thermometers filled with alcohol, which freezes at -115°C and boils at 78°C. The alcohol used needs to be coloured.
  3. For extra low temperature up to -200°C, liquid pentane is used instead of alcohol.
  4. Water is not suitable for use in thermometers because
    (a) it freezes at 0°C,
    (b) it does not expand regularly.
  5. The sensitivity of a thermometer can be increased by:
    (a) Decreasing the diameter of the capillary tube in the stem. This will cause the mercury column to move through a longer distance in the tube as it expands.
    (b) Using a bulb with thinner walls. Heat energy can be transferred at a faster rate into the mercury. The thermometer will respond faster to changes in temperature.

Calibration of Thermometers Example Problems with Solutions

Example 1. Figure shows a thermometer being used to measure the temperature of some sand.
Measurement of Temperature 3What is the temperature of the sand?
Solution:
Measurement of Temperature 4

Example 2. Figure shows the calibration graph of a mercury thermometer.
Measurement of Temperature 5
What is the temperature, y ?
Solution:
Measurement of Temperature 6

What is meant by Sublimation and what are the Factors that Affect the Rate of Evaporation

What is Sublimation in chemistry

Sublimation : The changing of a solid directly into vapours on heating, and of vapours into solid on cooling, is known as sublimation.
Sublimation can be represented as:
What is meant by Sublimation and what are the Factors that Affect the Rate of Evaporation 1 The solid substance which undergoes sublimation is said to ‘sublime’. the solid obtained by cooling the vapours of the solid is called a ‘sublimate’.
What is meant by Sublimation and what are the Factors that Affect the Rate of Evaporation 2Ex.       When solid ammonium chloride is heated, it directly changes into ammonium chloride vapour. And when hot Ammonium chloride vapour is cooled, it directly changes into solid ammonium chloride. Ammonium chloride, Iodine, Camphor, Naphthalene and Anthracene.

Evaporation : The process of change of a liquid into vapour at any temperature below its boiling point is called evaporation.

Factors affecting evaporation :

  1. Temperature : Rate of evaporation increase with increase in temperature. This is because with the increase in temperature more number of particles get enough kinetic energy to go into the vapour state.
    Ex.       Drying of clothes take place rapidly in summer than in winter
  2. Surface Area : The rate of evaporation increases on increasing the surface area of the liquid
    Ex.       If the same liquid is kept in a test tube and in a china dish, then the liquid kept in the china dish will evaporate more rapidly : Because more of its surface area is exposed to air.
  3. Humidity : Humidity is the amount of water vapour present in air. Air around us cannot hold more than a definite quantity of water vapour at a given temperature. If the amount of water in air is already large i.e., humidity is more, the rate of evaporation decreases. Thus, the rate of evaporation increases with decrease in humidity in the atmosphere.
    Ex.       Drying of clothes on a humid day.
  4. Wind speed :   The rate of evaporation also increases with increase in speed of the wind. This is because with increase in speed of wind, the particles of water vapour move away with wind resulting decrease in the amount of vapour in the atmosphere.
    Ex.       Clothes dry faster on a windy day.

What is Temperature and Can Temperature be Measured Directly

What is Temperature and Can Temperature be Measured Directly

Temperature

The degree of ‘hotness’ or ‘coldness’ of a body or a place is called temperature.
One of the methods of measuring the degree of hotness and coldness is by the sense of touch. But our sense of touch can sometimes be misleading. Let us look at the following experiment to understand why!

