_________________________________________________V~Ir&~TRE

GIO'ITHItu cAe DE THI

DE THI TUYEN SINH LOP 10TRUONGTHPTCHUYENLE HONG PHONG NAM DJNH

Nam hoc 2013-2014

Call 1: (1,5 diem)

Mot v~t hinh l~p phirong co canh dai 2 m, kh6i hrong104kg nam 0 day h6 co d<) sau 10m. Dung tall de true

vot v~t len voi v~n t6c khong d6i (Hinh 1). Trong quatrinh true vat, ke ill khi v~t b~t d~u nho len m~t h6d~n khi v~t vira len hoan toan khoi mat h6, hrc d~yAc-si-rnet luon thay d6i va co the thay bang m<)t lireco d<) Ian khong d6i b~ng mot 111lahrc d~y Ac-si-rnet160 nhfrt tac dungvao vat. Bi~t trongluong rieng cua mnrcd = 104 N / m3

• Boqua lire ma sat giiiaday va rong roc,trong hrong cua day,lire d~y Ac-si-mettac dung len day. _

a. Neu tac dung cua rong roc c6 dinh khi true vot v~t.Tnroc khi v~t nho len m~t h6, tinh d<)Ian lire keo theophirong n~m ngang tai d~u A cua day.

h. Tinh cong cua lire keo nam ngang tai dfru A trangqua trinh true vat v~t cho d~n khi v~t vira len hoanto an khoi m~t h6.

Call 2: (2,0 diem)

Tren m~t ban n~m ngang co mot binh hinh tru, bankinh day R) = 15 cm clnra mroc 0 nhiet d<) I) = 15°C.

Tha mot qua du d~c bang nhom co ban kinhR2 = 5 em 0 nhiet d<) 12 = 45°C vao binh thi khi quadu n~m can bang mire mroc trong binh ngap chinhgitra qua duo B6 qua su trao d6i nhiet voi blnh vamoi tnrong. Cho kh6i hrong rieng cua mroc laD) = 1000 kg / m3

, kh6i hrong rieng cua nhom la

D2 = 2700 kg / m3, nhiet dung rieng cua mroc la

c) = 4200J / kg.K va nhiet dung rieng cua nhorn la

c2 = 880J / kg.K .

a. TIm nhi~t d<) cua mroc khi co can bang nhiet.

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h. D6 them d~u 0 nhiet d<) 13 = 10°C vao blnh cho

vira du ngap qua duo Cho kh6i luong rieng va nhietdung rieng cua d~u la D3 = 800 kg / m3 vac3 = 2800J / kgX.

- Tim nhiet d<) cua h~ khi co can b~ng nhiet,

- Tinh ap sufrt do chfrt long gay ra 0 day blnh va ap hrccua qua du len day blnh.

Call 3: (4,0 diem)

a. Cho mach dien nhir hinh ve (Hlnh 2). Hai dfru doanmach co d~t hieu dienth~ khong d6i U =:= 8 V.Cho RI = 3n, R2 = 3n,R3 = zn, AB la bi~ntro co the thay d6igia tri nho con chayC. Ampe k~, day n6iva khoa K co di~n trokhong dang ke.

- K me, di chuyen con chay C nguoi ta nhan thfry khidien tro phan AC cua bi~n tro AB co gia tri In thicuong d<) dong di~n qua R) nho nhfrt. Tinh di~n trotoan ph~n cua bien tro,

- Dung mot bien tro' khac thay th~ bien tro ban d~u 0mach dien r6i dong khoa K. Khi di~n tro phfrn AC co

gia tri 6 thi ampe k~ chi % A. Tinh dien tro toan

phan cua bien tro maio

h. Mot bang di~n co 8 bong den duoc danh s6 ill Id~n 8; 4 ch6t A, B, C, D va I khoa K nhir hlnh ve(Hinh 3). Cac bong 1,6, 7 ghi 6 V-I W; cac bong 2,5, 8 ghi 3 V - 0,5 W; bong 3 ghi 1,5 V - 0,25 W; bong4 ghi 12 V - 2 W. Hai d~u doan mach MN co d~t hi~udien th~ khong d6i U. Bo qua di~n tro cua day n6i vakhoa K.

Khi K 0 A cac bong 1, 2, 3,4 sang blnh thirong.

Khi K a B cac bong 3, 4, 7, 8 sang binh thirong.

Khi K 0 C cac bong 3, 4, 5, 6 sang blnh thuang.

(Trang khi cacbong sang binhthirong thi cacbong con lai khongsang do khong codong di~n di qua).Hay giai thich vave sa d6 mach di~n ?Tinh hieu di~n th~U?

