Thiết kế bài giảng vật lý nâng cao lớp 11 tập 1

Thiết kế bài giảng vật lý nâng cao lớp 11 tập 1 tài liệu, giáo án, bài giảng , luận văn, luận án, đồ án, bài tập lớn về...

TRAN THUY H A N G HA DUYEN TUNG

TRAN THUY H A N G - H A DUYfiN T O N G

THIET KE BAI QIANG

NANG CAO

NHA XUAT BAN H A N 6 I

Ldi NOI DAU

Thiet ke'bai giing Vit Ii 11 nang cao dugc vid't theo chudng trinh sach

giao khoa (SGK) mdi ban banh nSm 2006 - 2007 Sach gidi thidu mdt each thie't kd'bai giang Vat li nang cao theo tinh t h i n ddi mdi phuOng phap day - hgc, nham phat huy tinh tich cUc nhan thiic cua hgc sinh (HS)

V^" ndi dung : Sach bam sat n6i d u n g sach giao khoa Vat li 11 theo chuong trinh nang cao O mdi tid't^ sach chi ro muc tidu v^ kie'n thiic, ki nSng, cac cdng viec chua'n bi ciia giao vidn (GV) va HS, cac phirong tidn hd trO giang day c^n thie't, nham dam bao chd't lUdng tifng bai, ttoig tid't len ldp Ngoai ra sach cd mci rdng, bo sung thdm mdt sd' ndi dung lidn quan tdi bai hgc bang nhidu hoat ddng nhSm cung ca'p thdm tif lidu dd cac thiy, c6 giao tham khao vSn dung tuy theo dd'i tUOng HS titng dia phucfng

y% phuung phap day hoc : Sach duOc tridn khai theo h u 6 n g tich cUc

boa boat ddng cua HS, la'y ccf sof cua mdi boat ddng la nhiing vide lam cua

HS ducii su hu6ng dSn, phu h d p v6i dac trung mdn hgc n h u : thi nghidm, thao luan, thuc hanh, n h i m phat huy tinh ddc lap, tU giac cua HS DSc bidt, sach rat chii trgng khau thuc hanh trong tutig bai hgc, ddng thcfi ciing chi ro tiing hoat ddng cu thd cua GV va HS trong mdt tid'n trinh day hgc, coi day la bai hoat ddng cung nhau trong do ca HS va GV la chu thd'

Chung tdi hi vgng cud'n sach nay se la mdt cdng cu thid't thuc, gop p h i n

hd trd cac thiy, cd giao giang day mdn Vat Ii 11 trong vide nang cao hidu qua bai giang cua minh _

Cac tac g i a

- Di xuS^t dugc phuong an thi nghidm kidm tra du doan vd su nhidm didn do tidjp xdc

- Bie't dugc tac dung ciia didn nghidm vk cdch sii dung didn nghidm

-Hidu dugc khai nidm didn tich didm, hang sddidn mdi

- Bidt dugc phuong, chidu vk dd Idfn cua luc tuong tac giiJa cdc didn tich didm

trong chan khdng (dinh luat Cu-I6ng) v^ trong didn mdi, bidu didn dugc cac luc tuong tac do

- Van dung dugc cdng thiic tmh Iitc tuong tdc giffa cdc didn tich didm trong chan

khdng vk tt-ong didn mdi dd lam mdt s6 b^i tap don gidn

- Bidt sir dung quy tdc hinh binh hanh dd tim luc tdng hgp tac dungTdn mdt didn tfch didm

2 Vi ki nSng

- Quan sat thi nghidm bidu didn ciia gido vidn, tii kd't qua thf nghidm rut ra hidn tugng vat ll quan sat dugc

- Bidu didn dugc cac vectcf luc tdc dung ldn didn tich didm

- Giai dugc mdt s6 bai todn vd dd ldn ciia luc tucfng tdc gifia hai didn tich didm dat Uong chan khdng va trong mdi tru&ng didn mdi

B - C H U I N B I

Gido vien

- Chudn bi mdt didn nghidm (c6 thd tiit lam bang vo Ion, chai nhua v^ cdc vat lidu

don gian), thanh kim loai

- Chu^ bi phie'u hgc tap

Hpc sinh

- On lai cac kidn thiic da hgc b chucfng tiinh vat If ldp 7, 8 THCS vd su nhiem didn

do eg xat, cae loai dien tieh, luc tuong tac gifla cdc vat tich didn, luc, vecto luc, each bieu didn luc

in - THif T Kfi HOAT D O N G DAY HOC

Hoat ddng cua hoc sinh

Boat dong 1

Kiem tra, chudn bi dieu kien

xuat phat Dat van de

Suy n^hi cd nhan tim cau tra Icfi :

Co hai loai dien tfch la didn tfch

duong va didn tfch am Luc tucfng

tdc gifla chiing co thd la luc hiit

hoac luc dly

a) *-Q ©-^

Ca nhan nhan thiic dugc vdh dd

cua bai bgc

Trd giup cua giao vi§n

GV ndu cau hoi ki^m tra cac ki^n thflc

da hgc:

- K^ tdn cac loai didn tich ma cdc em da dugc hgc ? Luc tuong tac gifla chiing co dac didm gi ?

GV dung hinh ve cac loai dien tich va ydu cdu HS xdc dinh phuong chi^u ciia cac luc tuong tdc gifla cac didn tich do

nghidn ciiu vi ddldn ciia cdc luc tuong

tdc do

Boat ddng 2

Tim hieu sir nhidm dien cua cdc

vM

Cd nhan ti^p thu, ghi nhd

Suy nghT ca nhan tim cau tra Icri

HSl : Ngucfi ta eg xdt thanh thuy

tinh vdi lua thi thanh thuy tinh se

nhilm didn Mu6n bid't thanh thuy

tinh c6 nhidm didn hay khdng

ngucri ta dua no lai gin cac mlu

gidy vun di xem no co hiit cdc

mlu gidy vun khdng

HS2 : Cg xat thanh thuy tinh vdi

mdt vat bat ki (vai khd, lua, )

Nd'u sau cg xdt thanh thuy tinh co

kha ndng but cdc vat nhe (vun

gidy, mlu bdng, bdc, ) hoac lam

loe sdng bong den ciia but thtr didn

thi chihig to Uianb thuy tinh da

nhidm didn

HS3 : Co thi kidm tra tinh nhi^m

didn bang cdch cho tucfng tdc vdi

mdt vat nhidm didn khae

B 6 sung cdc kid'n thiic vd don vi didn tfch va didn tfch ciia electron

Thdng bdo : - Don vi didn tfch la culdng, kl hidu Id C

- Didn tich ciia electron c6 gid tri Uiydt dd'i la e = 1,6.10"'^C

GV ndu cau hoi ve vdn dd cin nghidn

ciiu :

- Bang each ndo c6 thd lam cho thanh thuy tinh nhidm didn ? Dd kidm tra xem thanh thuy tinh c6 dugc nhidm didn hay khdng ngufifi ta lam nhu th^ nao ?

