TEMPERATURE AND HEAT

MEASUREMENT OF TEMPERATURE


Before learning how to measure temperature, let us learn what is temperature

Temperature is a relative measure, or indication of hotness or coldness. A hot utensil is said to have a high temperature, and ice cube to have a low temperature.


















A measure of temperature is obtained using a thermometer. ( A thermometer is a device that measures temperature using a variety of different principles)

1. About Digital Thermometers

2. Appliance Thermometers

3. Bimetallic-Coil Thermometers

4. Calibrating the Thermometers

5. Cooking Temperatures

6. Disposable Thermometers

7. Food Safety Temperature Guide

8. Instant-Read Bimetallic Coil Thermometers

9. Oven Cord Thermometers

10. Oven Safe Bimetallic Coil Thermometers

11. Oven Thermometers

12 Placing the Thermometer

13. Refrigerator and Freezer Thermometers

14. Thermistor Thermometers

15. Thermocouple Thermometers

16. Thermometer Fork

Many physical properties of materials change sufficiently with temperature to be used as the basis for constructing thermometers. The commonly used property is variation of the volume of a liquid with temperature. For example, a common thermometer (the liquid-in-glass type) with
which you are familiar. Mercury and alcohol are the liquids used in most liquid-in-glass
thermometers. Thermometers are calibrated so that a numerical value may be assigned to a given temperature.

For the definition of any standard scale, two fixed reference points are needed. Since all substances change dimensions with temperature, an absolute reference for expansion is not available. However, the necessary fixed points may be correlated to physical phenomena that always occur at the same temperature. The ice point and the steam point of water are two convenient fixed points and are known as the freezing and boiling points. These two points are the temperatures at which pure water freezes and boils under standard pressure. The two familiar temperature scales are the Fahrenheit temperature scale and the Celsius temperature scale. The ice and steam point have values 32 °F and 212 °F respectively, on the Fahrenheit scale and 0 °C and 100 °C on the Celsius scale. On the Fahrenheit scale, there are 180 equal intervals between two reference points, and on the celsius scale, there are 100.


'scale of temperature' A reference scale with respect to which the temperatures can be measured is known as 'scale of temperature'. Various scales of temperatures are in use. Important scales of temperature are:

• Celsius scale

• Fahrenheit scale

• Kelvin Scale

Lower and upper fixed point of temperature

To devise a scale of temperature, fixed reference points (temperature) are required, with respect to which all other temperatures are measured. For both Celsius and Fahrenheit Scales of temperatures, the fixed points are as follows:

Lower fixed point:

Melting point of pure ice at normal atmospheric pressure is regarded as the lower fixed point

DETECTION OF AMPLITUDE MODULATED WAVE

Let Us learn about intermediate frequency

First of all let us understand meaning of intermediate frequency (IF)

The transmitted message gets attenuated in propagating through the channel. The receiving antenna is therefore to be followed by an amplifier and a detector. In addition, to facilitate further processing, the carrier frequency is usually changed to a lower frequency by what is called an intermediate frequency (IF) stage preceding the detection. The detected signal may not be strong enough to be made use of and hence is required to be amplified.

A block diagram of a typical receiver is shown here (a)

Detection is the process of recovering the modulating signal from the modulated carrier wave. We just saw that the modulated carrier wave contains the frequencies ωc and ωc ± ωm. In order to obtain the original message signal m(t ) of angular frequency ωm

a simple method is shown in the form of a block diagram(b)The modulated signal of the form given in (a) is passed through a rectifier to produce the output shown in (b). This envelope of signal (b) is the message signal. In order to retrieve m(t ), the signal is passed through an envelope detector.

Let Us learn the reason for using intermediate frequency.

Intermediate frequencies are used for three general reasons.

First reason at very high frequencies, signal processing circuitry performs poorly. Active devices such as transistors cannot deliver much amplification (gain) without becoming unstable. Ordinary circuits using capacitors and inductors must be replaced with cumbersome high frequency techniques such as striplines and waveguides. So a high frequency signal is converted to a lower IF for processing.

A second reason to use an IF, in receivers that can be tuned to different stations, is to convert the various different frequencies of the stations to a common frequency for processing. It is difficult to build amplifiers, filters, and detectors that can be tuned to different frequencies, but easy to build tunable oscillators. Superheterodyne receivers tune in different stations simply by adjusting the frequency of the local oscillator on the input stage, and all processing after that is done at the same frequency, the IF. Without using an IF, all the complicated filters and detectors in a radio or television would have to be tuned in unison each time the station was changed, as was necessary in the early tuned radio frequency receivers.

Third reason for using an intermediate frequency is to improve frequency selectivity. In communications circuits a very common task is to separate out or extract signals or components of a signal that are close together in frequency. This is called filtering. Some examples are, picking up a radio station among several that are close in frequency, or extracting the chrominance subcarrier from a TV signal. With all known filtering techniques the filter's bandwidth increases proportionately with the frequency. So a narrower bandwidth and more selectivity can be achieved by converting the signal to a lower IF and performing the filtering at that frequency.

Our next topic we shall learn about Frequency Modulation.

