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प्रश्न
The teachers 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.
1) Name the device used to change the alternating voltage to a higher or lower value. State one cause for power dissipation in this device.
2) Explain with an example, how power loss is reduced if the energy is transmitted over long distances as an alternating current rather than a direct current.
3) Write two values each shown by the teachers and Geeta.
उत्तर
1) The transformer is a device used for changing the alternating voltage to a higher or lower value. Formation of eddy currents in the iron core of the transformer is one of the causes of power dissipation in this device.
2) In the long-distance transmission of energy through transmission lines, the power loss is mainly due to resistive loss. Now, this resistive loss is proportional to the square of current flowing through the lines i.e
`H prop I^2`
So, to minimise this loss, we need to minimise the current flowing in the wire. In case of dc, if we decrease the current flowing in the wire, though the power losses will decrease but simultaneous power received at the receiving station will also decrease. So, to achieve the required amount of power at the receiving station, we transmit the ac signal by stepping up the voltage with the lower value of current as ac gives the flexibility of stepping up or down the voltage. In this way, the power losses are reduced while maintaining the required amount of power at the receiving station.
3)
Two values shown by the teachers are:
- Believer of giving practical knowledge
- Good explainer
Two values shown by Geeta are:
- Curiosity of learning
- Good listener
APPEARS IN
संबंधित प्रश्न
A group of students while coming from the school noticed a box marked "Danger H.T. 2200 V" at a substation in the main street. They did not understand the utility of a such a high voltage, while they argued, the supply was only 220 V. They asked their teacher this question the next day. The teacher thought it to be an important question and therefore explained to the whole class.
Answer the following questions:
(i) What device is used to bring the high voltage down to low voltage of a.c. current and what is the principle of its working ?
(ii) Is it possible to use this device for bringing down the high dc voltage to the low voltage? Explain
(iii) Write the values displayed by the students and the teacher.
In a transformer, the frequency of A.C. voltage ______.
An ideal transformer has 100 turns in the primary and 250 turns in the secondary. The peak value of the AC is 28 V. The rms secondary voltage is nearest to ______
State the mathematical relation between a number of turns in the primary coil to a secondary coil in the step-up transformer.
State whether true or false. If false, correct the statement.
A transformer can step up direct current.
A step-down transformer reduces the supply voltage from 220 V to 11 V and increase the current from 6 A to 100 A. Then its efficiency is
Assertion: A transfonner cannot work on D.C. supply.
Reason: D.C. changes neither in magnitude nor in direction.
An iron rod of 0.2 cm2 cross-sectional area is subjected to a magnetising field of 1200 Am-1. If the susceptibility of iron is 599, then the magnetic flux produced is ______.
How do the input and output powers in a transformer compare? State the assumption made.