K

B c A

(8) 2

(8)7 (8)6ABCK'\_--_~p

~ N

17

,,~~&11JCI11IE _

Cau 4: (1,5 diSm)Mot th~u kinh h9i tu tieu cu 15 em co duong ria ladirong trim. Tai tieu diSm v~t F co diSm sang S, taitieu diSm anh F' d~t man E vuong goc voi true chinh.

a. Ve duong di cua churn tia sang xu~t phat ill S toig~p th~u kinh tao vSt sang tren man. VSt sang co hinhdang va kich thuoc nhir thS nao ?

b. Th~u kinh va man duoc d~t c6 dinh. Tir vi tri band~u cho diSm sang S chuyen dong d~u doc theo truechinh, ra xa th~u kinh voi van t6c v = 30 cm/s sancho luon thu diroc vSt sang tren man:

- Kich thiroc vSt sang tren man thay d6i nhu thSnao ? T~i san ?

- Sau bao lau di~n tich vSt sang tren man thay d6i di9 I~n so voi dien tich vSt sang ban d~u ?

Cau 5: (1,0 diem)Cho cac dung cu sau:

- Met chau to dung mroc (kh6i IUQ'ngrieng cua mroclaDn);

- Mdt c6c co dang hinh tru, day va thanh c6c co cungd(> day. BiSt thS tich ben trong cua c6c la Vo, kh6ihrong cua c6c la M. Tren thanh ngoai cua c6c, cokhac cac vach chia dS do thS tich va do do cao cuachat long trong c6c.

Bo qua su dinh trot, hay d~ xuat mot phuong an thircnghiern dS xac dinh ducc:

- Dien tich day ngoai S, do day I cua c6c.

- Kh6i hrong rieng D; cua ch~t lam c6c then cac daiIuong S, 1, M, Yo.

(Yeu C&U: Neu r5 cac biroc tiSn hanh, cac phep doc&nthiet trong thi nghiem).

DA.PA.NCau 1. a)Rong roc lam thay d6i phuong cua luc.

Trong hrong cua v~t la: P = mg = 105 N .

Lire dfty Ac-si-met cue dai tac dung len v~t la:FA =d.v=8.104N.

Lire keo cua day tai diem A tnroc khi v~t nho Ien mat~ 4ho: F, +FA = P~ F, = P-FA = 2.10 N

b)Lvc keo cua day tai d~u A khi v~t b~t d~u nho lenm~t h6 dSn khi vira len hoan toan khoi m~t h6:

1 1F'k+-FA =P~F'k =P--FA =6.104N2 2

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Cong cua hrc keo theo phuong nam ngang tai d~u Acua day khi v~t 6 duoi m~t h6:AI =Fk(h-l)=1,6.105J.Cong cua lire keo then phuong n&m ngang tai dfruAcua day khi v~t b~t d~u nho len m~t h6 dSn khi viralen hoan toan khoi mat h6:A2 = F 'k I = 1,2.105 J.

Cong cua lire keo n&mngang tai d~u A trong su6t quatrinh true vot v~t cho dSn khi vat len khoi mat h6: Al+ A2 = 2,8.105 J.

Cau 2. Kh6i hrong cua mroc trong binh la:

( 2 1 4 3)ml =VPI = 1lR,.R2-2·31l~ D,r:::;3,27kg

Kh6i Iuong cua qua C&Ula:4 3

m2 = V2D2 = -1lR2D2 r:::; 1,41kg3

Phuongtrinh can bang nhiet: clml (I - II)= c2m2 (/2 - I)_ - c.m.t, +c2mi2 -17 5De-> t - - ,

clml +c2m2

b) ThS tich cua d~u va mroc bang nhau nen kh()i, mc-D;

hrong cua dau la: m3 = D :::::2,62 kgI

Tuong tv nhir tren, nhiet do cua h~ khi co can bangnhiet la:

t = clml!1 +c2m2t2 +C3m3t3 :::::15 o-cx ,

clml + c2m2 + c3m3

Ap su~t do ch~t long gay ra 6 day binh la:p = 10(DIR2 +D)R2) =900Pa

Ap hrc cua qua C&Ulen day binh la:

1 4 3 ( )F=l(call)-FA(Cau)=10m2--.-1[R2 DI+D3 ·102 3

:::::9,39N

Cau 3. a) * K mer:GQi R la di~n trotoan phan, x 1a dientro phan AC, R-x ladien tro ph~n BC.

Ve lai mach dien Bnhir hinh ben.