Waves

Let Us learn about Sky waves

First of all let us learn what are waves

The wave is a physical phenomenon that is found in a variety of contexts. You undoubtedly know about ocean waves and have probably played with a stretched slinky toy, producing undulations which move rapidly along the slinky. Other examples of waves are sound, vibrations in solids, and light.

let us learn meaning of Ground wave, Sky waves and Space wave.

Ground wave is also called surface wave. a surface wave is a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. A surface wave can also be an electromagnetic wave guided by a refractive index gradient. In radio transmission, a ground wave is a surface wave that propagates close to the surface of the Earth.

sky wave, often called the ionospheric wave, is radiated in an upward direction and returned to Earth at some distant location because of refraction from the ionosphere. This form of propagation is relatively unaffected by the Earth's surface and can propagate signals over great distances. Usually the high frequency (hf) band is used for sky wave propagation. The following in-depth study of the ionosphere and its effect on sky waves will help you to better understand the nature of sky wave propagation.

Space waves A radio wave that follows two distinct paths from the transmitting antenna to the receiving antenna—one through the air directly to the receiving antenna, the other reflected from the ground to the receiving antenna. The primary path of the space wave is directly from the transmitting antenna to the receiving antenna. So, the receiving antenna must be located within the radio horizon of the transmitting antenna. Although space waves suffer little ground attenuation, they nevertheless are susceptible to fading. This is because space waves actually follow two paths of different lengths the receiving site and, therefore, may arrive in or out of phase. If these two component waves are received in phase, the result is a reinforced or stronger signal. Alternately, if they are received out of phase, they tend to cancel one another, which results in a weak or fading signal.

Television broadcast, microwave links and satellite communication are some examples of communication systems that use space wave mode of propagation.

Communication

Importance Of Communication System

What is communication?
Communication is the act of transmission of information. Every living
creature in the world experiences the need to impart or receive information
almost continuously with others in the surrounding world.

It also means exchange of ideas, thoughts and feeling using a media call Language.

every communication system has three essential elements. They are transmitter, medium/channel and receiver.



Some Major Milestones in the history of communication

Motion Of Rigid Bodies

What kind of motion can a rigid body have?

Let us try to explore this question by taking some examples of the motion of rigid bodies. Let us begin with a rectangular block sliding down an inclined plane without any sidewise that it does not have translational motion is to fix it along a straight line. The only possible motion of such a rigid body is rotation. The line along which the body is fixed is termed as its axis of rotation. If you look around, you will come across many examples of rotation about an axis, a ceiling fan, a potter’s wheel, a giant wheel in a fair, a merry-go-round and so on


Let us try to understand what rotation is, what characterises rotation. You may notice that in rotation of a rigid body about a fixed axis, every particle of the body moves in acircle, which lies in a plane perpendicular to the axis and has its centre on the axis.


Rotation about a fixed axis
A ceiling fan & A potter’s wheel



shows the rotational motion of a rigid body about a fixed axis (the z-axis of the frame of reference). Let P1 be a particle of the rigid body, arbitrarily chosen and at a distance r1 from fixed axis. The particle P1 describes a circle of radius r1 with its centre C1 on the fixed axis. The circle lies in a plane perpendicular to the axis. The figure also shows another particle P2 of the rigid body, P2 is at a distance r2 from the fixed axis. The particle P2 moves in a circle of radius r2 and with centre C2 on the axis. This circle, too, lies in a plane perpendicular to the axis. Note that the circles described by P1 and P2 may lie in
different planes; both these planes, however, are perpendicular to the fixed axis. For any particle on the axis like P3, r = 0. Any such
particle remains stationary while the body rotates. This is expected since the axis is fixed.

Thus The motion of a rigid body which is not pivoted or fixed in some way is either a pure translation or a combination of translation and rotation. The motion of a rigid body which is pivoted or fixed in some way is rotation.

Center Of Mass

physics description of center of mass

My blog will help you to learn about center of mass.

We shall first see what the center of mass of a system of particles is and then discuss its significance.

For simplicity we shall start with a two particle system. We shall take the line joining the two particles to be the x- axis.

Let the distances of the two particles be x1 and x2 respectively from some origin O. Let m1 and m2 be respectively the masses of the two particles. The centre of mass of the system is that point C which is at a distance X from O, where X is given by
The terms "center of mass" and "center of gravity" are used synonymously in a uniform gravity field to represent the unique point in an object or system which can be used to describe the system's response to external forces and torques. The concept of the center of mass is that of an average of the masses factored by their distances from a reference point. In one plane, that is like the balancing of a seesaw about a pivot point with respect to the torques produced.

SYSTEMS OF PARTICLES

Introduction On System Of Particles.

I am interested to give introduction on System Of Particles.

A system of particles means a group of particles inter-related. The equations for a system of particles can be readily used to develop those for a rigid body. One new but very important concept introduced with a system of particles is the center of mass.

The following quantities are covered in this section.

* Center of Mass
* Momentum
* Angular Momentum
* Kinetic Energy

For more help on these problems we can always refer sites like http://www.tutorvista.com/and http://www.s-cool.co.uk. I have used these sites for learning these topics and understanding the concept better.


Our next topic is introduction on center of mass.