Tegangan dan Arus Induksi

Transcription

1 Induced Emf and Induced Current There are a number f ways a magnetic field can be used t generate an electric current. Tegangan dan Arus Induksi It is the changing field that rduces the current. Induced Emf and Induced Current Induced Emf and Induced Current An emf can be induced by changing the area f a cil in a cnstant magnetic field The current in the cil is called the induced current because it is brught abut by a changing magnetic field. Since a surce emf is always needed t rduce a current, the cil behaves as if it were a surce f emf. This emf is knwn as the induced emf. In each examle, bth an emf and a current are induced because the cil is art f a cmlete circuit. If the circuit were en, there wuld be n induced current, but there wuld be an induced emf. The henmena f rducing an induced emf with the aid f a magnetic field is called electrmagnetic inductin.

2 Mtinal Emf Mtinal Emf THE EMF IDUCED I A MOVIG CODUCTOR Each charge within the cnductr is mving and exeriences a magnetic frce F qvb Mtinal emf when v, B, and L are mutually erendicular E vbl The searated charges n the ends f the cnductr give rise t an induced emf, called a mtinal emf. Mtinal Emf Mtinal Emf Examle 1 Oerating a Light Bulb with Mtinal Emf Suse the rd is mving with a seed f 5.0m/s erendicular t a 0.80-T magnetic field. The rd has a length f 1.6 m and a negligible electrical resistance. The rails als have a negligible electrical resistance. The light bulb has a resistance f 96 hms. Find (a) the emf rduced by the rd and (b) the current induced in the circuit. (a) E vbl 5.0m s0.80 T1.6 m 6.4 V (b) E 6.4 V I A R 96

3 Mtinal Emf Mtinal Emf MOTIOAL EMF AD ELECTRICAL EERGY The directin f the frce in this figure wuld vilate the rincile f cnservatin f energy. In rder t kee the rd mving at cnstant velcity, the frce the hand exerts n the rd must balance the magnetic frce n the current: F hand F ILB Mtinal Emf Magnetic Flux Cncetual Examle 3 Cnservatin f Energy MOTIOAL EMF AD MAGETIC FLUX A cnducting rd is free t slide dwn between tw vertical cer tracks. There is n kinetic frictin between the rd and the tracks. Because the nly frce n the rd is its weight, it falls with an acceleratin equal t the acceleratin f gravity. Suse that a resistance cnnected between the ts f the tracks. (a) Des the rd nw fall with the acceleratin f gravity? (b) Hw des the rincile f cnservatin f energy aly? x x E vbl t t xl xl A A BL B t t t t B BA BA t t magnetic flux BA

4 Magnetic Flux Magnetic Flux GEERAL EXPRESSIO FOR MAGETIC FLUX BAcs E t t t Magnetic Flux Magnetic Flux GRAPHICAL ITERPRETATIO OF MAGETIC FLUX BAcs The magnetic flux is rrtinal t the number f field lines that ass thrugh a surface.

5 Faraday s Law f Electrmagnetic Inductin Faraday s Law f Electrmagnetic Inductin FARADAY S LAW OF ELECTROMAGETIC IDUCTIO The average emf induced in a cil f ls is E t t SI Unit f Induced Emf: vlt (V) t Examle 5 The Emf Induced by a Changing Magnetic Field A cil f wire cnsists f 20 turns each f which has an area f m 2. A magnetic field is erendicular t the surface. Initially, the magnitude f the magnetic field is T and 0.10s later, it has increased t T. Find the average emf induced in the cil during this time. BAcs B Acs E t t B B Acs t V m cs T T 0.10 s Faraday s Law f Electrmagnetic Inductin Lenz s Law Cncetual Examle 7 An Inductin Stve Tw ts f water are laced n an inductin stve at the same time. The stve itself is cl t the tuch. The water in the ferrmagnetic metal t is biling while that in the glass t is nt. Hw can such a cl stve bil water, and why isn t the water in the glass t biling? LEZ S LAW The induced emf resulting frm a changing magnetic flux has a larity that leads t an induced current whse directin is such that the induced magnetic field ses the riginal flux change.

