Chapter 7 ELECTRICITY & MAGNETISM ( KEELEKTRIKAN)

7.1 Electrostatics (Elektostatik)•Electrostatics is the study of static electrical charges. ( Elektrostatik ialah kajian tentang cas elektrik statik)•Two types of electrical charges, positive (+) and negative (-). (Terdapat dua jenis cas iaitu positif (+) dan negatif ( - ).

•Static charges can be produced trough friction. ( Elektrik statik boleh dihasilkan melalui geseran)• When two objects are vigorously rubbed against each other, one object receives electrons and the other loses electrons.( Apabila dua objek digosok dengan kerap, satu objek menerima elektron dan satu lagi kehilangan elektron.)

•The object which receives electrons becomes negatively charged. ( Objek yang menerima elektron menjadi bercas negatif)•The object which loses electrons becomes positively charged. (Objek yg melepaskan elektron menjadi bercas positif)

•Materials which have an equal number of positive and negative charges are classified as neutral. ( Bahan-bahan yg mempunyai bilangan cas positif dan negatif yg sama dikelaskan sebagai neutral)

How to determine the electrical charges?? ( Bagaimanakah kita mengesan cas elektrik ?? )

Electroscope ( Elektroskop)

(Ceper logam)

(Elektroskop tidak bercas)

(Penebat)

(Daun emas)

(Bekas kaca)(plat kuprum)

Nothing happen to the gold leaf. ( Tiada perubahan berlaku pada daun emas)

(Elektroskop bercas)

(negatif cas)

(daun emas mencapah)

Gold leaf is deflected

Gold leaf is deflected. ( Daun emas mencapah)

I III II II II II

I

During rubbing, (semasa gosokan),•The polythene strip gains electrons and becomes negatively charged. ( Batang politena mendapat elektron dan bercas negatif. )•The cap is positively charged when the negatively charged rod is placed near to it. ( Ceper logam akan bercas positif apabila rod yang bercas negatif diletak hampir kepadanya.)•The gold leaf will DEFLECTED. ( daun emas akan MENCAPAH)

If two charged objects are held close…(Jika dua objek yg bercas digantung bersama…)

(Cas bertentangan saling menarik)

(Cas yang sama saling menolak)

• The attraction and repulsion effect of charged materials shows that a force exists between electric charges. This force is known as electrostatic force. ( Daya tarikan dan tolakan bahan yang bercas menunjukkan suatu daya wujud di antara cas elektrik. Daya ini dikenal sebagai daya elektrostatik)

7.2 Electricity

Sources of electrical energy ( Sumber tenaga elektrik):

• Dry cells, lead acid accumulator, merkury battery, nickel-cadmium battery, solar cell.( sel kering, akumulator asid plumbum, bateri merkuri, bateri nikel kadmium dan sel suria.)

Electric current (Arus elektrik)• The flow of elctrons produces an

electric current. ( Aliran elektron menghasilkan arus elektrik.)

• In an electrical circuit, ( dalam satu litar elektrik,)

a. Electrons flows from negative terminalpositive terminal of the battery. ( Elektron mengalir melalui terminal negatif terminal positif bateri.)

b. Current flows from positive terminalnegative terminal of the battery.

( Arus mengalir melalui terminal positif terminal negatif bateri.)

• For electrons to flow from one point to another, energy is required voltage

( Tenaga diperlukan untuk elektron mengalir dari satu titik ke titik yang lain voltan)

• Electric current is defined as the rate of flow of charge through a conductor. ( Arus elektrik didefinisikan sebagai kadar pengaliran cas melalui satu konduktor.)

• Some materials allow electric current to flow through them easily while others do not. ( Sesetengah bahan membenarkan arus elektrik mengalir melaluinya dengan mudah sementara yang lain tidak)

• The property of a material that prevents or resists the flow of electrons through the material is called resistance. ( Ciri bahan yg menghalang pengaliran elektron melalui bahan dikenal sebagai rintangan)

Van de Graaff

•Van de Graaff produces elctrical charges at high voltages on its dome. (menghasilkan cas-cas elektrik yang bervoltan tinggi pada kubahnya.) •The friction between the belt and the pulley produces the electrical charges. ( Geseran antara geseran antara tali sawat dengan takal menghasilkan cas elektrik)

•S.I Unit for electric current is ??? ( Apakah unit S.I bagi arus elektrik???

Ampere (A) Is measured using ammeter

Current(Arus) Voltan (volt) Resistance (rintangan)

Unit S.I Ampere (A) - -

Unit Ampere Volt Ohm( )

Symbol I V R

Measured by using (Alat pengukuran)

Galvanometer / Ammeter

Voltmeter Resistor

How does the device connected? (Cara alat dipasang)

Series (bersiri) Parallel ( selari) -

How do ammeter and voltmeter connected

Series(bersiri)

Parallel(selari)

Resistance (rintangan)Influenced by 4 factors( dipengaruhi oleh 4

faktor)a. Length (Panjang wayar)– The longer of the wire, the greater the

resistance( Semakin panjang wayar, semakin tinggi rintangan)

b. Diammeter– The bigger the diammeter of the wire, the

smaller is its resistance (Semakin besar diameter wayar, semakin rendah rintangan)

Resistance (rintangan)c. Material (Bahan)– Different materials have different resistance.

