Distribution and Domestic Power Supply

Þ The vocal cords

The larynx contains two small bands of elastic tissues. They are called vocal cords. The opening between the vocal cords is called epiglottis. When we breath in or out, the glottis is open. This is the position of the production of voiceless sounds. e.g. /f/, /s/, /h/, etc are voiceless sounds in English. The sounds produced when the glottis comes together are called voiced sounds. So the main function of the vocal cords is to produce voiced and voiceless sounds.

Þ The soft palate

The soft palate is also called velum. It is the roof of the mouth. It separates the oral and nasal cavity. The last part of the soft palate is called uvula. When it is lowered, the nasal sounds (/m, n, ŋ/) are produced. When it is raised, the air passes out through the oral cavity and the oral sounds (/p, t, k, s, etc/) are produced.

Þ The tongue

The tongue is an important organ of speech. It has the greatest variety of movement. It is divided into four parts: the tip, the blade, the front and the back. The number of vowels is produced with the help of the tongue. Vowels differ from each other because of the position of the tongue.

Picture of the tongue

The tip of the tongue helps to produce /t, d, z, etc/. The blade of the tongue helps to produce /t∫, dÎ, ∫, etc/. The front of the tongue helps to produce palatal sound /j/ and the back of the tongue helps to produce /k, g/ sounds.

Þ The lips

The upper lip and lower lip help to produce bilabial sounds /p, b, m/. If they are held together, the sounds produced in that position are bilabial stops : / p, b/. If the lips are held together, they produce different vowels.

Þ The teeth

The teeth take part in the production of consonant sounds. The upper teeth only take part in the production of speech sounds. The lower teeth don't take part for the production of sounds. The sound produced with the help of the upper teeth are called dental sound (q, r)

Þ The alveolar ridge

The alveolar ridge is the part between the upper teeth and the hard palate. The sound produced with the tongue touching the alveolar ridge is called alveolar sounds, e.g. /s/, /t/, /d/, etc.

Producing different speech sounds depends on the movement of speech organs. It is essential to know the movement and the placement of each organ to produce particular sounds. The above descriptions and functions of the organ of speech help you to guide students to produce the consonants and vowels in a right way.

Distribution and Domestic Power Supply

Unlike DC, AC can be stepped up to a higher voltage. Because of Ohm's law (Voltage equals Current times Resistance), electrical energy losses are dependent on current flow, not on energy flow. By using transformers, the voltage of the power can be stepped up to a high voltage so that the power may be distributed over long distances at low currents and hence low losses due to the resistance of the conductor. The voltage can then be stepped down again so that it is safe for domestic supply.

Three-phase electrical generation is very common and is a more efficient use of conductors. Three-phase electricity distribution is common only in industrial premises and many industrial electric motors are designed for it. Three current waveforms are produced that are 120 degrees out of phase with each other. At the load end of the circuit the return legs of the three phase circuits can be coupled together at the neutral point, where the three currents sum to zero. This means that the currents can be carried using only three cables, rather than the six that would otherwise be needed. Three phase power is a kind of polyphase system.

In many situations only a single phase is needed to supply street lights or residential consumers. When distributing three-phase electric power, a fourth or neutral cable is run in the street distribution to provide a complete circuit to each house. Different houses in the street are placed on different phases of the supply so that the load is balanced, or spread evenly, across the three phases when a lot of consumers are connected. Thus the supply cable to each house usually only consists of a live and neutral conductor with possibly an earthed armoured sheath.In india there is a recent trend of providing a High Voltage line upto the last end of the residence & then stepping it down to avoid pilferage of the Energy. Although this method has certain advantages but it has potential dangers associated with it.

For safety, a third wire is often connected between the individual electrical appliances in the house and the main electric switchboard or fusebox. The third wire is known in Britain and most other English-speaking countries as the earth wire, whereas in America it is the ground wire. At the main switchboard the earth wire is connected to the neutral wire and also connected to an earth stake or other convenient earthing point (to Americans, the grounding point) such as a water pipe. In the event of a fault, the earth wire can carry enough current to blow a fuse and isolate the faulty circuit. The earth connection also means that the surrounding building is at the same voltage as the neutral point. The most common form of electrical shock occurs when a person accidentally forms a circuit between a live conductor and ground. A residual-current circuit breaker is designed to detect such a problem and break the circuit before electric shock causes death. As many parts of the neutral system are connected to the earth, balancing currents, known as earth currents, may flow between the generator and the consumer and other parts of the system, which are also earthed, to keep the neutral voltage at a safe level. This system of earthing the neutral point to balance the current flows for safety reasons is known as a multiple earth neutral system.

Date: 2014-12-29; view: 1309