GV nhdn xet cdc cau tra Idi

GV gidi thidu chid'c didn nghidm

— Dd kidm tra xem thanh thuy tinh c6 nhidm didn hay khdng ngucri ta con co mdt dung cu thf nghidm nfla co tdn ggi

la didn nghidm

Cd nhan tid'p thu, ghi nhd

Cd nhan quan sdt, thao ludn nhdm

dd tim ra nguydn tie hoat ddng

cua didn nghidm

HS thao ludn chung todn Idp

- Vi didn tich dugc truydn tfl vdt

bi nhidm didn d^n hai Id kim loai

ciia didn nghidm Idm cha hai Id

kim loai dd nhidm didn ciing ddu

vd dly nhau

- Diing mdt vat da dugc nhidm

didn cho tid'p xiic vdi vdt chua

dugc nhidm didn

HS thao ludn chung toan ldp

- Dimg mdt vdt da nhidm didn

trudc la thanh thuy tinh hoac

thanh kim loai Vdt cin nhidm didn

Phuang dn 1 : Thdng bdo

: Khi mOt vdt nhidm didn cham vdo num kim loai thi didn tich truydn d^n hai Id kim loai Do d6 hai la kim loai dly nhau

vd xoe ra Didn tich truydn cho hai Id cdng Idn thi gdc xoe cdng ldn

Phuang dn 2 : Nd'u cd didu kien GV cd

thd tid'n hdnh nhanh thi nghidm vdi dien nghidm dd HS tu nit ra nguydn tic boat ddng ciia didn nghidm

GV ndu cdu hoi vd vdn dd cin nghidn ciiu tidp theo

- 6 trdn ta da bid't mdt cdch nhidm didn cho vat bdng cdch cg xdt, cd thd Idm cho mdt vdt nhidm didn bdng cdch ndc nfla khdng?

GV neu cdu hdi ggi y

- Tai sao hai Id kim loai cua didn nghidm lai xofe ra ?

- Cd thd dp dung didu dd dd 1dm cho mdt vat nhidm didn dugc khdng ? N^u dugc phdi Idm thd' nao ?

GV ndu cdu hdi dd xudt phuong an tW

nghidm di kidm tra

- Thi^t k^ phuong an thf nghidm dd kidm tra du doan trdn ?

Ia mdt thanh kim loai khdc Di

kun tra xem thanh kim loai cd

nhidm didn hay khdng ta diing

didn nghidm

- Cd thd diing qud clu bang kim

loai trdn dien nghidm 1dm vdt cin

dugc nhidm didn Ta cho thanh

kim loai da nhidm didn d^n tid'p

xuc vdi qud clu cin dugc nhidm

dien va quan sdt xem hai Id kim

loai ciia didn nghidm cd xofe ra

khdng

HS quan sdt va nit ra ke't ludn

- HS bi dua vao tinh the' hSit ngd:

thanh kim loai chua tidp xiic vdi

qua clu tren didn nghidm thi qua

clu da nhidm didn

Cd nhan ti^p thu, ghi nhd

HS quan sat va rut ra ke't ludn

- Hai la kim loai ciia didn nghidm

xoe ra ndn qua clu da bi nhidm

GV tidii hanh thi nghidm kidm tra

- Dua tiir tii thanh kim loai da dugc nhidm didn ddn qua clu kim loai trdn didn nghidm (nhung chua tidp xdc), ddng thdi ydu clu HS tap trung quan sat

GV thdng bao cac khdi nidm hidn tugng hudng ling tmh didn vd su nhidm didn do hudng ling

- Dua thanh kim lom ra xa qua clu thi qua clu U-d vd trang thdi khdng bi nhidm didn Khi dd hai la kim loai ciia didn nghidm khdng xoe ra

GV dua thanh kun loai ra xa de cho HS quan sat xem cd dung nhu vdy khdng

GV tie'n hanh thi nghidm kidm U-a

- Cho thanh kim loai tidp xuc vdi qua clu U-en dien nghidm Ydu clu HS quan sdt dd nit ra kdt ludn

— Dua thanh kim loai ra xa qua

clu thi qua clu vln nhidm didn

Cd nhdn tid'p thu, ghi nhd

Boat dong 3

Nghien curu dinh luat Cu-16ng

HS thao luan chung toan ldp

- Cd the HS chi dua ra dugc du

doan : Dd ldn cua luc tucfng tac

ciia hai dien tfch phu thudc vao dd

Idn cua hai didn tfch (vi cd thd HS

dua vao hien tugng hai la kim loai

ciia didn nghidm xoe ra cang rdng

nd'u dien tfch truydn cho chiing

cang ldn)

Ca nhan tid'p thu, ghi nhd

- Dua thanh kim loai ra xa, ydu clu HS quan sat dd nit ra kd't ludn

GV khdi quat hod kid'n thdc :

- Cd ba cdch nhidm didn cho mdt vdt : nhidm didn do cg xat, nhidm didn do tie'p xiic va nhidm dien do hudng dng

Chii y : mdt vdt dugc nhidm didn cung

ggi la vat dugc tfch didn

GV ndu cdu h d i :

- Ta da bidt cdc didn tfch cilng diu thi dly nhau, cac didn tfch khac ddu thi hiit nhau Dd Idn cua cac luc tuong tac dd phu thudc vao nhflng yd'u td ndo vd phu thudc nhu the' nao vao cac yd'u td dd?

GV thdng b a o :

- Nha vat If hgc Cu-Idng da dung chid'c can xoln dd khao sat luc tuong tac gifla hai qua clu nhidm dien ed kfch thudc nhd so vdi khoang each gifla chiing (ngucri ta ggi cdc vdt nhidm dien cd kich thudc nhd la cac didn tfch didm) va t6ng kd't cac kd't qua thi nghidm cua minh Lhanh dinh ludt Cu-Idng

GV thdng bao ndi dung dinh luat ldng, chii y giai thfch eac dai lugng cd trong bieu thiic eua dinh luat

Cu-Ca nhan tu thu thap thdng tin vd

tra Idi cac cdu hdi ciia GV

Bidu thiic : F = k qiq2 Trong dd: r la khoang each gifla hai dien tich qi, q2

k = 9.10^1ahesdtild

Khi day muc nay GV cung cd thd cho

HS tu dgc SGK va kidm tra thdng tin ma

HS thu thap dugc bdng each dat ra cdc cdu hdi nhu : phat bieu ndi dung dinh luat Cu-Idng va vid't bieu thdc ciia dinh luat, giai thfch ro cac dai Iugng cd trong cdng thiic