Activity
Aim: To show that the terms ‘hot’ and ‘cold’ as we feel them are only relative terms
Materials needed: Three glasses, hot water (as hot as you can bear to dip your finger in), ice-cold water, and water at room temperature
Method:
1. Pour hot water, water at room temperature, and the ice-cold water into three separate glasses.
2. Keep the three glasses side by side on a table with the glass containing water at room temperature in the middle.
What is Temperature and Can Temperature be Measured Directly 1
3. Dip the index finger of one hand in the ice-cold water and that of the other hand in the hot water. Hold the fingers in the water for a minute.
4. Then dip both the index fingers into the water at room temperature.
Observation: You will find that to one finger, the water feels hot and to the other it feels cold. Conclusion: This is because the finger that was in ice-cold water has become cold, and when it was placed in the water at room temperature, it felt that the water was warm, relative to the earlier experience of ice-cold water. Similarly, the finger that was first in hot water will feel the water at room temperature to be relatively cold.

So, you see the terms ‘hot’ and ‘cold’ are only relative terms. There must always be a reference body with respect to which we can say a given body is hot or cold.
Therefore, it is important that we use an instrument, rather than our own judgement, to measure temperature.

Measurement of Temperature
We measure temperature with an instrument called the thermometer. All thermometers measure temperature by making use of some property of a substance that varies with temperature. One such property is the change in volume of a substance (expansion and contraction) with temperature.

Temperature Scales

Just as we use different units to measure length (inches, centimetres, etc.), we use different units to measure temperature. These different units are represented by different temperature scales.
Here is a simplified description of how a temperature scale is defined. Two reference temperatures are chosen and the difference between these two temperatures are further broken down into a certain number of divisions. Each division is called one degree.
The most commonly used reference temperatures are the melting point of ice and the boiling point of water.
The three commonly used scales are the Celsius, the Fahrenheit scales, and the Kelvin scale.

  1. Celsius Scale
    This scale is indicated by °C [read as degree Celsius (in honour of Anders Celsius) or degree centigrade]. On this scale, the melting point of ice is taken as 0°C and the boiling point of water, as 100°C. The difference between these two points is divided into 100 degrees.
  2. Fahrenheit Scale
    This scale is indicated by °F (read as degree Fahrenheit). On this scale, 32°F is taken as the melting point of ice and 212°F as the boiling point of water. The difference between these two points is divided into 180 degrees.What is Temperature and Can Temperature be Measured Directly 2

Conversion of Temperature

Conversion Formula
Two simple equations given below will help us to convert one temperature scale into another.
F = (C x \(\frac{9}{5}\)) + 32, and
C = \(\frac{5}{9}\) (F – 32), where F is for Fahrenheit and C is for Celsius.

What is Temperature and Can Temperature be Measured Directly 3

Fet us look at the following examples to understand the conversion properly.

Example 1: Convert 86°F to °C.
Solution: We know that
C = \(\frac{5}{9}\) (F – 32)
= \(\frac{5}{9}\) (86 – 32)
= \(\frac{5}{9}\) × 54
Therefore, 86°F = 30°

Example 2: The temperature during a hot day in Delhi was 45°C. Express this temperature in degree Fahrenheit.
Solution:
We know that F = (C x \(\frac{9}{5}\)) + 32
We are given that C = 45°C, therefore, the day temperature in degree Fahrenheit
= (45 x \(\frac{9}{5}\)) + 32°F = (81+ 32)°F = 113°F

Types of Thermometers

The substance that is generally used in a conventional thermometer is either mercury or alcohol. Based on this, there are two types of thermometers: mercury thermometer and alcohol thermometer.

Mercury Thermometer
In 1714, Gabriel Fahrenheit invented the first mercury thermometer.
Mercury is used in thermometers because of the following reasons:

  • Mercury remains in the liquid state for a wide range of temperatures. It melts at -38.87°C and boils only at 356.58°C.
  • It is relatively easy to see because of its silvery grey colour.
  • It does not stick to glass.
  • It has a fairly uniform rate of expansion for a wide range of temperatures.

Alcohol Thermometer
Thermometers using alcohol have some advantages over mercury thermometers.

  • Alcohol is cheaper and less harmful than mercury.
  • Alcohol thermometers can measure much lower temperatures (up to -115°C) than mercury. However, the main disadvantage is that alcohol thermometers cannot measure temperatures higher than 78°C, whereas mercury thermometers can measure much higher temperatures.

