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Thursday, July 16, 2009

SPM F.A.Q: National Grid Network

If you study based on SPM checklist subtopic 3.5 that i listed in previous post, u'll be having less problem answering SPM physics' questions. TAk percaya??

Lets analyse the following SPM year 2005:
Question 12:
(a) Most of our electrical energy comes from hydroelectric power stations and thermal power stations. These power stations are connected by cables to transmit electricity to users in industries, offices, schools and houses. This system is called the national grid network.

(i) State the transformations of energy in a hydroelectric power station. [1 mark]
(Refer checklist 2)


(ii) Explain briefly the importance of the national grid network system in distributing electrical energy to the users. [4 marks]
(refer checklist 5)

Answers:
i. Gravitational Potential Energy -->Kinetic Energy--> Electrical Energy
(to understand about energy transformation, u need to appreciate principle of conservation of energy)

ii. ( u can choose any 4 of these advantages)
  • It enables continuous supply of electricity to the end user.
  • If one of the station break down, the other network can still operate.
  • Overall cost of the transmission network can be reduced
  • Energy loss is minimised due to use of high voltage transmission
  • General maintenance can be done without any interruption of power suply in other area.

Lets analyse the following question:
Figure 12.1 shows how a model of an electric transmission system can be set up in a laboratory. The model consists of a power station that generates 12 V of alternating current (a.c) that transmits the electrical energy to the users using transmission wires and transformers P, Q and R. If the resistance of the transmission wires between transformers P and Q in the model at Figure 12.1 is 30ohm , calculate:

(i) the current that flows in the transmission wire,
***Why don't u try this on your own :)

(ii) the power loss due to the heating effect of the currect in the transmission wire.
(refer checklist no. 4 for a clue)
[5 marks]
Answer:
i. 0.8A
ii. 19.2 W

So my advice is, make sure u cover all the aspect that being asked in those checklist.

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