tom tat cong thuc vat ly 11.14537
TRANSCRIPT
01689.996.187
forum: lophocthem.name.vn - [email protected]
lch hc: 5h th3+5
CC CNG THC TNH NHANH TRONG BI TP TRC NGHIM.
- Cc n v o lng c bn.-
K hiu, tn gi, n v i lng vt l. Cng thc b tr ton l.
Su tp, bin son: V NH HONG http://lophocthem.name.vn - [email protected] T: 01689.996.187 - 01272.328.017
Thi nguyn 2011-2012
ng tuy gn khng i, khng n, vic tuy nh khng lm chng xong!
1
01689.996.187
forum: lophocthem.name.vn - [email protected]
lch hc: 5h th3+5
Chng I: in tch - in trng.1. Vt nhim in_ vt mang in, in tch_ l vt c kh nng ht c cc vt nh. C 3 hin tng nhim in l nhim in do c xt, nhim in do do tip xc v nhim in do hng ng. 2. Mt vt tch in c kch thc rt nh so vi khong cch ti im ta xt c gi l in tch im. 3. Cc in tch cng du th y nhau, tri (ngc) du th ht nhau. 4. nh lut Cu_Lng (Coulomb): Lc ht hay y gia hai in tch im t trong chn khng c phng trng vi ng thng ni hai in tch im , c ln t l thun vi tch ln ca hai in tch v t l nghch vi bnh phng khong cch gia chng Cng thc:F =k q1 .q 2 r22 1 = 9.10 9 ( N .m ) Vi k = 4 . 0 C2
q1, q2 : hai in tch im (C ) r : Khong cch gia hai in tch (m) 5.Lc tng tc ca cc in tch trong in mi (mi trng ng tnh) in mi l mi trng cch in. Cc th nghim chng t rng, lc tng tc gia cc in tch im t trong mt in mi ng cht, chim y khng gian xung quanh in tch, gim i ln khi chng c t trong chn khng: : hng s in mi ca mi trng. (chn khng th = 1) .r 2 6. Thuyt electron (e) da vo s c tr v di chuyn ca cc e gii thch cc hin tng in v cc tnh cht in ca cc vt. Trong vic vn dng thuyt e gii thch cc hin tng nhim in (do c xt, tip xc, hng ng), ta tha nhn ch c e c th di chuyn t vt ny sang vt kia hoc t im ny n im kia trn vt. 7.cht dn in l cht c nhiu in tch t do,cht cch in(in mi) 8. nh lut bo ton in tch: Trong mt h vt c lp v in, tng i s ca cc in tch l khng i.F =k q1 .q 2
- Quy tc tng hp lc: Quy tc hnh bnh hnh r r r r r Nu vt chu tc dng ca 2 lc F1 , F2 th F = F1 + F2 + F1 F2 F = F1 + F2 + ( F1 , F2 ) = 900 F = F12 + F22r r r r r r r
+ F1 F2 F = F1 F2 + ( F1 , F2 ) = F = F12 + F22 + 2 F1 F2 cos
r
Nhn xt: F1 F2 F F1 + F2 IU KIN CN BNG CA MT IN TCH. PP Chung Khi kho st iu kin cn bng ca mt in tch ta thng gp hai trng hp: . Trng hp ch c lc in: - Xc nh phng, chiu, ln ca tt c cc lc in F1 , xt. - Dng iu kin cn bng: F1 + F2 + ... = 0 - V hnh v tm kt qu.
F2 , tc dng ln in tch
ng tuy gn khng i, khng n, vic tuy nh khng lm chng xong!
2
01689.996.187
forum: lophocthem.name.vn - [email protected]
lch hc: 5h th3+5
. Trng hp c thm lc c hc (trng lc, lc cng dy, ) - Xc nh y phng, chiu, ln ca tt c cc lc tc dng ln vt mang in m ta xt. - Tm hp lc ca cc lc c hc v hp lc ca cc lc in. - Dng iu kin cn bng: R + F = 0 R = F (hay ln R = F).
2. in trng. - in trng tnh l do cc ht mang in ng yn sinh ra. - Tnh cht c bn ca in trng l n tc dng lc in ln in tch t trong n. - Theo quy c v chiu ca vect cng in trng: Vct cng in trng ti mt im lun cng phng, cng chiu vi vect lc in tc dng ln mt in tch dng t ti im trong in trng. PP Chung . Cng in trng ca mt in tch im Q: p dng cng thc E =Q F =k . q1----------------q .r 2
E1
q1------------------q1
E1
(Cng in trng E1 do q1 gy ra ti v tr cch q1 mt khong r1 : E1 = k 1)
.r1 2
,
Lu cng in trng E l mt i lng vect. Trong chn khng, khng kh = n v chun: k = 9.109 (N.m2/c2 ), Q (C), r (m), E (V/m) 3. Cng ca lc in v hiu in th.
