3.5 Transmission of Electricity

Subtopic 3.5 is the last topic in Electromagnet which covers the generation & transmission of electricity.This subtopichow transformer plays the role in our transmission network.

Here i list out theSPM checklist for this subtopic:

You must be able to do the following:

1. List the Sources of energy used to generate electricity.
e.g, nuclear power, hyro power, wind & etc

2. Then..Describe ways to generate electricity..
U need to describe details of the examples given in number 1.Descibe how the energy is transformed for each case. For example, describe how hydoelectric power can generate electricity. ..I mean u need to explain how water is used to rotate the turbine to drive the generators. (Its all in your books)

3. Describe the transmission of electricity?
This one is important. It has been asked in previous SPM paper. So make sure u understand the model of eletricty transmission system. In other words,please study about our national grid network.

Power Station--> Step up trnsformer-->Transmission cables(wires)-->SubStation-->

4. Describe the loss of electrical energy in the transmission cables
Please notice that there is loss of energy along the cables into heat. U can calculate power loss using this equation P=I^2R..please read further on this in yr reference book.

5. State the importance of National Grid Network?
U need to list the advantages of using this networksuch as increase in efficiency, easy to maintain and etc. U can easily find this facts in your book..all u need to do is take out your reference book & read it NOW! :)

6. Explain the importance of renewable energy?
Well..please read this as well..its just like doing your english essay :)
When petrol price gone up last year, everybody is making noise. So its your task to explain that its crucial for us to find sources of renewable energy.

Basically after u've gone though checklist..
the next important thing is to DO QUESTIONS!!

SPM Questions: Transformer

In previous post,I gave u some SPM checklist instead of detailed notes about transformer. The reason i did that is to let u to do some work & revise what had been asked from the checklist.
Another reason bcoz i hate to spoon feed my student...

Usually..SPM questions are designed from those checklist. You can find these checklist in your text books under the column called learning outcome. If u have covered & understood everything that being asked in the outcome,i'm sure u can grab at least a 'B' for physics. However to get an A.. u need to do lots of extra exercises for P1,P2 & P3.
I know some of u hate to refer yr txt book..but trust me, those outcomes are your guidance..

Here i want to disucss some SPM passed year questions about transformer.
In my previous checklist, i asked u to state & relate the equation of ideal transformer.If u really understand the equation for ideal transformer, u shoudnt having prblem answering these questions. However your undrstanding on electricity must be strong enough..
Lets check'em out..

1.
SPM 2004




The important keyword in this questions is 'ideal transformer'.So in the xm i strongly advice u to underline this keyword. For ideal transformer, the output power is equal to input power.Since the bulb is having the same rating voltage & power, so it will produce same brightness. Answer: B







2.
(b) Figure 4.2 shows a circuit consisting of a transformer, an ammeter and two light bulbs. The ammeter reading is 0.5 A and both bulbs light up with normal brightness.












(i) What is the output voltage of the transformer?
(ii) Calculate the efficiency of the transformer?

i) Answer=12V
Explaination:
The bulbs are arranged in parallel. So the voltage across the bulbs are the same i.e 12V. The voltage across the bulb represents the output voltage of the transformer.
Basically this questions wanna test your basic understanding about electric circuit.

(ii) Calculate the efficiency of the transformer.
Efficiency = (Pout / Pin) x 100

Total Pout=2(24) =48W
Pin = VI =240 ( 0.5)= 120W

Eff= (48) / 120) } x 100
= 40%

Basically this questions wanna test your basic understanding about electric circuit. Please make sure u understand the parallel & series circuit calculation..

SPM:Transformer

Transformer is another important subtopic u need to master under Electromagnet. It is frequently being asked in paper1 & paper 2 SPM.

SPM checklist:,
i. u must know how to describe the structure of transformer & its working principle

ii. then u must know the difference between step-up & step-down transformer

iii. u must know how to state equation of ideal transformer,
i.e Vs/Vp= Ns/Np as well as VpIp=VsIs

iv. Question can also ask u to describe & explain about the energy losses in transformer

v. Next, u must also know the ways to improve efficiency of a transformer.

vi. Finally..u must know to solve the calculations

After reading all those checklist, go & revise your reference book for important key points.
Here i include cool videos frm the net which had explained some important part of the above checklist.

