Heat: Measuring Temperature, Thermometers, Transformation of Heat

Heat, energy that is transferred from one body to another as the result of a difference in temperature. If two bodies at different temperatures are brought together, energy is transferred—i.e., heat flows—from the hotter body to the colder. The effect of this transfer of energy usually, but not always, is an increase in the temperature of the colder body and a decrease in the temperature of the hotter body.

Measuring Temperature

The measurement of temperature is a comparatively new concept. Early scientists understood the difference between “hot” and “cold,” but they had no method to quantify varying degrees of heat until the seventeenth century. In 1597, Italian astronomer Galileo Galilei invented a simple water thermoscope, a device that consisted of a long glass tube inverted in a sealed jar that contained both air and water. When the jar was heated, the air expanded and pushed the liquid up the tube. The water level in the tube could be compared at different temperatures to show relative changes as heat was added or removed. However, the thermoscope lacked an easy way to directly quantify temperature.

Several years later, the Italian physician and inventor Santorio Santorio improved Galileo’s design by adding a numerical scale to the thermoscope. These early thermoscopes led to the development of the fluid-filled thermometers commonly used today. Modern thermometers operate based on the tendency of some fluids to expand when heated. As the fluid inside a thermometer absorbs heat, it expands, occupying a greater volume and forcing the fluid level inside the tube to rise. When the fluid is cooled, it contracts, occupying a smaller volume and causing the fluid level to fall.

Temperature is a measure of the amount of heat energy possessed by an object Because temperature is a relative measurement, scales based on reference points must be used to accurately measure temperature. There are three main scales commonly used in the world today to measure temperature: the Fahrenheit (°F) scale, the Celsius (°C) scale, and the Kelvin (K) scale.

Thermometers

Thermometer is an instrument for measuring the temperature of a system. Temperature measurement is important to a wide range of activities, including manufacturing, scientific research, and medical practice.

The accurate measurement of temperature developed relatively recently in human history. The invention of the thermometer is generally credited to the Italian mathematician-physicist Galileo Galilei (1564–1642). In his instrument, built about 1592, the changing temperature of an inverted glass vessel produced an expansion or contraction of the air within it, which in turn changed the level of the liquid with which the vessel’s long, openmouthed neck was partially filled. This general principle was perfected in succeeding years by experimenting with liquids such as mercury and by providing a scale to measure the expansion and contraction brought about in such liquids by rising and falling temperatures.

By the early 18th century as many as 35 different temperature scales had been devised. The German physicist Daniel Gabriel Fahrenheit in 1700–30 produced accurate mercury thermometers calibrated to a standard scale that ranged from 32°, the melting point of ice, to 96° for body temperature. The unit of temperature (degree) on the Fahrenheit temperature scale is 1/180 of the difference between the boiling (212°) and freezing points of water. The first centigrade scale (made up of 100 degrees) is attributed to the Swedish astronomer Anders Celsius, who developed it in 1742. Celsius used 0° for the boiling point of water and 100° for the melting point of snow. This was later inverted to put 0° on the cold end and 100° on the hot end, and in that form it gained widespread use. It was known simply as the centigrade scale until in 1948 the name was changed to the Celsius temperature scale. In 1848 the British physicist William Thomson proposed a system that used the degree Celsius but was keyed to absolute zero (−273.15 °C); the unit of this scale is now known as the kelvin. The Rankine scale employs the Fahrenheit degree keyed to absolute zero (−459.67 °F).

Any substance that somehow changes with alterations in its temperature can be used as the basic component in a thermometer. Gas thermometers work best at very low temperatures. Liquid thermometers are the most common type in use. They are simple, inexpensive, long-lasting, and able to measure a wide temperature span. The liquid is almost always mercury, sealed in a glass tube with nitrogen gas making up the rest of the volume of the tube.

Electrical-resistance thermometers characteristically use platinum and operate on the principle that electrical resistance varies with changes in temperature. Thermocouples are among the most widely used industrial thermometers. They are composed of two wires made of different materials joined together at one end and connected to a voltage-measuring device at the other. A temperature difference between the two ends creates a voltage that can be measured and translated into a measure of the temperature of the junction end. The bimetallic strip constitutes one of the most trouble-free and durable thermometers. It is simply two strips of different metals bonded together and held at one end. When heated, the two strips expand at different rates, resulting in a bending effect that is used to measure the temperature change.