Reading a Conventional Thermometer
The thermometers we use in the laboratory are called laboratory thermometers and the ones used to check body temperature are called clinical thermometers.

A laboratory thermometer is shown in Figure. It consists of a thin glass tube which is sealed at one end and has a bulb at the other end. The bulb is generally filled with mercury or alcohol, depending on whether it is a mercury or an alcohol laboratory thermometer. Mercury appears as a silvery grey line and alcohol looks like a red line in the thermometer. To read the temperature on this thermometer, you just read the number on the scale at the tip of the red or silvery-grey line. Remember to mention the unit used (Celsius or Fahrenheit).

The range of temperatures which a laboratory thermometer can measure is from -10°C to 110°C.

What is Temperature and Can Temperature be Measured Directly 4
Types of Thermometer

A clinical thermometer is generally a mercury thermometer though digital thermometers are becoming quite popular.
There are two characteristic features of a clinical thermometer:

  • There is a little arrow (at 98.4 or 98.6°F) showing the normal body temperature. .
  • There is a constriction or ‘kink’ in the tube near the bulb. This kink has been made to ensure that the mercury in the thermometer does not contract (and flow back into the bulb) before the temperature has been read.

To read the body temperature of any person with a clinical thermometer, follow the steps given below:
What is Temperature and Can Temperature be Measured Directly 5
Here are some precautions that one must follow while handling a mercury clinical thermometer.

  • Wash the thermometer well and dip it in an antiseptic liquid before and after using it.
  • Be careful while using a thermometer. It can break easily. Remember, mercury is a toxic substance.

The temperature of our body is closely related to a physical quantity called ‘heat’ or ‘heat energy’ possessed by the body. Let us learn more about this physical quantity.

How is Climate differ from Weather

How is Climate differ from Weather

Weather tells us about the changes that take place in the atmosphere at a given place and time. Weather forecasts are given regularly on television and in the newspapers.
Terms like hot, cold, humid, rainy, cloudy, etc./are the factors that are generally mentioned in a weather forecast. The weather of a place can change within a very short span of time. For example, you could wake up to a very bright and sunny day, and end up with heavy rains in the afternoon.
In this chapter, you will learn about weather, climate, the factors they depend on, and how animals adapt to the climatic conditions of their natural habitats.

Weather and Climate
The state of the atmospheric conditions like temperature, humidity, rainfall, snow, cloud cover, wind, etc. at a given place and time is called the weather of the place at that time. Temperature, humidity, rainfall, snow, cloud cover, wind, etc. are called weather elements. The characteristic pattern of weather elements in a place over a period of time is called climate of the place.
Both weather and climate affect our lives in many ways. Our way of living, the clothes we wear, the crops we grow, the food we eat, and many other things depend on the weather, and subsequently, the climate of the place that we live in.
Weather forecast is a prediction of the weather conditions for a place over a short period of time like the next few days. In order to make weather forecasts, scientists need to monitor the weather elements every day.
A special thermometer called the maximum- minimum thermometer is used to measure the maximum and minimum temperatures in a day.
How is Climate differ from Weather 1The relative humidity of the air is measured by an instrument called a hygrometer. The amount of rainfall is measured by an instrument called the rain gauge.
Climate tells us what it is like in the place where we usually live. For example, if we say that in the month of June, we expect it to be mild in Bengaluru, humid in Kolkata, hot and dry in Rajasthan, cold in Ladakh, and rainy in Kerala, then we refer to the climate of that place.

Factors that affect the climate of the Earth
The climate of the Earth has not remained the same through the ages. There have been periods when it has been extremely cold, as in the Ice Ages, when large areas of the Earth’s surface were covered with ice.
With the advance in science and technology and powerful computers, scientists are now able to simulate the Earth’s climate using a simplified model and study how various factors affect it. The study of climate is fast emerging to be a very exciting and challenging field of science.