Boat ddng 4

Tim hieu luc tirong tac cua cac

didn tich trong moi trudng didn

moi va xdy dung cong thiic xac

dinh luc Cu-I6ng dirdi dang

vecta,

Ca nhan tiep thu, ghi nhd

Ca nhdn tu thu thap thdng tin va

GV thdng bao:

- Thf nghidm chiing td rang, luc tuong tdc gifla cdc dien tich didm dat trong mdi trudng dien mdi ddng tfnh, chiia dly khdng gian xung quanh didn tfch, giam di s (epxilon) lln so vdi khi chung dugc dat trong chan khdng

F = k |qiq2|

£ chi phu thudc vao tinh chit ciia didn mdi ma khdng phu thudc ma dd Idn cac didn tfch va khoang each gifla cdc didn tich, ggi la hang sd didn mdi

Khi day muc nay GV cung cd the cho

HS tu dgc SGK va kidm tra thdng tin ma

HS thu thap dugc bang each dat ra cdc cdu hdi nhu : khi cac didn tfch didm dat trong dien mdi ddng tinh thi luc tuong

11

tra Idi cac cdu hdi eua GV

HS thao ludn chung toan Idp, ca

Cung co' bdi hgc va dinh hirdng

nhiem vu hgc tdp tiep theo

Hodn thanh bdi 1,2 SGK '

HS boat ddng cd nhdn, sau dd trao

ddi nhdm va dai dien nhdtn ldn

bdo cao ke't qua phi^u hgc tap

- Ggi F|2 vd ijj Id luc ma didn tfch q, tdc dung len dien tfch qj vd vecto dd dai

ve tir didn tfch qi ddn didn tfch qj, vid't bidu thlie toan bgc bidu didn mdi quan

hd gifla F12 va T^2 ?

- Ggi F21 ^^ Iv^c ma dien tieh qj tac dung len didn tfch qi, thi bidu thiic todn hgc nao bidu didn mdi quan hd gifla hai luc F2 vd F,2 ?

Hudng dan HS lam nhanh hai bai I, 2 SGK

GV ydu clu HS lam vide vdi phidu hgc tap, GV nhan xdt, danh gid bai lam ciia

HS (dai dien nhdm)

Hudng din hgc bai d nhd :

- Lam cac bai tap 3,4 SGK

- On lai cdc kieh thdc vd so luge cdu tao nguydn tii, chdl din didn, chd't each didn

da hgc d THCS

PHIEU HOC TAP Cau 1 Chgn phuong an dung

Dd ldn ciia luc tuong tac gifla hai didn tfch didm diing ydn trong khdng khi

Id F Nd'u tang khoang each dat hai didn tfch didm ldn gdp ddi thi luc tucmg tac ciia hai dien tfch didm :

A tdng ldn gdp ddi

B giam mot mia

C tang Idn gdp 4 lln

D giam di 4 lln

Cau 2 Hinh ve bdn bidu didn luc tuong tdc

-gifla hai didn tfch didm qj vd q2 Ke't

ludn nao dung Uong cae ke't ludn sau ^^^.-^^ q2

day?

A dien tfch qj va q2 ciing ddu

B didn tfch qi vd q2 trdi ddu

C dien tich qj va qj cd dd Idn bdng

nhau nhung trdi ddu

D dien tfch qj va q2 cd dd Idn bang

nhau

Cau 3 Cho hai dien tfch didm cd dien tfch qj =-q2 dat trong nudc each nhau 3cm

Luc tuong tac gifta chung bang 10"^N Tim dd ldn cdc dien tfch dd va bieu didn luc tuong tac gifla chung tren hinh ve

13

BAI2

THUYfiT fiLECTRON DINH LUAT BAO T O A N DifiN TICH

I - MUC TifiU

1 \ i kien thiic

- Nam dugc ndi dung thuydt electron

- Ap dung thuyd't dlectron dd giai thich ba hidn tugng nhidm didn,

- Phat bidu va hidu dugc dinh ludt bao todn dien tfch

- Hidu dugc su phan chia cac chit thanh hai loai la chd't din didn vd chit each didn chi cd tfnh tuong ddi Hidu dugc muc dfch thf nghiem chiing minh thiiy tinh khi d nhiet do thap la chit each didn, nhung khi d nhidt dd cao trd ndn din didn dugc

2 Vi kt nang

- Quan sat thf nghidm bidu didn cua giao vidn va nit ra kdt ludn vd hidn tugng vdt

If quan sat dugc

- Ap dung thuye't electron dd giai tbich cdc hien tugng nhidm didn

II ~ CHUAN BI

Gido vien

- Chuan hi thf nghiem chiing minh thuy tinh la chdt each didn d nhidt dd thdp,

nhung d nhiet do cao thuy tinh trd thanh din dien (GV co the tu che tao bd thi

nghiem chdng minh theo thiet kdhoqt ddng dqy hgc dudi ddy)

Ill - THIET K£ H O A T DONG DAY HOC

Hoat ddng cua hgc sinh

Boat dong 1

Kiem tra, chuan bi dieu kien xuat

phat Dat van de

Suy nghi ed nhdn tim cau tra Idi:

HS boat ddng ca nhan, sau dd trao

ddi nhdm va dai dien nhdm len bao

cao ke't qua

Cd thd HS chi trinh bdy dugc cac

hien tugng nhidm didn, vide giai

thfch cac hidn tugng gap be' tic

Ca nhan nhan thdc dugc vdh dd cin

nghien ciiu

Boat dong 2

Tim hieu thuye't electron

Ca nhdn tie'p thu, ghi nhd

HS thao luan chung toan ldp

- Ndu nguyen hi mat di mdt sd

electron thi tdng dai sd cac didn

tfch trong nguydn tii la mdt sd *

duong Ngugc lai, ndu nguyen tfl :

nhdn them mdt sd electron thi tdng i

dai sd cac didn tfch trong nguydn tur

la mot sd dm

Cd nhan tid'p thu, ghi nhd

T

Trd giiip cua giao vi^n

GV ndu cau hdi kidm tra kid'n thiic cu

- Trinh bay ndi dung so luge cd'u tao nguyen tii ?

- Neu va giai thfch cac each nhidm didn cho cae vat

DVD : Dd giai thfch dugc cac hien tugng nhidm dien chiing ta se dugc bo sung them kid'n thdc vd clu tao nguydn tir, phat trien thanh Thuyet electron va tim hidu Dinh ludt bao toan didn tfch

GV thdng bao 2 ndi dung diu ciia thuyd't dlectron

GV ndu cdu hdi dd HS xay dung ndi dung thd ba cua thuyd't dlectron

- Neu vi mdt If do nao dd, nguydn tii mdt di hoac nhan thdm mdt sd electron thi dien tfch cua nguyen tii se thay doi thd nao?