SPM tips: Revise Effectively !

Hi guys..

We are now in month of July...your BIG day is getting inches wide. I'm sure most of u r busy doing revision..are'nt u :)??

For those who have revised systematically since form4, they should not be feeling any pressure by now. But if you have not, i believe only u can describe how's your feelings rite now :) However do not panic. By panicking & worrying too much, it will not do u any good.You are beyond control over the time that has passed, but you certainly can maximize your remaining time effectively. The following short tips are ways to help you to maximize your revision efficiently;

- Please bear in mind,it is the quality of your revision that counts, not the quantity. You must keep track of the productivity of your revision, not just how long you have been revising. How?? One way is by doing questions. Never do any revison whitout practising questions. SPM measures your ability to answer questions, not how long you've revised. You need to practise all type of questions, ie paper 1, paper 2 & paper 3. Try to learn from the given answers.The more you've done it, the easier it becomes.

- How to practise efficiently? You can Make your own lists of topic that u r weakest in. Then find topical questions frm yr exercise book and give it a try. If possible, pass trial & SPM questions is the best to begin with.

- Extract some of the answers in key points or mind map, then make it as your own note. Make your note neat & pleasant to read. You can save more precious time instead of reading the whole book and u can cover more questions in this way. BUT please understand the answer..again, dont simply memorize them.

- Another way to revise is by making summaries of everything as you read and revise. Then work with the summaries as you read. You must revise everything often, not just once. We human tend to forget easily coz in our life there's lots of distraction such as tv, games, sports & others..

- Work in short, sharp durations with breaks in between. This keeps your concentration in optimal level. Reward yourself within the interval. For example, get some ice cream in between revision, sounds nice rite ;)

- When exams is getting too close, spend more time polishing things you know. So make sure you get your mind clear about things u dont know by now. Otherwise do u think u can digest things u dont know wihtin a week b4 exam??

What i listed just now are some common tips discovered through my experience & from those who has been doing research in revision methodology. There are many other tips that could be mentioned here..but for me no point if i listed all the tips but none of u is applying it. May be some of u have already applied your own method. If it is working productively just continue with it.

At the end of the day, u must learn how to revise effectively rather than having hours of non productive revision. I really wish all of u can do well in your SPM..Its all in your hands!! Go & try your BEST!!

SPM Questions: Motors & Generators

As i mentioned before, to understand application of each physics subtopic is vital. Usually in SPM they'll ask u about this in section B & C , paper 2.
For example, let us analyse an SPM question taken from year 2006 about motors.
But as usual, those who created the question loved to confuse the students.

Take a look at the diagram below.
Lets discuss the 1st part..the question asked them
i. explain how AC motor can rotate

If we analyse the diagram, they gave a labeled diagram for an AC motor. If u notice, we hardly find notes on reference book or textbook about AC motor. (try & find it)But we have been given in details about the structure of AC generators. If the student tend to simply memorize, they might had been described the AC generator working principle instead of AC motors. I would advice in this case for u to underline the word motor as to make u alert of things that being asked.

Basically to answer the 1st part, u just simply describe details of the turning effect in dc motor and mention what happen if the current changed in direction from the AC supply. U can draw diagram to help u describing the principle.

Now on the 2ndpart:
The question asked the student to modify the device into DC motor & make it rotate faster.
Again.. i strongly advice u underline these words, "DC motor & rotate faster". So in your answer you must give points on both cases.
-First, u need to explain how u are going to convert it into DC motor
..here comes the importance of revising the application of each subtopic. If u never read about motors, u are having difficulties answering this question.
Moreover in this case they combine some concept in Electronics to change the AC to DC.

-Then, give points on how to make it rotate faster.... I'm not gonna give u the answer for this, coz u can find it in your reference book or cerdik's passed year's book. So apa tunggu lagi, bukak lah buku..pegi baca ;)

What i'm trying to emphasize here is, please dont take for granted of any applications in each subtopic. In this case, u really need to identify the differences between AC-DC motors &
AC-DC generators.
But dont simply memorize them, understand how they work.
Who knows, it might come out in your trial..








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