Physics KSSM F5 Zen Notes by Cikgu Heery

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Heery’s Zen Notes

Physics KSSM F5 2021

Chapter 4:

ELECTROMAGNET

Physics KSSM F5 Zen Notes by Cikgu Heery

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A. FORCE ON A CONDUCTOR WITH CURRENT/

DAYA KE ATAS KONDUKTOR PEMBAWA ARUS

1. We MUST know on how to determine the direction of force on the conductor by

using Fleming’s Left Hand Rule

Kita WAJIB tahu cara menentukan arah daya ke atas konduktor dgn menggunakan

Petua Tangan Kiri Fleming

QUESTION EXAMPLE – determine the direction of force on the conductor below

/tentukan arah daya ke atas konduktor di bawah:

ANSWER: upward/ ke atas

Physics KSSM F5 Zen Notes by Cikgu Heery

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2. We also MUST know how to draw the catapult field/ Kita juga WAJIB tahu melukis

medan lastik:

QUESTION EXAMPLE – Draw catapult field & force direction/ lukiskan medan lastik

& arah daya

ANSWER:

SPM QUESTION: Here is a conductor with magnet. Determine the direction of force on it. Ini ialah konduktor dengan magnet. Tentukan arah daya ke atasnya

ANSWER: D

Use Right Hand Grip

Rule

Guna Petua

Genggaman Tangan

Kanan

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3. Application – direct current motor/ Aplikasi – motor arus terus

a. How to increase the rotation speed of motor?/ Cara meningkatkan kelajuan

putaran motor?

Increase current/ voltage or reduce resistance Tingkatkan arus/ voltan atau kurangkan rintangan

Use stronger magnet Guna magnet lebih kuat

Increase the number of wire turns in coil Tambahkan bilangan lilitan gegelung

b. Brushless motor & brushed motor/ Motor tanpa berus & motor berberus:

BRUSHLESS MOTOR MOTOR TANPA BERBERUS

BRUSHED MOTOR MOTOR BERBERUS

NO BFF – no brush, no friction, no fire sparks Tiada berus, tiada geseran, tiada percikan api

Got BFF – has brush, generate friction, generate fire sparks Ada berus, jana geseran, hasilkan percikan api

Magnet rotates, coil stationary Magnet putar, gegelung pegun

Coil rotates, magnet stationary Gegelung putar, magnet pegun

Use Fleming’s Left

Hand Rule to

determine the

direction of rotation

Guna Petua Tangan

Kiri Fleming utk

menentukan arah

putaran

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B. ELECTROMAGNETIC INDUCTION/ ARUHAN

ELEKTROMAGNET

1. Describing the induction/ Huraian aruhan:

a. Move conductor across the magnetic field (relative motion happens) Gerakkan konduktor merentas medan magnet (gerakan relatif berlaku)

b. We are changing or cutting the magnetic flux Kita mengubah atau memotong fluks magnet

c. This will generate induction electromotive force (emf) Ini menjana daya gerak elaktrik (dge) aruhan

d. Induction EMF will generate induction current DGE aruhan menjana arus aruhan

2. Faraday Law/ Hukum Faraday:

“The higher the rate of cutting flux magnet, the higher the magnitude of induction EMF”

“Makin tinggi kadar pemotongan fluks magnet, makin tinggi magnitud dge aruhan”

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3. To determine the direction of induction current, we use Fleming’s Right Hand

Rule

Utk menentukan arah arus aruhan, kita guna Petua Tangan Kanan Fleming

Faraday Law’s application – the faster we move wire, the higher the galvanometer

reading!

Aplikasi Hukum Faraday – makin laju kita gerakkan dawai, makin besar bacaaan

galvanometer!

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4. For solenoid, we use Lenz Law to determined the direction of induction current/

Utk solenoid, kita gunakan Hukum Lenz utk menentukan arah arus aruhan

When we insert magnet, solenoid will have same pole with inserting magnet Apabila kita masukkan magnet, solenoid akan mempunyai kutub sama dgn magnet yg masuk

When we pull out magnet, solenoid will have different pole Apabila kita tarik keluar magnet, solenoid akan mempunyai kutub berbeza

*Use Right Hand Grip Rule to determine the direction of current in solenoid/

Guna Petua Genggaman Tangan Kanan utk menentukan arah arus dlm solenoid

5. How to increase the galvanometer reading?/ Cara meningkatkan bacaan

galvanometer?