Transformation of Heat

Heat is transfered via solid material (conduction), liquids and gases (convection), and electromagnetical waves (radiation). Heat is usually transfered in a combination of these three types and seldomly occurs on its own. For example, the thermal Environment of a building is influenced by heat fluxes through the ground (conduction), and the building envelope (mostly convection and radiation).

Convection is heat flux through liquids and gases. Heat Flux Sensors can measure convective heat flux. Examples of convective heat flux are:

Feeling much colder when it is windy.
Feeling much colder in water of 25°C than in air of 25°C.
Sensing principle in heat flux based mass flow sensors.

Conduction is heat flux through solid materials. Heat Flux Sensors can measure conductive heat flux. Examples of conductive heat flux are:

Touching a hot cup of coffee
Thermal influences in precision instruments.
Measurement of heat output from chemical reactors.

Radiation is energy that comes from a source and travels through space and may be able to penetrate various materials. Light, radio, and microwaves are types of radiation that are called nonionizing. The kind of radiation discussed in this document is called ionizing radiation because it can produce charged particles (ions) in matter.,

Heat is a form of energy that is transferred from one object to another due to a difference in temperature. The amount of heat transferred is proportional to the difference in temperature and the mass of the objects. Heat can be transferred in three ways: conduction, convection, and radiation.

Conduction is the transfer of heat through direct contact between two objects. For example, when you touch a hot stove, the heat from the stove is transferred to your hand through conduction.

Convection is the transfer of heat through the movement of fluids. For example, when you boil water, the heat from the stove is transferred to the water through convection. The hot water rises to the top of the pot and the cold water sinks to the bottom, creating a current that circulates the heat throughout the pot.

Radiation is the transfer of heat through Electromagnetic Waves. For example, the sun radiates heat to the Earth through electromagnetic waves.

The amount of heat required to raise the temperature of a substance is called its specific heat. The specific heat of a substance is a measure of how much heat it takes to raise the temperature of one gram of the substance by one degree Celsius. The specific heat of water is 4.184 joules per gram per degree Celsius. This means that it takes 4.184 joules of heat to raise the temperature of one gram of water by one degree Celsius.

The heat capacity of a substance is the amount of heat required to raise the temperature of the entire substance by one degree Celsius. The heat capacity of a substance is equal to the product of its specific heat and its mass.

Latent heat is the heat that is absorbed or released by a substance during a change of state, such as melting, freezing, boiling, or condensation. The latent heat of fusion is the heat that is absorbed by a substance when it melts. The latent heat of vaporization is the heat that is absorbed by a substance when it vaporizes.

Enthalpy is a thermodynamic quantity that is equal to the internal energy of a system plus the product of the pressure and volume of the system. The enthalpy change of a process is equal to the heat absorbed or released by the system during the process, at constant pressure.

Entropy is a thermodynamic quantity that is a measure of the disorder of a system. The entropy of a system always increases over time, unless the system is in a state of equilibrium.

A heat engine is a device that converts heat energy into mechanical work. The most common type of heat engine is the internal combustion engine, which is used in cars and other vehicles.

A refrigerator is a device that removes heat from a space and transfers it to another space. The most common type of refrigerator is the vapor-compression refrigerator, which uses a refrigerant to absorb heat from the inside of the refrigerator and transfer it to the outside.

A heat pump is a device that transfers heat from one space to another. Heat pumps can be used to heat or cool a space. The most common type of heat pump is the air-source heat pump, which uses the outside air to heat or cool the inside of a building.

Thermodynamics is the branch of physics that deals with heat and its relation to other forms of energy. Thermodynamics is used to study the Properties of matter and energy, and to design and analyze heat engines and other devices.

Measuring Temperature

What is temperature?

Temperature is a measure of the Average kinetic energy of the particles in a substance.

What is a thermometer?

A thermometer is a device that measures temperature.

What are the different types of thermometers?

There are many different types of thermometers, including liquid-in-glass thermometers, digital thermometers, and infrared thermometers.

How do thermometers work?