Climate of the Earth as a Whole
Some of the factors that affect the climate of planet Earth as a whole are: the distance from the Sun and the Earth’s tilt.

1. Distance from the Sun
If you move closer to a lit stove you will feel warmer than when you are away from it. Similarly, the planet closest to the Sun is much hotter than the planet farther away from it. This is because the Sun is like a hot ball of fire.
The distance of the Earth from the Sun plays a major role in determining the temperature on the surface of the Earth and therefore its climate.

2. Earth’s Tilt
The Earth rotates about its axis (which is an imaginary line joining the North Pole and the South Pole).
How is Climate differ from Weather 2

The axis about which the Earth rotates, around the Sun, is at an angle with the plane of its orbit around the Sun. The angle that the Earth’s axis of rotation makes with the direction perpendicular to the plane of the Earth’s orbit around the Sun is called angle of inclination. This is about 23.5°. Inclination would have been zero if the Earth’s axis was perpendicular to the plane of its orbit around the Sun. It is this tilt in the Earth’s axis as well as revolution of the Earth around the Sun that causes the occurrence of seasons on the Earth. From 21st March to 23rd September, the Northern hemisphere is closer to the Sun. So, it is hotter than the Southern hemisphere, which is farther away from the Sun. The reverse happens in the next half of the orbit.
How is Climate differ from Weather 3

Change of seasons on Earth

Sunrise and Sunset
The length of a day is given by the difference in the times of the sunrise and sunset. It is not the same throughout the year because the area of the Earth’s surface lit by the Sun varies due to the Earth’s tilt and its position in its orbit around the Sun. In the Northern hemisphere, the longest day of the year is around 22nd June and the shortest day is around 22nd December.

Activity
Aim: To plot a graph of changes in length of the day
Materials needed: A centimetre graph sheet, data from your local newspaper for at least ten days, a sharp pencil, and an eraser
Method:
1. Note the time of sunrise and sunset from the daily newspaper for ten consecutive days.
2. Find the difference in the times to get the duration of each day, i.e., day length.
3. On a graph sheet, plot the date on the x-axis and the day length on the y-axis.
Observation: A curved graph is obtained.
Conclusion: You will see that the length of a day changes.

Climate of a Place
On the Earth, the climate of a place depends on many factors such as distance from the equator (latitude), height above sea level, distance from the sea and mountains, and so on.

1. Distance from the Equator (Latitude)
Places closer to the equator are warmer than the places closer to the poles. For example, it is much warmer in India (on an average, not taking into account exceptions like the higher reaches of the Himalayas) than Greenland. This is because the Sun’s rays fall directly on the equator and at an angle on the poles.
How is Climate differ from Weather 4

Sun’s rays falling on Earth

2. Height Above Sea Level and Distance from the Sea and Mountains
Why do people visit hill stations during summer? They do so because hill stations have a cooler climate than the plains. The higher a place is, the cooler it is. The sea has a moderating influence on the climate of a place.
How is Climate differ from Weather 5The places near the coast, such as Mumbai, Chennai, and Kolkata, are neither too hot nor too cold. On the other hand, places far away from the sea tend to have extreme climates with very hot summer and very cold winter.
You would have also learned how the Coastal areas are neither hot nor cold.
Himalayas affect the climate of North
India. Mountains can change or even stop winds and also influence the rainfall in a place.

Weather of a Place
Weather of a place is described by the temperature and humidity of that place.
1. Temperature
The temperature on any day depends (among other factors) on the amount of sunlight received. It is generally cooler during the nights than in the day time. One of the main reasons for this is that during the day, the rays of the Sun heat up the Earth. Temperatures may be many degrees higher in urban areas than in rural areas because of various factors such as pollution, higher density of people and houses, less number of trees, etc.