GV bd sung kid'n thdc :

- Khi tdng dai sd cac dien tfch trong nguydn tii la mdt sd duong, nd la mot ion duong Ngugc Iai, khi tdng dai sd cdc didn tfch trong nguydn tur la mdt sd

dm, nd la mot ion dm

15

Boat ddng 3

Giai thich ba hien tugng nhidm

dien

HS tid'p tuc boat ddng cd nhdn, sau

dd trao ddi nhdm va dai didn nhdm

ldn bao cao kd't qua

• Hidn tugng nhidm didn do cg xdt:

- Khi cg xdt thi dlectron se dich

chuydn tir thanh thuy tinh sang

mid'ng lua, do dd thanh thuy tinh

nhidm didn duong, mid'ng lua nhidm

didn dm

Ca nhdn tid'p thu, ghi nhd

- Lia4 y : khdi lugng ciia dlectron rit

nhd ndn dd linh ddng cua chung rSft ldn Vi vdy, do mot sd didu kidn nao

dd mdt sd electron cd thd di chuydn tir vat nay sang vat khac Khi dd vat trd thanh nhidm didn Vat nhidm didn dm

la vat thira dlecn-on, vdt nhidm didn duong la vdt thid'u dlectron

GV ydu clu HS Idm vide vdi phid'u hgc tapsd 1

GV cd thd ndu cdc cdu hdi ggi ^^:

- Thanh thiiy tinh cd mdt sd eiecU-on, khi cg xat vdi lua thi sd electron thay ddi thd'ndo?

- Khi dd, thanh thuy tinh se thiia hay thie'u dlectron ?

- Thanh thuy tinh nhidm didn gi ? Midhg lua nhidm didn gi ?

GV bd sung (neu cin) : Nd'u cd nhflng didm ti^p xiic gifla thuy tinh va lua thi

d nhihig diem tiep xuc dd cd mdt sd dlectron tfl thuy tinh di chuydn sang lua Khi thanh thuy tinh cg xdt vdi lua thi sd didm tiep xuc tang ldn rit Idn

Do dd sd electron di chuyen tii thuy tinh sang lua cung lang ldn Vi vdy thanh thiiy tinh nhidm didn duong, manh lua nhidm didn dm Thdi gian cg xat cang lau thi sd dlectron dich chuydn cang nhidu

• Hien tugng nhidm dien do tid'p

xuc :

- Khi eho thanh kim loai nhidm

didn am tid'p xiic vdi qua clu trung

hoa vd dien, thi mdt phdn eiecUon

thira d thanh kim loai truydn sang

qua clu Vi the' qua clu thiia

electron vd nhidm didn am

- Ngugc Iai, nd'u cho thanh kim loai

nhidm dien duong tidp xuc vdi qua

clu trung hod vd didn, thi mdt sd

electron d qua clu truydn sang

thanh kim loai Vi th^ qua clu thid'u

electron va nhidm didn duong

• Hien tugng nhidm dien do hudng

ling:

- Thanh kim loai trung hod vd dien

dat gin qua clu nhidm didn am, thi

cac electron tu do trong thanh kim

loai bi dly ra xa qua cau Do dd,

diu thanh gin qua clu thie'u

electron ndn nhidm dien dugng, cdn

diu kia nhidm didn am

Ca nhdn tiep thu kidn thdc

- Sd dlectron trong thanh kim loai

khdng thay ddi, chi thay ddi su

phan bd dlectron

Ca nhan tidp thu, ghi nhd

- Nhan xet ve su nhidm dien cua thanh kim loai nhidm didn am va qua clu ming hoa vd dien sau khi da cho chiing tid'p xiic vdi nhau ?

- Khi tie'p xuc, electron se dich chuydn nhu the' nao ?

- Giai thfch tuong tu vdi trudng hgp thanh kim loai ban diu nhidm dien

duong?

- Electron tu do trong thanh kim loai

se chiu luc tac dung luc nao tdc dung ?

- Luc dd cd chidu nhu the' nao khi thanh kim loai dat gin qua clu nhidm didn dm ?

Thdng bao : dlectron se dich chuydn ngugc Iai nd'u thanh kim loai ddt gin qua clu nhidm didn ducfng Do dd, diu thanh gin qua clu nhidm didn dm, diu kia nhidm didn ducfng

- ^flidn xet vd su thay ddi sd electron ciia thanh kim loai sau khi dat gin qua clu nhidm didn am ?

GV thd che'hoa kidn thdc : Vay thuc chit cua su nhidm dien do hudng ling la su phdn bd Iai didn tfch trong thanh kim loai

2-TKBGV.L11(NC)

17

Boat dong 4

On tap kid'n thurc ve chd't din dien

va chat each didn

Suy nghi cd nhan tim cau tra Idi

- Cha't din didn la cha't cho ddng

didn chay qua

- Chdt each dien Id chit khdng cho

ddng didn chay qua

Ca nhdn tid'p thu, ghi nhd

HS thuc hidn nhiem vu

- Vf du vd chit din dien : Kim loai

cd nhidu dlectron tu do, dung dich

mudi, axit, bazo cd nhidu ion tu do,

- Vi du vd chit each dien : Thuy

tinh, nudc nguydn chit, khdng khf

khd

Suy nghT ca nhdn tim cdu tra Idi

HS bi dua vao tinh thd' bd' tic

- The' nao la chit din didn ? Ch^t each didn?

GV thd chd' hod kid'n thiic :

Dd chit din didn cho ddng didn chay qua dugc thi nd phai cd nhidu hat mang didn cd tfnh chit la cd thd di chuydn duge trong nhihig khoang Idn hon nhidu lln kich thUdc phdn thii ciia vat Nhiing hat dd ggi Id cac didn tich tu do vay nhung vat (chit) cd chfla nhidu didn tfch tu do la nhflng vat (chit) ddn didn Ngugc lai nhflng vdt (chit) cd chiia ft didn tfch tu do la nhflng vdt (chit) each dien

GV ydu clu HS lly cac vf du vd chd't din didn va chit each didn

- Dua vdo tfnh din didn cua mdi trudng, ngudi ta phdn bidt cdc vat din didn va cac vdt cha dien Ndi ring su phdn bidt dd chi cd tfnh tucfng ddi Id ddng bay sai ?

