Basic Technology JS2: Transmission of Electricity at high frequency - xpino SCHOLARS

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Thursday, January 8, 2015

Basic Technology JS2: Transmission of Electricity at high frequency




Transmission of Electricity at high frequency
The term ‘high frequency’ refers to any radio frequency between 3 and 30 megahertz.
Transmission of electricity at high frequency refers to the periodic reversing of the direction of the electric current called AC (alternating current) as opposed to direct current which flows in one direction only. 
The electrons move at very high speed both back wards and forward (i.e. oscillating) in a circuit known as tank circuit or oscillating circuit. It consists of a capacitor and an inductor connected as show below.





The normal frequency found in homes operates at 60Hz.  Anything higher than 60Hz would be considered high frequency, but they are usually found in electronics applications. The electrons within the of a high frequency electrical circuit have peculiar behavior. When the switch is closed, current will flow from the battery to the capacitor and inductor which normally store energy. But if the circuit is opened, it would be observed that the energy already passed on to the circuit component will remain there indefinitely without any reduction. This current will continue to move from the capacitor to the inductor and back to the capacitor again.
The above explanation can be related to the radio system, which involves the radiation of waves into spaces from the point of generation, and their reception at another point. The diagram below illustrates the basic elements of radio communication or broadcasting in transmitting messages, speeches or music from one place to another by radio.



  




For a radio to function at all, it will consist of these principal elements:
1.      A microphone which is used to control the radio waves in accordance with the information to be transmitted;
2.      A radio transmitter that will generate the radio frequency waves;
3.      A transmitting serial to send out the waves into space;
4.      A receiving serial to come across a portion of the radiated radio waves;
5.      A radio receiver to select and amplify the desired transmitter signal and extract the information out of the radio waves;
6.      A loudspeaker to convert the information signals which are in the form of electric current back into sound, which will be a close replica of the original information sent out.

How aerials (radio waves) transmitted and received
The electrons in the ‘tank circuit’ oscillate at a high frequency. A transmitter sets up electromagnetic waves (i.e. radio waves), which are transmitted through space. The accelerated electric charges i.e. electrons, always radiate energy in the form of electromagnetic waves. The charges in the glass rod and capacitor will not radiate since they are static.
The radiated waves from the oscillating circuit, however, are extremely weak. In order to radiate these electromagnetic waves from the tank or receive them effectively ‘aerials’ are needed. For instance, when you visit ‘Voice of Nigeria’ transmitting office in Ebute, Ikorodu, Lagos, you will see many transmitting aerials in form of masts. These ones are necessary for the effective transmission of radio waves.
Similarly, a receiving aerial or antenna which is usually connected to a radio receiver or television set, will catch or intercept just a small portion of the transmitted electromagnetic wave energy and pass it to other point of the radio or television after which we can receive the replica of the original signal being sent.
Many transmitting aerials are spread over the country. We can comfortably say there are two types of aerials, namely: transmitting and receiving aerials.
However, the modern method of receiving television signals directly in our homes is via satellite. The satellite is located some 36,000km above the earth, beams television programmes to reception dishes (dstv) or external/indoor antennas (NTA).


Exercises:
1.      Explain the term ‘high frequency’.
2.      What does transmission of electricity at high frequency mean?
3.      Of what relevance electrons in transmission of electricity at high frequency?
4.      When can a frequency be termed as high?
5.      For a radio to function at all, mention the 6 principal elements it will consist of?
6.      What are the two types of aerials?

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