1. Khi mt in tch dng q dch chuyn trong in trng u c cng E (t M n N) th cng m lc in tc dng ln q c biu thc: A = q.E.d Vi: d l khong cch t im u im cui (theo phng ca E ). V th d c th dng (d> 0) v cng c th m (d< 0) C th nh hnh v: khi in tch q di chuyn t M N th d = MH. V cng chiu vi E nn trong trng hp trn d>0. E F Nu A > 0 th lc in sinh cng dng, A< 0 th lc in sinh cng m. 2. Cng A ch ph thuc vo v tr im u v im cui ca ng i trong in trng m khng ph thuc vo hnh dng ng i. Tnh cht ny cng ng cho in trng bt k (khng u). Tuy nhin, cng thc tnh cng s khc. in trng l mt trng th. 3. Th nng ca in tch q ti mt im M trong in trng t l vi ln ca in tch q: WM = AM = q.VM. AM l cng ca in trng trong s dch chuyn ca in tch q t im M n v cc. (mc tnh th nng.) 4. in th ti im M trong in trng l i lng c trng cho kh nng ca in trng trong vic to ra th nng ca in tch q t ti M. W A VM = M = M q qng tuy gn khng i, khng n, vic tuy nh khng lm chng xong! 3
01689.996.187
forum: lophocthem.name.vn - [email protected]
lch hc: 5h th3+5
5. Hiu in th UMN gia hai im M v N l i lng c trng cho kh nng sinh cng ca AMN in trng trong s di chuyn ca in tch q t M n N.
U MN = VM VN =
6. n v o in th, hiu in th l Vn (V) Dng 1: TNH CNG CA LC IN. HIU IN TH. PP Chung - Cng ca lc in tc dng ln mt in tch khng ph thuc vo hnh dng ng i ca in tch m ch ph thuc vo v tr ca im u v im cui ca ng i trong in trng. Do , vi mt ng cong kn th im u v im cui trng nhau, nn cng ca lc in trong trng hp ny bng khng. Cng ca lc in: A = qEd = q.U Cng ca lc ngoi A = A. 1 1 nh l ng nng:AMN = q.U MN = m.v 2 N v 2 M Biu thc hiu in th: U MN =2 AMN q 2
q
H thc lin h gia cng in trng hiu in th trong in trng u: E =
U d
4. T in. - Cng thc nh ngha in dung ca t in:C= Q U
- in dung ca t in phng:C= S 9 9.10 .4d
- in dung ca n t in ghp song song: C = C1 + C2 + ......+ Cn - in dung ca n t in ghp ni tip:1 1 1 1 = + + ..... C C1 C2 Cn
- Nng lng ca t in:W= QU CU2 Q2 = = 2 2 2C E 2 w= 9 9.10 .8
- Mt nng lng in trng:
1. T in l mt h gm hai vt dn t gn nhau v cch in vi nhau. T in dng tch in v phng in trong mch in. T in thng dng l t in phng. K hiu ca t in: 2. Ni hai bn ca t in vi hai cc ca ngun in th t in s b tch in. ln in tch hai bn t bao gi cng bng nhau nhng tri du. Ngi ta gi in tch ca t in l in tch ca bn dng.ng tuy gn khng i, khng n, vic tuy nh khng lm chng xong! 4
01689.996.187
forum: lophocthem.name.vn - [email protected]
lch hc: 5h th3+5
3. i lng c trng ca t in l in dung ca t. in dung C ca t in l i lng c trng cho kh nng tch in ca t in mt hiu in th nht nh. N c o bng thng s ca in tch Q ca t vi hiu in th U gia hai bn ca n.C= Q U
n v o in dung ca t in l fara (F)
1 mF = 10-3 F. 1 F = 10-6 F. -9 1 nF = 10 F. 1 pF = 10-12 F. . .S .S - in dung ca t in phng: C = o = d 9.109 .4. .d1 F 1 N.m 2 9 12 8,85.10 ( ) ; k= = 9.10 ( 2 ) Trong : o = m 4. . o C 9.10 9 .4. Q Lu : Trong cng thc C = , ta thng lm tng C l i lng ph thuc vo Q, ph thuc U
vo U. Nhng thc t C KHNG ph thuc vo Q v U. 4*. Ghp t in (xem k): Ghp ni tip: C1 C2 Cn1 1 1 1 = + + ... + Cb C1 C2 Cn
Ghp song song: Cb = C1 + C2 + ... + Cn. Qb = Q1 + Q2 + + Qn. Ub = U1 = U2 = = Un.Q2 1 = Q.U =cu^2/2 2.C 2
Qb = Q1 = Q2 = = Qn. Ub = U1 + U2 +...+ Un.