Ca nhdn quan sdt

Thao ludn chung toan Idp

- Vi ddy tdc da bi cdt dut, thuy tinh

khdng din didn ndn bdng den

khdng sdng

HS hi dua vao tinh thd' b^ tie hoac

tinh the'phdn xet

HS quan sdt, tra Idi:

- Dung nhu giai thfch d trdn : d

nhidt do Uiudng ihuy tinh khdng

din dien

- 6 nhiet dd cao thuy tinh din didn

GV gidi thidu bd thi nghidm ehiing minh va neu cdu hdi vd vln dd cin nghidn ciiu

Diing hai bdng den loai 220V -75W, mdt bdng ddp vd

vd cit ddi ddy tdc, hai bdng mdc ndi tid'p vdi nhau (hinh

ve bdn)

- Hien tugng gi xay ra ndu mdc hai diu mach dien trdn vao ngudn didn 220V?

- Hidn tugng gi xay ra nd'u dimg den cdn ddt ndng phin thuy tinh gifla bai chan ndi hai diu day tdc ciia bdng den?

GV ti6h hanh thf nghidm vd ydu clu

HS quan sat dd nit ra ke't luan

- Ldm thi nghidm khi chua ddt den cdn

- Lam thf nghidm khi da ddt den cdn

Thi chd' hoa kid'n thdc : Vay sir phdn

chia cdc chit thanh chit din didn va ch^t each didn chi cd tfnh tuong ddi

19

Boat dong ^

Nghien cdu dinh luat bao toan

dien tich

HS thao luan chung toan ldp

- Tdng dai sd cae dien tfch cua qua

clu kim loai va thanh kim loai trudc

va sau khi tie'p xiic khdng thay doi

Ca nhdn tid'p thu, ghi nhd

Boat dong 6

Cung cd bai hgc va dinh hudng

nhiem vu hgc tap tie'p theo

Ca nhan nhdn nhiem vu hgc tap

- Cd nhan xet gi vd tdng dai sd cdc didn tfch ciia qua clu kim loai va thanh kim loai trudc va sau khi tid'p xiic d thi nghidm nhidm didn do tid'p xuc ?

GV ndu cdu hdi ggi y :

- Dien tfch cua thanh kim loai trudc va sau khi tiep xuc cd thay d6i khdng ? Ndu cd thi thay ddi nhu thd nao ? Tai sao ?

Thdng bao : Ta coi hd gdm qua clu va thanh kim loai d tren khdng trao ddi didn tich vdi cac hd khac, hd nhu vdy ggi la he cd ldp vd didn

GV thdng bao dinh ludt bao toan didn tich

- Cho ddn nay dinh ludt bao toan didn tfch da dugc kidm nghidm trong nhidu kidn khac nhau, nhung ngudi ta chua gap mdt trudng hgp nao chiing td dinh luat nay khdng dugc thoa man

Ydu clu HS hoan thanh bai 1, 2 SGK

GV ydu clu HS Idm vide d nha :

- Lam bdi tap trong phid'u hgc tap sd 2

- On lai khai nidm tfl trudng, tfl phd, dudng siic tfl d ldp 9 THCS

- On lai khai nidm vd trudng hSip din d ldp 10 THPT

- On Iai luc tuong tac Cu-idng

PHl£u HOC T A P S O 1 C5u 1 Hidn tugng gi xay ra ndu cho thanh thuy tinh cg xat vao midhg lua? Giai

thfch tai sao lai cd hien tugng tren ?

Cdu 2 Hidn tugng xay ra ndii ta cho thanh kim loai nhidm didn am tidp xuc vdi qua clu trung hod vd didn va cho thanh kim loai nhidm dien ducfng tidp xiic vdi qua clu trung hoa vd didn? Giai thfch tai sao lai cd hidn tugng trdn ? Cdu 3 Hidn tugng gi xay ra ndu cho thanh kim loai trung boa vd didn lai gin qua

clu nhidm didn am vd cho thanh kim loai trung hoa vd didn Iai gin qua clu nhidm didn duong ? Gidi thich tai sao lai cd hidn tugng trdn ?

PHIEU HOC TAP SO 2 Cdu 1, Chgn cdu sai trong cdc cdu sau

A Trudc va sau khi mdt vat nhidm didn, tdng dai sd cac didn tfch trdn vdt dd luc sau ludn khae vdi luc diu

B Trong mdt hd cd lap vd didn, tdng dai sd eac dien tieh ludn la mdt hang sd

C Trong su nhidm dien do cg sat, su xult bidn cua didn tich dm trdn vat

nay ludn kem theo su y.^jiit hidn cua didn U'ch duong va cd ciing dd ldn trdn

A khdng mang dien tfch

B mang didn tfch am

C mang didn tfch ducfng

D mang didn duong hoac am

CAu 3 Hai qua clu nhu nhau dugc tfch didn cd dd Idn khdc nhau Sau khi dugc cho cham vdo nhau rdi tach ra thi chiing se ludn

A dly nhau B hdt nhau

C trung hod vd didn D khdng dly va cung khdng hdt nhau

21

- Hidu va van dung dugc bidu thdc xac dinh vecto cudng dd didn tturdng vd cudng

do dien trudng ciia mdt didn tfch diem

- Tfl khai niem dudng sflc tfl d ldp 9 THCS bgc sinh dua ra dugc khdi nidm dudng sdc dien Hieu dugc y nghTa ciia dudng sflc didn, quy tie ve cac dudng sflc didn Bidt dugc su gidng va khac nhau gifla cdc " dudng hat bdt" cua didn phd vd cdc dudng sflc didn

- Tra Idi dugc cdu hdi didn trudng ddu la gi va bie't dugc didn trudng bdn trong hai tdrn kim loai tfch didn trai ddu va cd dd ldn bdng nhau Id didn trudng ddu

2 Vi ki nSng

- Quan sdt thf nghidm bidu didn cua GV va rut ra kd't ludn vd hidn tugng vdt If quan sdt dugc

- Tfl hinh anh didn phd ve dugc hinh dang cac dudng sflc didn

- Bidu didn cdc vecto cudng dd didn trudng gdy ra bdi mdt bode nhidu didn tfch didm

- Thie't k^ phuong an thf nghiem didn phd

- Giai mdt sd bdi todn xac dinh cudng dd dien trudng gdy ra bdi mdt hodc vdi dien tfch didm

II-CHUXNBI

Gido vien

Hpc sinh

- On lai khai nidm tfl hudng, tfl phd, dudng sflc tfl d Idp 9 THCS

- 6n Iai khai nidm vd uudng hip din d Idp 10 THPT

- 6n lai luc tuong tac Cu-I6ng

Ill - THifiT Kf HOAT D 6 N G DAY HOC

Boat ddng cua hgc sinh Trg giiip cua giao vi#n

Boat ddng 1

Kidm tra, chuin bi dieu kien

xu^t phat Dat van de

Ca nhdn suy nghT tim cdu tra Idi:

- Tfl trudng tdn tai xung quanh

nam chdm va xung quanh ddng

cin nghien cflu

GV neu cdu hdi kidm tra kid'n thflc cfl :

- Tfl trudng tdn tai d dau ? Lam th^ nao

dd nhan bi^t dugc tfl trudng ? Bidu didn tfl trudng bang hinh ve nhu thd nao ?

