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Question:

The teacher of Geeta's school took the students on a study trip to a power generating station, located nearly 200 km away from the city. The teacher explained that electrical energy is transmitted over such a long distance to their city, in the form of alternating current (ac) raised to a high voltage. At the receiving end in the city, the voltage is reduced to operate the devices. As a result, the power loss is reduced. Geeta listened to the teacher and asked questions about how the ac is converted to a higher or lower voltage. (a) Name the device used to change the alternating voltage to a higher or lower value. State one cause for power dissipation in this device. (b) Explain with an example, how power loss is reduced if the energy is transmitted over a long distance as an alternating current rather than a direct current. (c) Write two values each shown by the teachers and Geeta.

Solution:

(a) The device which is used to change the alternating voltage to a higher or lower value is a Transformer.
Power dissipation in this device can occur due to eddy current loss
(b) (i) AC is easier to transmit over distance. By stepping the voltage up (and the current down) via a transformer, less power is lost through wire
(ii) AC also generates lower heat losses because it is only at its peak voltage for a fraction of each alternation of polarity and is also at 0 volts twice during each cycle. Thus it allows the wires to run cooler and waste less power as heat
(c) Teacher: Concerned, caring, ready to share knowledge.
Geeta: Inquisitive, scientific temper, Good listener, keen learner.