Activity
Aim: To plot a graph of daily changes in temperature
Materials needed: A centimetre graph sheet, temperature data from your local newspaper for at least ten days, and red and blue pencils.
Method:
1. Note down the date and the maximum and minimum temperatures from the newspaper for ten days.
2. On a graph sheet, plot the date on the x-axis and the corresponding maximum temperatures on the y-axis.
3. Join these points with a red pencil to get the maximum temperature graph.
4. Repeat Step 2 for the minimum temperatures. Now join the points with the blue pencil to get the minimum temperature graph.
Observation: A curved graph is obtained.
Conclusion: You can see from the graph that the maximum and minimum temperatures change daily.

2. Humidity
The amount of water vapour present in the atmosphere determines humidity. A drier place will have lower humidity. Places near the sea coast, like Kolkata and Mumbai, generally have greater humidity than places far away from the sea, like Delhi and Uttar Pradesh. Humidity of a region is usually higher in the rainy season than during summer and winter.

What is an Abiotic Component

What is an Abiotic Component

Abiotic Components
The word ‘abiotic’ means ‘non-living’. Light, air, water, soil, and temperature are some examples of abiotic components of the environment. Even though these components are themselves non-living, they have an effect on the living organisms, i.e., the biotic components of the environment.

Light
Plants use light to prepare their food.

Temperature
Temperature is a measure that tells us how hot or cold something is. Earth is the only known planet that has a temperature suitable for life to exist. Even on Earth, the temperature is not uniform all around. It is very hot near the equator, while places near the poles are very cold. Temperature affects the distribution of plants and animals around the planet.

Animals whose body temperature changes with the outside temperature are called cold-blooded animals. Most reptiles, insects, and amphibians are cold-blooded. Animals whose body temperature does not change with the outside temperature are called warm-blooded animals. Most mammals and birds are warm-blooded.

Warm-blooded animals can survive in areas having extreme temperatures like the desert and the Arctic region. Here, cold-blooded animals would have difficulty in surviving. Polar bear is adapted to survive in the harsh temperatures of the Arctic.

What is an Abiotic Component 1
Polar Bear

Air
Oxygen and carbon dioxide present in air are very important for the survival of organisms. Both plants and animals need oxygen for respiration. Animals and human beings release carbon dioxide during respiration, which is used by green plants for photosynthesis. Carbon dioxide is also released by burning of fuels in vehicles and factories. Plants, in turn, release oxygen into the environment. Thus, green plants play a very important role in maintaining the balance of oxygen and carbon dioxide in the environment. Moving air or wind also helps in the reproduction of plants through pollination and dispersal of certain fruits and seeds.

What is an Abiotic Component 2
The balance of oxygen and carbon dioxide in atmosphere

Water
Water is very important for living organisms. Plants absorb water through their roots, which is then transported to different plant parts. Water is essential for carrying out photosynthesis in plants.
It also plays an important role in the human body. Blood, which transports substances within the human body, is largely composed of water. In fact, 70% of the human body consists of water.
Water dissolves vital gases like oxygen and carbon dioxide. This enables living beings to survive in water.

What is an Abiotic Component 3
Water is essential for living organisms

Soil
Soil is the uppermost layer of the Earth’s crust. It has four sub-layers – topsoil, subsoil, parent material, and the bedrock. It is in the topsoil that plants grow.
Soil is very rich in minerals like magnesium, potassium, and phosphorus. Without soil, there would be no plants and thus, no food for us. Plants grow well in loosely packed soil as it allows their roots to grow deeper and also makes it easier for them to absorb water and nutrients. This is why farmers plough their fields before sowing seeds.

What is an Abiotic Component 4
Sub layers of soil

Animals like earthworm and snail also make the soil loose by turning it.

Habitat
Thus in nature, biotic and abiotic components are closely interrelated. Biotic components (organisms) interact with one another too. A group of interdependent organisms that live in the same region and interact with one anotherform a biotic community. A biotic community includes plants, animals, and microorganisms.