DVD : Ta da bid't xung quanh nam cham hoac ddng dien tdn tai tfl trudng, ne'u ta dat mdt nam cham hay ddng didn trong tfl trudng thi nam chdm hay ddng didn se chiu mdt luc tfl tac dung Hai dien tich dat Uong chan khdng khdng tid'p xuc vdi nhau nhung vln hdt hodc dly nhau Chung tac dung len nhau bdng each nao ? Dd tra Idi dugc cau hdi nay chung ta hgc bai: Didn trudng

23

Boat dong 2

Xdy dung khai niem dien

trudng

Thao luan chung todn Idp

- Xung quanh didn tfch tdn tai mdt

trudng vat chit tuong t\x nhu tfl

trudng

— Tinh chat cua trudng dd la tac

dung mdt luc didn ldn didn tich dat

trong nd

Ca nhan tid'p thu, ghi nhd

GV ydu clu HS suy nghT tta Idi cau hdi DVD

- Hai dien tfch dat ttong chan khdng khdng ti^p xuc vdi nhau nhung vln but hoac dly nhau Chung tac dung ldn nhau bang each nao ?

GV ndu cdu hdi ggi y :

- Xung quanh nam cham hoac ddng dien tdn tai tfl trudng va nd tac dung mdt luc tfl ldn nam cham hoac ddng didn khdc dat trong nd Lieu ring xung quanh mdt didn tfch ed tdn tai mdt trudng vat chit cd tfnh chdt tuong tu khdng ?

- N^u tdn tai thi tfnh chit ciia trudng vat chaa dd la gi ?

GV thd chd' hod tti thflc :

- Xung quanh mdt dien tfch diing yen tdn tai mdt didn trudng Tfnh cha't co ban cua dien trudng la nd tac dung mdt luc dien len didn tfch dat ttong nd Chu y : Didn ttudng cua cac dien tfch ddng ydn dugc ggi chfnh xae la didn trudng tTnh Tuy nhidn, trong ttudng hgp khdng sg gay ra nhim lln ta thudng ndi van tat la dien trudng

HS bi dua vao tinh th^ bd tic

Thao luan chung toan ldp

- Vln dung mdt didn tfch thfl q d

trdn thay ddi cdc didn trudng khdc

nhau do luc F tdc dung Idn didn

tfch thfl q

GV ndu muc dich thf nghidm va md ta thf nghidm

- Di nghidn ciiu didn trudng tai mdt

didm xac dinh ngudi ta dung cac didn tfch thfl qi, q2, q3, dat tai didm cin nghidn ciiu, sau dd xdc dinh luc didn tac dung ldn cac didn tfch thfl Fi, Fj, Fj, mong ung

Ngudi ta tha'y rang cdc thuang sd

p; ¥, F3 F , , ^,

'-^ = -^ ^ = = — bang hang sd

qi ^2 q3 q

F Dat E = - -

q

khdng?

GV ndu cau hdi thie't kd phuang an thf nghidm dd tim cau tra Idi cho cdu hdi trdn

- Hay thid't ke' mdt phuang dn thf nghiem de kidm tra xem thuong sd -

- Dac trung cho didn trudng vd

phuang didn tac dung luc

Ca nhdn tid^p thu, ghi nhd

Thao ludn nhdm, sau dd dai didn

nhdm ldn bao cao kd't qua

- Ta cd F = q.E => F cung chidu

vdi E khi q > 0, F ngugc chidu

q

- Thuong sd ndy dac trung cho tfnh chSt

gi cua didn trudng ?

q trudng Kl hidu Id E

- Dd Idn cua vecta E ggi Id cudng dd didn trudng, ki hidu la E, don vi ttong

HS nhd Iai phuang an thi nghidm

da tien hdnh d Idp 9 THCS va phat

bidu trude ldp

- Rdc ddu mdt ldp mat sdt Idn t&n

nhua ttong, phang Dat t ^ nhua

ndy len mdt qua clu da dugc

nhidm dien Quan sat hinh anh mat

sat vfla dugc tao thanh tren t ^

nhua

Suy nghT ca nhdn tim cdu tta Idi

- Diing mdt vdt nhidm didn khdc

cho tidp xuc vao qud clu

GV ndu cdu hdi vd vaii dd cin nghidn cflu

- Ta da bi^t xung quanh didn tich dflng ydn cd didn trUdng Bing mdt thudng chung ta khdng thd nhin thiy dien trudng Vdy cd cdch ndo dd cd thd hinh dung ra didn trudng mdt each dd dang

va thudn Igi ?

GV ndu cdu hdi thid't k^ phuang an thf nghidm dd quan sat hinh anh cua didn trudng

- Hay thie't kd' mdt phuang dn thf nghiem dd quan sdt dugc hinh anh cua didn trudng

GV ndu cdu hdi ggi f di HS thieft kd'

27

Ca nhdn chu y ling nghe va quan

sat thi nghiem

Ca nhdn tid'p thu, ghi nhd

HS nhdn nhiem vu va lam.vide

theo nhdm, sau dd dai didn nhdm

ldn bao cao kdt qua

- Trong thf nghidm nay ngudi ta dung bdt each didn thay cho mat sdt, rdc bdt each didn ndy vao diu each didn Dung may Wim-sdt dd nhidm didn cho qua clu bang kim loai

GV tid^n hdnh thf nghidm, ydu clu HS quan sdt vd rut ra kd't ludn

- Tie'n hanh nhidm dien cho qua clu kim loai bdng may Wim-sdt, go nhe vao khay diu ta thu duge hinh anh slp xdp cua cac hat bdt

GV thdng bao : Hinh anh cac dudng hat bdt thu dugc d thi nghidm ttdn ggi la dien phd ciia qua clu nhidm didn

- Cac dudng iiat bdt cua didn ph6 cho ta hinh anh cac dudng sflc didn

- Hudng cua cac dudng sflc didn trung vdd hudng cua vecta cudng dd didn trudng

GV ndu cdu hdi vd v ^ de cin nghien cflu tid'p

- Ndi eac dudng hat bdt d thf nghidm d ttdn ta cd dudng sflc didn cua didn trudng cua qua clu nhidm didn Tfl hinh anh didn phd; ciia qua clu nhidm didn, didn phd cfla hai qua clu nhidm didn ttdi diu, dien ph6 cua hai qua clu nhidm didn cung dSfu, dien phd cua hai tim kim loai song song nhidm didn ttdi diu (hinh anh cd ttong SGK) hay ve cdc dudng sflc didn eua dien trudng cua cac vdt mang didn d tten va ndu each xac dinh hudng cua cae dudng sflc didn dd?

