CBSE Class 12 Physics 2018 Delhi Set 1 Paper

Question : 23

Total: 26

SECTION -D

The teachers of Geeta's school took the students on a study trip to a power generating station, located nearly 200‌km 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 long distances as an alternating current rather than a direct current.
(c) Write two values each shown by the teachers and Geeta.

Solution:

(a) Name of device
One cause for power dissipation
(b) Reduction of power loss in long distance transmission
(c) Two values each displayed by teacher and Geeta
(a) Transformer
Cause of power dissipation
(i) Joule heating in the windings.
(ii) Leakage of magnetic flux between the coils.
(iii) Production of eddy currents in the core.
(iv) Energy loss due to hysteresis.
[Any one/ any other correct reason of power loss]
(b) ac voltage can be stepped up to high value, which reduces the current in the line during transmission, hence the power loss (I2R) is reduced considerably while such stepping up is not possible for direct current.
[Also accept if the student explains this through a relevant example.]
(c) Teacher: Concerned, caring, ready to share knowledge.
Geeta: Inquisitive, scientific temper, good listener, keen learner (any other two values for the teacher and Geeta)

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