Move magnet faster Gerakkan magnet lebih pantas

Use stronger magnet Guna magnet lebih kuat

Increase the number of wire turns in solenoid Tambahkan bilangan lilitan solenoid

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6. Application – direct current (dc) generator & alternating current (ac)

generator/

Aplikasi – penjana arus terus (at) & penjana arus ulang alik (au)

DC GENERATOR PENJANA AT

AC GENERATOR PENJANA AU

Work principle: Move coil cut magnetic flux generate induction emf induction current Prinsip kerja: Gerakkan gegelung potong fluks magnet jana dge aruhan jana arus aruhan

Has one carbon brush Ada satu berus karbon

Has two carbon brush Ada dua berus karbon

Generate current in one direction Jana arus satu hala

Generate current in alternating direction Jana arus yg gerak ulang alik

5. How to increase the induction current?/ Cara meningkatkan arus aruhan?

Move coil faster Gerakkan gegelung lebih pantas

Use stronger magnet Guna magnet lebih kuat

Increase the number of wire turns in coil Tambahkan bilangan lilitan gegelung

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C. TRANSFORMER

1. Simple transformer structure/ Struktur transformer ringkas:

Revision/ Ulangkaji:

- Function: change voltage / Fungsi: ubah voltan - Use alternating current (ac) / Guna arus ulang-alik (au)

2. Transformer’s work principle/ Prinsip kerja transformer:

a. AC power source generates ac current in primary coil Penjana kuasa au hasilkan arus au dalam gegelung primer

b. This will generate changing magnetic flux in soft iron core. SIC binds magnetic flux from primary to secondary coil Ini akan menjana fluks magnet yg berubah-ubah dalam teras besi lembut. TBL memaut fluks magnet dari gegelung primer ke gegelung sekunder

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c. Changing magnetic flux will change the voltage in the secondary coil Fluks magnet yg berubah akan mengubah voltan dalam gegelung sekunder

3. Calculation/ Pengiraan:

a. Voltage calculation/ Pengiraan voltan:

Voltage in primary coil (pc) = Voltage in secondary coil (sc) Number of wire turns in pc Number of wire turns in sc

Vp = Vs Np Ns

b. Transformer efficiency/ Kecekapan transformer:

Efficiency = Output power x 100% Input power = VsIs x 100% VpIp

c. For efficient transformer… / Untuk transformer unggul…

Input power = Output power

VpIp VsIs

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QUESTION EXAMPLE:

a. Here is an example of transformer. Calculate the value of output voltage. Ini ialah contoh transformer. Kirakan nilai voltan output

Answer:

Vp = Vs Np Ns

240 = Vs

100 250

Vs = 600V

b. This is an example of efficient transformer. Calculate the output current Ini ialah contoh transformer unggul. Kirakan arus output

Power input = power output

200W= Is x Vs

200W = Is x 50V

Is = 4A

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4. How to reduce energy loss in transformer?

Cara mengurangkan kehilangan tenaga dalam transformer

METHOD

WHY?

a. Use thicker wire Guna wayar lebih tebal

To reduce resistance Utk mengurangkan rintangan

b. Use laminated soft iron core Guna teras besi lembut berlamina

To reduce eddy current Utk mengurangkan arus pusar

c.Use soft iron as core Guna besi lembut sebagai teras

To reduce histerisis Utk mengurangkan histerisis

d.Wrap the secondary coil over primary coil Lilitkan gegelung sekunder di atas gegelung primer

To prevent magnetic flux leakage Utk mencegah kebocoran fluks magnet

5. Use of eddy current in induction cooking/ Kegunaan arus pusar dalam dapur

aruhan

a. AC power source generate high-frequency ac Punca kuasa au hasilkan au berfrekuensi tinggi

b. This will generate changing magnetic flux Ini menjana fluks magnet yg berubah-ubah

c. This produces eddy current in the frying pan Ini menghasilkan arus pusar dalam kuali

d. Heat in generated in the pan for cooking Haba dihasilkan dalam kuali utk memasak

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6. Transmission & distribution system of electrical energy/ Sistem penghantaran &

pengagihan tenaga elektrik

a. Step-up transformer is used after the power station Transformer injak naik digunakan selepas stesen janakuasa

b. This is to increase voltage so to send electricity at faraway places using National Grid Network Ini utk meningkatkan voltan utk menghantar elektrik ke tempat jauh melalui Rangkaian Grid Nasional

c. After that, step-down transformers are used. Kemudian transformer injak turun digunakan

d. This is to reduce voltage according to building requirement Ini utk mengurangkan voltan mengikut keperluan bangunan

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