- Di xac dinh hudng ciia dudng

sflc didn ta dat mdt dien tfch thfl

ttdn dudng sflc dien, xac dinh

hudng cua luc didn tac dung len

dien tfch thfl, tfl dd suy ra hudng

cua vecta eudng dd didn trudng va

hudng cua dudng sflc dien

Ca nhdn tidp thu, ghi nhd

Boat dong 5

Xdy dung khai niem tfl trudng

ddu

Thao ludn chung toan ldp

- Cae dudng sflc ttong Idng gifta

hai tain kim loai nhidm dien ttdi

diu song song va each ddu nhau

ndn cdc vecto cudng dd dien

trudng bdng nhau

GV ndu cdu hdi ggi y :

- Cd thd xac dinh hudng cua dudng sflc didn thdng qua hudng cua vecto cudng

dd dien ttudng dugc khdng ?

- Mudn xdc dinh hudng cua vecta cudng dd dien trudng ta phai lam thd' ndo ?

- Cd thd dung mdt didn tfch thfl dat ttong didn ttudng va xac dinh hudng cua luc didn tac dung ldn didn tfch thfl tfl dd xac dinh hudng cua vecta cudng dd dien trudng duge khdng ?

GV thd che hoa tti thflc

- Vdy dudng sflc dien la dudng cd hudng dugc ve ttong didn trudng sao cho hudng cua tiep tuydn tai didm bat ki didm nao ttdn dudng cung trung vdi hudng cua vecta cudng dd didn trudng tai didm dd

GV thdng bdo cac tfnh chit cua dudng sflc didn

GV ndu cau hdi vd VEQI de cin nghien cflu

- Cac vecta cudng dd didn trudng tai cac didm trong Idng cua hai tdm kim loai song song nhidm dien trai diu cd dac didm gi ?

GV ndu cau hdi ggi ^ :

- Tfl hinh anh cdc dudng sflc didn ttong long cua hai tdm kim loai, hay nhdn xet

29

Boat ddng 6

Tim hidu dien trudng ciia mot

dien tich diem va nguyen If

chdng chd't dien trudng

Thao ludn nhdm, sau dd dai didn

nhdm ldn bao cao ket qua

- Dat didn tfch thfl q tai vi trf r, dd

Idn cua luc didn tdc dung vao didn

- M6t didn trudng ma vecta cudng dd didn trudng tai mgi didm ddu bdng nhau ggi la dien trudng ddu

GV ndu cdu hdi vd vSfli dd cin nghidn ciiu

- Xac dinh cudng dd didn trudng tai mdt diem gdy ra bdi mdt didn tich didm

Q dat ttong didn mdi vd han va cdch didn tich didm Q mdt khoang r ?

GV ndu cdu hdi ggi y :

- Di xac dinh cudng dd didn trudng ta

phai sfl dung cdng thflc nao ?

F

- Ap dung cdng thflc E = —, ta cin phai

q tfnh dugc nhiing dai lugng nao ?

- Didn tfch q phai ddt tai vi tri nao ?

- Hudng cua vecta cudng dd didn trudng phu thudc nhu the ndo vao Q ?

Cd nhdn tidp thu, ghi nhd

Boat dong 7

Cung cd bai hgc va djnh hudng

nhidm vu hoc t&p tid'p theo

HS hoat ddng cd nhdn, sau dd ttao

ddi nhdm vd dai didn nhdm ldn

bao cao kdt qua

Ca nhdn nhdn nhidm vu hgc tdp

' GV thdng bao : Gia sfl ta cd hd hai didn tich didm Q„

Qj Didn trudng cua dien tfch Q, la E,, didn trudng cua didn tfch Qj la £3 - Didn trudng cua hd d mdt didm la E thi ta cd bidu thflc: E = E, + E2

Bidu thflc trdn id bidu thflc cua nguydn li chdng chit didn trudng hay nguyen Ii cdng didn trudng

GV ydu clu HS lam vide vdi phieu hgc tdp sdi

Hoan thanh d Idp cac bai 1, 2 SGK Hudng din hgc bai d nhd :

- Lam bai tdp d phid'u hoc tdp sd 2

Cku 2 Chflng mmh rang tai mdi didm ttong didn trudng ta chi ve dugc mdt va chi

mdt dudng sflc didn chay qua ?

31

Cau 3 Cd trudng hgp nao dudng sflc khdng xuSit phat tfl cac didn tfch duong va

tan cung d didn tfch dm khdng ? Lay vi du ?

PHIEU HOC TAP S 6 2

Cau 1 Mdt hat bui khdi lugng 3.10"^kg dugc tfch dien tfch 3|iC Dd hat bui

la Iiing ttong khdng khf (lly g = lOm/s^) thi cudng dd dien trudng cd dd ldn la

A 6 V/m

B 8V/m

C 10 V/m

D 12 V/m

Cau 2 Dudng sflc cua didn trudng cho biet

A Hudng cua luc didn tac dung vao didn tfch dat trong didn trudng

B Hudng cua vecta cudng dd didn trudng tai mdi didm ma nd di qua

C Dd ldn cua didn trudng

D Dd ldn cua lire dien tac dung vao didn tfch ddt trong didn trudng

Cau 3 Trong cac vec ta dien trudng sau, vec ta nao bidu didn sai:

A Vec ta E^

B Vec ta Eg

C Vec to Ec

D Vec to En

CAu 4 Chgn cdu tra Idi dung

Chung ta coi rang dien tnrdng la deu nhu hinh ve Cd bao nhidu didm trdng cd cung didn th^ nhu didm den:

- Hidu dugc khai nidm bidu didn thd

- Hidu dugc mdi lien he gifta cdng cua luc didn trudng va hidu didn thd' Bid't each vdn dung cdng thflc vd mdi hen hd giibi hai dai lugng dd

- Hidu dugc mdi lidn hd gifta cudng dd didn trudng va hidu dien the' va bi^t each vdn dung cdng thflc hdn he gifla hai dai lugng dd

2 Vi ki n&ng

- Bid'n d6i toan hgc dd xdy dung cdc bidu thflc tinh cdng cua luc didn, bidu thflc hidu didn thd', bidu thflc mdi lien he gifta cudng dd didn trudng va hidu didn th^

- On lai khai nidm ve cdng d ldp 10 THPT

- On lai luc tuong tac Cu - Idng, eudng dd didn trudng

Ill - THlfiT K£'HOAT D O N G DAY HOC

Boat ddng cua hoc sinh

Boat dong 1

Kiem tra, chu^n hi dieu kien

xuait phat B\D

Cd nhdn suy nghT tim can tta loi

Ca nhan nhan thflc dugc vln dd

cin nghidn cflu

Boat dong 2

Xay dung bieu thiirc tinh cong

cua luc dien

HS thuc hidn nhidm vu

Trg giiip cua giao vidn

GV dat cau hdi cung nhic lai kid'n thflc

da hgc

- Viet bidu thflc cdng ca hgc ? Cho bi^t cdng ca hgc phu thudc vdo nhflng yd'u td nao ? Cdng cua trgng luc phu thudc vdo yd'u td nao, vd dugc bidu didn nhu thd nao?