. Dien tro toan mach la:

R -R- 3(x+3) R _ -x2+(R-I)x+21+6R1m - x+ + 3 ---...:..--"-----

x+6 x+6

+U

SO 122 THANG 10 - 2013

. - .. ,------------------------ V~Dr&~TREcan 4. Khi v~t d~t tai tieu di€m F: chum tia 16songsong voi true chinh nen v~t sang tren man co danghinh tron va co kich thuoc cua b€ m~t thftu kinh,

b) Thau kinh va man c6 dinh, dich chuyen S tren truechinh va ra xa thftu kinh, d > f nen S 1 ' la anh th~t.

M~ •.......••=--=-----;-=---- -- ~SI S/", 0

~~---.t~--~-----=~------

~ I=~= 8(x+6)Rim _X2 +(R-1)x+21+6R

Cirong dl) dong di~n qua RI la:24

1=--------I -x2+(R-l)x+21+6R

Cuong dl) dong di~n qua R, nho nhftt => II nho nhfttR-l

=>x=-2-=1 =>R= 3 (n)

* Khi K dong

- Ve lai mach di~nnhu hinh ve.

R' la dien tro toanph~n, dien trophan, RAC = 60, A,

dien tro ph~n BCla R'- 60

R3.------._+ U ••..----..._..r-,

R,

f)'A " h 17R'-60ien tro toan mac : R/ = ----• • m 4(R'-3)

, dA d' d'A h hi h I 32(R'-3)Cuang 0 ong ien mac c In: = --'-----'-. .. 17R'-60

Cirong dl) dong di~n qua dien tro (R' - 6):

I _ 48(R'-6) - 17R '_ 60 I A = 1- I(R'_6) •

=> 32(R'-3) 48 =~ => R' = 12 (n)17R'-60 17R'-60 3

b) Tinh dung dong di~n dinh rmrc qua cac den bang ~ A

Ghii thich:

K == A ~ DI; D2; D3; D4 m~c n6i ti~p voi nhau

K == B ~ D3; D4; D7; Dg milc n6i tiep voi nhau

K == C ~ D3; D4; Ds; D6 milc n6i tiep voi nhau

Ve so d6 rnach di~n:

1 2x}-----,

7 8B..-.-(8)----@- --®--®---- M

5 6 3 4

u = UBD = UD7 + Uzis + UD3 + UD4

= 6 + 3+ 1,5 + 12 = 22,5(V)

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N

Clnrng minh c6ng thirc thftu kinh

~=J.-+J.-~d'= dff d d' d- f

x« 2 tam giac d6ng dang: ss \ PQ va ss \ MN

PQ S' 0' d'-f~--_=_I_=_-MN S\O d'

df -fPQ = _d_--,,:-f:--= df - df + f2MN df df

d-f

~ PQ = ~.MN. Khi d tang ~PQ giam

fd

nen kich thiroc v~t sang tren man nho d~n di.

G9i dien tich v~t sang ilk d~u khi di€m sang 0-F la S,dien tich v~t sang khi di€m sang 0-vi tri moi la S' . Khidich chuyen S ra xa th~u kinh dien tich v~t sang giamdi nen tai vi tri moi dien tich d6 giam 9 IAn.

~'=(:;y =(~J2 =~~~=k

-e d = 3f= 0,45m = dO + 0,3t = f+ 0,3t

2f= 0,3t ~ t = Is.

Can 5. * Cac biroc thi nghiem:

Cho mroc vao c6c voi th€ tich V I' tha c6c vaochau, xac dinh muc mroc ngoai c6c hnl (d9C trenvach chia).

Cho mroc VaG c6c voi th€ tich V2' V3,.. .lai tha c6cVaG chau, xac dinh rmrc mroc ~, ~3""

Khi do phai cho cho mroc phang l~g.

* G9i hn la rmrc mroc ngoai c6c, mt va Vt nrong irngla kh6i hrong va thS tich mroc trong c6c. Phuongtrinh can bang cho c6c co mroc sau khi tha vao chau:o, (l + hn) S = M + m/

19

.A. _ "" •~[y&~TRE _

~D,,(l + h,,)S =M + ~D"

Thay Vt boi cac gia tri v" V2,···

D,,(l + h"I)S = M + ~D"

D" (l + h"2)S = M + V2D"

(1)

(2)

(3)

VAN DE THin su 'CUNvAT LY HIEN DAI. ..

DQc h"" h"" ... tren vach chi a thanh binh.