6 Lenz s Law LEZ S LAW The induced emf resulting frm a changing magnetic flux has a larity that leads t an induced current whse directin is such that the induced magnetic field ses the riginal flux change. Lenz s Law Cncetual Examle 8 The Emf Prduced by a Mving Magnet A ermanent magnet is araching a l f wire. The external circuit cnsists f a resistance. Find the directin f the induced current and the larity f the induced emf. Reasning Strategy 1. Determine whether the magnetic flux that enetrates the cil is increasing r decreasing. 2. Find what the directin f the induced magnetic field must be s that it can se the change influx by adding r subtracting frm the riginal field. 3. Use RHR-2 t determine the directin f the induced current. Lenz s Law Alicatins f Electrmagnetic Inductin t the Rerductin f Sund Cncetual Examle 9 The Emf Prduced by a Mving Cer Ring. There is a cnstant magnetic field directed int the age in the shaded regin. The field is zer utside the shaded regin. A cer ring slides thrugh the regin. Fr each f the five sitins, determine whether an induced current exists and, if s, find its directin.

7 Alicatins f Electrmagnetic Inductin t the Rerductin f Sund Alicatins f Electrmagnetic Inductin t the Rerductin f Sund The Electric Generatr The Electric Generatr HOW A GEERATOR PRODUCES AD EMF E v BL BLvsin W v r 2

8 The Electric Generatr The Electric Generatr E Emf induced in a rtating lanar cil AB sint E sint E E sint 2 f The Electric Generatr THE ELECTRICAL EERGY DELIVERED BY A GEERATOR AD THE COUTERTORQUE The Electric Generatr The magnetic frce gives rise t a cuntertrque that ses the rtatinal mtin. When the generatr is delivering current, there is a magnetic frce acting n the cils.

9 The Electric Generatr THE BACK EMF GEERATED BY A ELECTRIC MOTOR When a mtr is erating, tw surces f emf are resent: (1) the alied emf V that rvides current t drive the mtr, and (2) the emf induced by the generatr-like actin f the rtating cil. The Electric Generatr Cnsistent with Lenz s law, the induced emf acts t se the alied emf and is called back emf. I V E R The Electric Generatr Examle 12 Oerating a Mtr The cil f an ac mtr has a resistance f 4.1 hms. The mtr is lugged int an utlet where the vltage is vlts (rms), and the cil devels a back emf f vlts (rms) when rtating at nrmal seed. The mtr is turning a wheel. Find (a) the current when the mtr first starts u and (b) the current when the mtr is erating at nrmal seed. (a) V E 120 V 0 V I 29 A R 4.1 Mutual Inductance and Self Inductance MUTUAL IDUCTACE The changing current in the rimary cil creates a changing magnetic flux thrugh the secndary cil, which leads t an induced emf in the secndary cil. The effect in called mutual inductin. (b) V E I R 120 V V 0.49 A 4.1 E t

10 Mutual Inductance and Self Inductance Mutual Inductance and Self Inductance SELF IDUCTACE Emf due t mutual inductin E s I M t mutual inductance SI Unit f mutual inductance: 1V s A 1H (Henry) The effect in which a changing current in a circuit induces and emf in the same circuit is referred t as self inductin. Mutual Inductance and Self Inductance Mutual Inductance and Self Inductance THE EERGY STORED I A IDUCTOR Energy stred in an inductr Energy 1 2 LI 2 I E L t self inductance Energy density Energy density 1 2 B 2 SI Unit f self inductance: 1V s A 1H (Henry)

11 Transfrmers Transfrmers A transfrmer is a device fr increasing r decreasing an ac vltage. E s s t E t Transfrmer equatin Vs V s Es E s Transfrmers Transfrmers I I s V V s s A transfrmer that stes u the vltage simultaneusly stes dwn the current, and a transfrmer that stes dwn the vltage stes u the current.