DVD : Bai trudc chung ta da nghidn cihi

ve luc didn, hdm nay chung ta nghidn cflu xem cdng cua luc didn phu thudc vdo nhflng y^u td nao vd nd dugc bidu didn qua dai lugng nao ?

GV neu cdu hdi vd vdii dd cin nghien cflu

- Cdng cua luc didn trudng phu thuOc vao nhihig yeu td nao ?

M' R' P' Q- S' N'

- Coi doan dudng cong MN dugc

chia thanh nhidu doan nhd sao cho

mdi doan thang nhd dd cd thd coi

Id mdt doan thing Khi dd cdng

ciia lue didn ttdn mdt doan nhd dd

dugc xac dinh nhu sau :

AApQ = qE.PQcosa = qE.Fo"

; GV phat phie'u hgc tdp cho HS , yeu clu

; HS lam vide ca nhdn, sau dd ttao ddi

; nhdm va dai didn nhdm Idn bao cao ket

- Gia sfl dien tich q > 0, lire didn ttudng

cd chidu nhu th^ ndo ?

- Vi quy dao chuydn ddng cua didn tfch

q la mdt dudng cong nen mudn tinh dugc cdng cua luc didn trudng lam dien tfch q chuyen ddng tren dudng cong dd

ta phai lam the" ndo?

vdi PQ' la hinh chi^u cua PQ len :

true Ox; true Ox cd chidu trung :

vdi chidu cua dudng sflc j

Suy ra cdng trdn toan doan MN i

bdng: i

A K, = 2 ] A A I *-MN

= qE(M'R'+ + P'Q*+ + S'N') j

= qEM'N' i

M',N'la hinh chidu cua hai didm j

M, Nidn true Ox i - Ndu q < 0 thi bieu thflc cdng cua luc

i didn dugc vie't nhu the' nao ?

35

Nd'u q < 0 thi bidu thflc cdng cua

luc dien vln dugc viet nhu tren

AMN=qEM'N*

- Cdng cua Iuc didn tac dung ldn

mdt didn tfch khdng phu thudc

dang dudng di cua dien tfch ma chi

phu thudc vao vi trf didm diu va

didm cudi cua doan dudng di ttong

HS suy nghi cd nhdn tim cdu tta Idi

- Bidu didn cdng cua luc didn khi

didn tich q di ehuydn tfl didm M

dien didm N qua hidu cua cdc th^

nang cua didn tfch q tai hai didm

- Tfl bidu thflc tfnh cdng cua lue dien, hay rflt ra nhdn xet vd su phu thudc cua cdng cua Iuc dien vao dang dudng di ?

- Hay neu su gidng nhau gifta didn trudng tinh va trudng hip din ?

GV thd che' boa tri thflc

- Nhic lai bieu thflc tinh cdng cua luc didn vd dac didm dinh tinh cua cdng cua luc didn

GV ndu cdu hdi vd vln dd cin nghidn cflu tidp

- Cong cua Iuc didn cd thd dugc bidu didn qua dai Iugng nao ?

GV neu cdu bdi ggi y :

- 0 ttdn ta da rut ra dac didm chung gifta cong cua Iuc didn va cdng cua ttgng Iuc, mat khac ta da bidt cdng cua Iuc ttgng Iuc cd thd dugc bidu didn qua hidu the' nang tai vi ttf diu vd cudi dudng di cua vdt, lidu cd the bidu didn cdng cua Iuc didn tuang tu nhu cdng cua ttgng luc dugc khdng ? Ndu dugc thi , bidu thflc duge viet the' nao ?

Ca nhdn tta Idi cdu hdi:

V - V =^^

Cd nhdn tta Idi

- Vdn la hidu didn thd gifla hai

didm M, N md khi cd mdt didn tfch

duang IC di chuydn tfl didm M

ddn didm N thi luc didn trudng se

thuc hien mdt cdng duong la U

GV thdng bao Hidu the nang cua vat ttong ttgng trudng ti Id vdi khdi lugng m cua vat Tuang tu, cung cd thd coi hieu thd' nang cua didn tfch q ti Id vdi didn tich q ngbia la cd thd bidu didn A^^dudi

d a n g : A^j, = q ( V „ - V j , )

Trong dd {V^-V^)d\xac ggi la hidu

dien the gifla hai didm M, N ( cdn ggi

Id didn dp gifla hai didm M, N)

yeu clu HS rut ra cdng thflc tfnh hidu didn the' gifla hai didm M, N

Thdng bao : Cdng thflc nay cho phep

ta xac dinh hieu didn th^ nhung khdng xac dinh mdc tinh didn thd' Didn th^ cua dien tfch phu thudc vao each chgn mdc tfnh didn the Thdng thudng ngudi ta chgn didn th^ d mat da't Idm mdc ( nghia la dien thd d mat ddt bang khdng), cung cd khi chgn didn thd d xa vd cue bang khdng

Dd cho ggn ngudi ta dat nhu sau :

V - V = u '-'MN ~ '-'NM Dan vi cua hidu didn thd la vdn, ki

hidu V vay ndu V^= IV q = IC

t h i A ^ = l J Ydu clu HS dinh nghia IV

37

Hoat ddng 4

Xdy dung bidu thflc lidn hd gifta i

didn trudng v^ hieu dien the

HS thuc hidn nhidm vu i

Ta cd: j

TT _ A M N _ q E M ' N ' i

q q

M'N' i

Ca nhan ti^p thu kien thflc

GV gidi thidu dung cu do hidu didn the' va each sfl dung cu dd

Dung cu dung dd do bidu didn the' Id tinh didn k^

- Didn trudng va hidu didn th^ cd lidn

he vdi nhau nhu th^ ndo ? Xdy dung bidu thflc bidu didn mdi lien hd dd ?

GV ydu clu HS Idm tidp tuc Idm vide vdi phie'u hgc tdp

GV neu cdu hdi ggi y :

- Tfl bidu thflc cua hidu didn th^ hay bidu didn cdng cua Iuc didn theo cudng

dd didn trudng ?

GV thd che boa tti thflc : Trong trudng hgp khdng cin dd y ddn diu cua cac dai Iugng thi ta cd thd vid't:

d Vdi d la khoang each gifta hai didm M' N'