L~y(3)trir(2)~S = (V2- V;)/(h"2- h"l) (4)

Tir (2) va (4) ~

l_M+~Dn_h _(M+~Dn)(h"2-hnl)_h- D S "I - D (V _ V,) nl (5)

n n 2 I

* Bi~u tlnrc tinh Dc:

GQi h la do cao cua cec, ho la do cao thanh trong cuac6c; r la ban kinh trang, R la ban kinh ngoai cua c6c;V la the tich cua ch~t lam c6c; S, la dien tich daytrong cua c6c. Ta co:

Vo Voh=ho+l,ho =-=-,;S, nr:

R = r +l=l ~ r=l-l;

D _M _ M M (6)c - V - so, + I) - Vo [Vo l]

S ? +1 -Vo(~-IJ;r

GUlP B~N ON T~P (Tiip theo trang 16)

Am=-q~ q=30880(C)

F.n .Cong Gong dien tlnrc hien: A = q'U = 154400 (J)Cau 4. Kh6i luong dAng barn vao kh6i than chi:

m = 1£( (R+Z/ _R2 ).h.P = 58, 7(g)Ap dung cong thirc Faraday:

A mFn tm=-It~tmin =--~tmin :::::4h55.F.n Almax

Cau 5. Xet trong khoang thai gian t, cac electron qua

ti€t dien S diroc clnra trong hinh tru co the tich SVt.

C' dA d' d'A U enoSVtirong 0 ong ien: ¢:::> -[ =--. . P tS

- U E 1¢:::> penov = - = ~ j.J. = --./ peno

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HUaNG NGHIEN cuu MO DUONG CHOMOT QUY LU~T PHO QUAT TRONG

V~TLYPhqm Xuiin Yem, D(li hoc Paris 6.

Bai nay mong gioi thieu mot cong trinh Iy thuy~t CO'

ban ve v~t ly cua giao sir Dam Thanh Son a Dai hocWashington (Seatle, MT) ma tap chi Physics Todaythang 5 nam 2010 de c~p va ca ngoi trong ba bai lientiep, dieu kha hiem, Nhfrng tien dean va k€t qua tinhtoan cua ong cung cong tac vien, goi t~t la nh6m DTSvira diroc hai tlnrc nghiem kiem chirng thanh congoDieu dang chu y la hai thuc nghiern n6i tren n~m ahai thai cue, mot ben voi nhiet dO cue ky 160 (hangtYIAntYdo tuyet d6i K) a Trung tam may gia t6c ionnang tuong d6i tinh (Relativistic Heavy Ion Collider,RHIC), va mot ben voi nhiet dO cue kY nho (mot vaiphAn trieu do K) a Dai hoc Duke. Tuy d6i cue d~nnhu v~y ma hai thuc nghiem deu quan sat duoc motdong chay gAn hoan hao va do hrong duoc do nhot hcua n6: a RHIC khi cho hat nhan cua nguyen nr yangva cham nhau cue manh, va a Dai h9C Duke khi decac nguyen tlr cua Lithium dong lanh cung cue,Dieu nay minh hoa cong trinh phong phu cua nh6mDTS mang tinh ch~t ph6 quat, dap irng voi nhieu h~thong v~t Iy r~t khac biet. No doi hoi cac tac gia phaico mot kien thirc vira sau s~c vira t6ng the, bao trum danganh v~t ly va th~u triet nhieu phuong phap ti~p c~nkhac nhau de d~t dung v~n de, giai thich no thoa dangcung tien doan nhfrng hien nrong moi me, quan sat dohrong duoc boi thuc nghiem. Cong trinh cua nhornDTS mo dirong cho mot loat nghien CUllve nhimg diahat tuong chirng khong chut lien h~ voi nhau (Thuydong hrc hoc, Vii tru va V~t Iy thien van, Sieu day vaHat, Sieu d~n va v~t ly chat dac, Ch~t hat nhan) nhirngmang met d~c tinh chung ph6 quat va CO' ban.Trong cuon "Ky Y~u Max Planck", cong trinh tren diidiroc nha v~t ly Nguyen Trong Hi~n a Dai hQCCaltechnhac d~n trong bai "SV do dac hang s6 Planck", thircth€ nh6m DTS clnrng minh la dO nhot h tY 1~ thuanvoi h, h~ng s6 co ban Planck. H~ng s6 h cua v~t IyIUQ'ngnr, nhu ta bi€t dong vai tro khai ph6ng, viralam n~n mong CO' ban cho khoa hoc vira thu vi, thi~tthuc trong kY thuat va dai song hang ngay, Theo J. A.Wheeler iroc tinh, mot phan ba t6ng san luong kinht€ cua cuong quoc s6 mot hien nay co g6c nguon nrnhfrng irng dung true ti~p cua cong ngh~ hrong nr,

s6 122 THANG 10 - 2013