Thermometers work by measuring the expansion or contraction of a substance in response to changes in temperature.

What is the difference between Celsius and Fahrenheit?

Celsius and Fahrenheit are two different temperature scales. Celsius is the most common temperature scale used in science, while Fahrenheit is the most common temperature scale used in the United States.

What is the boiling point of water?

The boiling point of water is 100 degrees Celsius or 212 degrees Fahrenheit.

What is the freezing point of water?

The freezing point of water is 0 degrees Celsius or 32 degrees Fahrenheit.

Thermometers

What are the different types of thermometers?

There are many different types of thermometers, including liquid-in-glass thermometers, digital thermometers, and infrared thermometers.

How do liquid-in-glass thermometers work?

Liquid-in-glass thermometers work by measuring the expansion or contraction of a liquid in response to changes in temperature. The liquid is typically mercury or alcohol, and it is contained in a glass tube. The tube is marked with a scale that indicates the temperature.

How do digital thermometers work?

Digital thermometers work by measuring the electrical resistance of a semiconductor material in response to changes in temperature. The semiconductor material is typically a thermistor, and it is contained in a small, handheld device. The device displays the temperature on a digital display.

How do infrared thermometers work?

Infrared thermometers work by measuring the infrared radiation emitted by an object. The infrared radiation is converted into an electrical signal, which is then displayed on a digital display. Infrared thermometers are often used to measure the temperature of objects that are difficult to reach, such as the temperature of a baby’s forehead.

Transformation of Heat

What is heat?

Heat is a form of energy that is transferred between two objects that are at different temperatures.

What are the different ways that heat can be transferred?

Heat can be transferred by conduction, convection, or radiation.

What is conduction?

Conduction is the transfer of heat through direct contact. For example, when you touch a hot stove, the heat from the stove is transferred to your hand through conduction.

What is convection?

Convection is the transfer of heat through the movement of fluids. For example, when you boil water, the heat from the stove is transferred to the water through convection. The hot water rises to the top of the pot, and the cold water sinks to the bottom. This creates a current that circulates the water and distributes the heat evenly.

What is radiation?

Radiation is the transfer of heat through electromagnetic waves. For example, the sun radiates heat to the Earth through electromagnetic waves.

What are some examples of heat transfer in everyday life?

Some examples of heat transfer in everyday life include:

When you cook food, the heat from the stove is transferred to the food through conduction.
When you take a shower, the hot water from the showerhead is transferred to your body through conduction.
When you turn on the air conditioner, the cold air from the air conditioner is transferred to your room through convection.
When you sit in front of a fire, the heat from the fire is transferred to your body through radiation.

Sure, here are some MCQs on heat without mentioning the topic “Heat: Measuring Temperature, Thermometers, Transformation of Heat”:

Which of the following is not a way to transfer heat?
(A) Conduction
(B) Convection
(C) Radiation
(D) Friction
Which of the following is the best way to measure the temperature of a liquid?
(A) A thermometer
(B) A scale
(C) A clock
(D) A ruler
When water boils, it changes from a liquid to a gas. This is an example of which of the following?
(A) Melting
(B) Freezing
(C) Condensation
(D) Evaporation
When ice melts, it changes from a solid to a liquid. This is an example of which of the following?
(A) Melting
(B) Freezing
(C) Condensation
(D) Evaporation
When water freezes, it changes from a liquid to a solid. This is an example of which of the following?
(A) Melting
(B) Freezing
(C) Condensation
(D) Evaporation
When water condenses, it changes from a gas to a liquid. This is an example of which of the following?
(A) Melting
(B) Freezing
(C) Condensation
(D) Evaporation
Which of the following is the best way to cool a hot object?
(A) Put it in the sun
(B) Put it in the freezer
(C) Put it in the shade
(D) Put it in water
Which of the following is the best way to warm a cold object?
(A) Put it in the sun
(B) Put it in the freezer
(C) Put it in the shade
(D) Put it in water
Which of the following is the best way to keep a hot object hot?
(A) Put it in the sun
(B) Put it in the freezer
(C) Put it in the shade
(D) Put it in water
Which of the following is the best way to keep a cold object cold?
(A) Put it in the sun
(B) Put it in the freezer
(C) Put it in the shade
(D) Put it in water