5. in trng trong t in mang mt nng lng l: W =
- in trng trong t in l in trng u. - Cng thc lin h gia cng in trng E bn trong t in, hiu in th U v khong cch d gia hai bn l:E= U d
- Nu cng in trng trong lp in mi vt qu mt gi tr gii hn Emax th lp in mi tr thnh dn in v t in s b hng. Nh vy, hiu in th gia hai bn t in khng c vt qu gii hn c php: Umax = Emax.d Dng : GHP T IN CHA TCH IN. PP Chung: - Vn dng cc cng thc tm in dung (C), in tch (Q), hiu in th (U) ca t in trong cc cch mc song song, ni tip. - Nu trong bi ton c nhiu t c mc hn hp, ta cn tm ra c cch mc t in ca mch ri mi tnh ton. - Khi t in b nh thng, n tr thnh vt dn. - Sau khi ngt t in khi ngun v vn gi t in c lp th in tch Q ca t vn khng thay i. i vi bi ton ghp t in cn lu hai trng hp: + Nu ban u cc t cha tch in, khi ghp ni tip th cc t in c cng in tch v khi ghp song song cc t in c cng mt hiu in th. + Nu ban u t in (mt hoc mt s t in trong b) c tch in cn p dng nh lut bo ton in tch (Tng i s cc in tch ca hai bn ni vi nhau bng dy dn c bong tuy gn khng i, khng n, vic tuy nh khng lm chng xong! 5
01689.996.187
forum: lophocthem.name.vn - [email protected]
lch hc: 5h th3+5
ton, ngha l tng in tch ca hai bn trc khi ni vi nhau bng tng in tch ca chng sau khi ni). CHUYN NG CA HT MANG IN TRONG IN TRNG Khi ht mang in c th t do khng vn tc u trong mt in trng u th di tc dng ca lc in , ht mang in chuyn ng theo mt ng thng song song vi ng sc in. Nu in tch dng (q >0) th ht mang in (q) s chuyn ng cng chiu in trng. Nu in tch m (q Dthng + Cch khc phc: Mt phi eo 1 thu knh phn k sao cho qua knh nh ca cc vt hin ln im Cv ca mt. nn khi eo knh st mt th : fK = - OCv. - c im ca mt vin : + Khi khng iu tit c tiu in nm sau mng li fmax > OV ; OCC > ; OCv : o sau mt . Dvin < D thng. + Cch khc phc : eo mt thu knh hi t nhn vt gn nh mt thng, nh ca vt to bi knh l nh o nm CC ca mt vin. 4. Knh lp : nh ngha,cng dng,cch ngm chng im cc cn v ngm chng v cc, s bi gic + Tng qut : G = k OC cd' + l
+ Ngm chng cc cn: d ' + l = OC c = Gc = k cng tuy gn khng i, khng n, vic tuy nh khng lm chng xong! 16
01689.996.187
forum: lophocthem.name.vn - [email protected]
lch hc: 5h th3+5
+ Ngm chng v cc : G = OC c f
5. Knh hin vi : Cu to, cng dng, cch ngm chng + Tng qut : G = k OCc = k .G1
d2 ' + l
1
2
+Ngm chng v cc : G = .OC c f1 . f 2
( = F '1 F ' 2 = O1O2 ( f 1 + f 2 )
)
6. Knh thin vn : cu to,cng dng, cch ngm chng- Knh thin vn gm vt knh l thu knh hi t c tiu c ln v th knh l thu knh hi t c tiu c nh. - Ngm chng l quan st v iu chnh khong cch qia vt knh v th knh sao cho nh ca vt nm trong khong thy r ca mt.G = f1 f2
v O1O2 = f1 + f 2 S bi gic khi ngm chng v cc: G = k1.G2 (vi k1 l s phng i ca nh A1B1 qua vt knh, G2 l s bi gic ca th knhG = f1f2
(vi l di quang hc ca knh hin vi)
=l f 1 f 2
f1 : tiu c vt knh ; f2 : tiu c th knh ; l: khong cch gia vt knh v th knh Ph bn MT S KIN THC TOAN C BAN CN CHO VT LYI. Tam thc bc hai. a.x2 + b.x + c =0 iu kin co nghim: = b 2 4ac 0 Du bng xay ra phng trinh co nghim kep x = II.Ham s bc hai. y = a.x2 + b.x + c a>0 Ham y(x) co b lom quay ln. Ta co cc tiu. a