Tungsten gives a high resistance, while copper gives very little resistance. (Bahan yg berbeza mempunyai rintangan yang berbeza. Tungsten memberi rintangan yang tinggi manakala kuprum memberi rintangan yang rendah)

d. Temperature(suhu)– The higher the temperature of the wire, the

higher the resistance ( Semakin tinggi suhu wayar, semakin tinggi rintangan)

7.3 Ohm’s Law ( Hukum Ohm)

V

I R

Exercise

Find the missing value in the circuit.1) 2)

3)

4)

7.4 Concept of series and parallel circuit (Konsep litar bersiri dan selari)

Series circuit Parallel circuit

Pathway of current(perjalanan arus)

Only one pathway for current to flow( Satu sahaja perjalanan arus)

Current can move in more branches (Arus mengalir dalam cabang-cabang)

If one bulb is fused (Kalau satu mentol rosak)

All other bulbs cannot light(Semua mentol tidak bernyala)

All other bulbs can still light(Semua mentol lain masih bernyala)

Series circuit Parallel circuit

Advantages (kebaikan) 1)Higher current is easily obtained(Arus yg lebih tinggi dapat diperoleh dengan mudah)2)If one component breaks down the other component cannot work.(Kalau satu komponen rosak, komponen yang lain tidak berfungsi)

1)If one component in the circuit breaks down, the other component still can work. (Kalau satu komponen rosak, komponen yg lain masih dapat berfungsi)2) Each component can be controlled by its own switch(Setiap komponen dikawal oleh suis sendiri)3)All components are controlled by main switch.Semua komponen dikawal oleh suis utama4) More components can be added to increase the voltage. (banyak komponen yg boleh ditambahkan utk meningkatkan voltan)

Series circuit Parallel circuit

Current (arus) Same. (sama)

I = I1 = I2 = I3

Total current.

I = I1 + I2 + I3

Voltage (voltan) Total voltage. (Jumlah voltan)

V = V 1 + V2 + V3

Same (sama)

V = V1 = V2 = V3

Resistance(rintangan) Total resistance

R = R1 + R2 + R3

Formula:

7.5 Magnetism

• Today magnets are made of alloys of metals such as alnico ( an alloy of aluminium, nickel and cobalt.) (Magnet diperbuat daripada logam aloi alniko( sejenis aloi campuran aluminium, nikel dan kobalt)

• Is an effect shown by magnet. (merupakan satu kesan magnet)

• Magnetic field(Medan magnetik) – is the space around a magnet under the influence of the magnet. (kawasan sekitar magnet dan di bawah pengaruh magnet)

•A magnetic field consists of lines of magnetic force or magnetic field lines.( Medan elektrik mempunyai garisan medan elektrik)•The magnetic field lines do not cross each other because the magnetic field lines from the same pole repel each other. ( Garisan medan elektrik tidak merentasi antara satu sama lain kerana garisan medan elektrik dari hujung yang sama akan saling menolak)

•The magnetic field lines from opposite poles attract each other. ( Garisan medan magnet dari hujung yang berbeza akan saling menarik)•The magnetic field lines are said to begin from the north pole of a magnet and move to a south pole.(Garisan medan magnet bermula dari hujung utara ke hujung selatan)•The pattern formed by the magnetic field depends on : (Corak yang terbentuk oleh medan magnet bergantung kepada :a. Arrangement of the magnets( susunan magnet)b. The strength of the magnet. (kekuatan magnet)

• When two similar poles face each other their magnetic lines r_____ each other and form a space with no magnetic influence. The space is called neutral point. (Apabila dua hujung yg sama bertemu, garisan medan elektrik akan saling me_______ dan membentuk satu ruang yg tiada kesan magnet. Ruang ini dinamakan titik neutral)

7.5. 2 Electromagnetism

• Electromagnetism is the magnetic effect produced by a current in a conductor. ( keelektromagnetan ialah kesan magnet yg dihasilkan daripada arus elektrik yg mengalir melalui satu konduktor.)

Electricity

Electromagnet

• A wire carrying an electric current produces a magnetic field around it. ( satu dawai yang membawa arus elektrik menghasilkan medan magnet di sekitarnya. )

Diagram 7.5.2

• The magnetic effect is even greater if a soft iron core is placed inside the coil. (kesan magnet akan lebih kuat jika satu besi diletakan di dalam gegelung dawai)

• The piece of soft iron becomes an electromagneti ( Besi itu menjadi elektromagnet)

• An electromagnet is a magnet due to current passing through the coil around it. (Elektromagnet ialah magnet yg terdapat elektrik mengalir melalui gegelung dawai yg berada di sekitarnya.)

• An electromagnet loses its magnetism as soon as the current is switched off. (Elektromagnet akan kehilangan sifat magnetik semasa pengaliran arus dihentikan)

• An electromagnet has a north pole and south pole. ( Elektromagnet mempunyai kutub utara dan kutub selatan.)

• The polarity of the electromagnet depends on the direction of the current( Kutub elektromagnet bergantung kepada arah arus.)

• To determine the poles of an electromagnet: (Untuk menentukan kutub elektromagnet:

a. Look at the end of the electromagnet. ( lihat hujung elektromagnet)

b. If the current flows in an anticlockwise direction, that is a north pole. (kalau arus mengalir secara lawan putaran jam, maka hujung tersebut ialah kutub utara)

c. Clockwise == > south pole( putaran jam ==> kutub selatan) ***refer diagram7.5.2

• The strength of an electromagnet can be increased by( Kekuatan elektromagnet dapat ditingkatkan dengan) :

a. Increasing the current( tinggikan arus)b. Using more turns of wire round the iron core.

(Gunakan lilitan yg lebih pada gegelung dawai.)

c. Using soft iron as the core. ( gunakan besi lembut)

7.5.3 Magnetic field around a straight wire carrying a current. ( Medan elektrik

sekitar wayar yang membawa arus

Right Hand Grip Rule

7.5.3 Magnetic field around a straight wire carrying a current. ( Medan elektrik

sekitar wayar yang membawa arus