Hướng dẫn giải chi tiết đề thi tuyển sinh đại học, cao đẳng môn vật lí phần 2 tờ số (26)

Ta

: x, =

C O

X ,

=> k,.!, = k , . i , <=> k 1

k
A,
5
= k , A . =>—!- = - i = _ .
" "
k,
>i,
4

Co 4 v a n s a n g Xi v a 3 v a n s a n g A.2.
Vdy chon

dap

Cdu

T o n g hgrp h a t n h a n h e l i

19:

an

[ H + j L i - ^ jHe + X .

A.

M6i phan

jHe

ufng t r e n

tOf p h a n i J n g h a t

toa

nang

liTong

17,3

nhan
MeV.

N a n g liTdng t o a r a k h i t o n g hgfp dUdc 0,5 m o l h e h l a
A . 1,3.10'" M e V .

B. 2,6.lO'" MeV.

C. 5 , 2 . 1 0 ' " M e V .

D. 2,4.10'" M e V .

Giai
H a t n h a n X c u n g l a h a t H e n e n so p h a n ufng b a n g m o t nijfa so h a t .
T a c o : E = 1 7 , 3 . ^ = 2,6.10^'
2
Vdy chgn
Cdu

20:

dap

an

MeV.

.
B.

M o t s o n g a m v a m o t s o n g a n h s a n g t r u y e n tii k h o n g k h i

vao nifdrc t h i bi/dfc s o n g
A . cua s o n g a m t a n g con bUo'c s o n g cua s o n g a n h s a n g g i a m .
B . cua s o n g a m g i a m con btTo'c s o n g ciia s o n g a n h s a n g t a n g .
C. cua s o n g a m v a s o n g a n h s a n g deu g i a m .
D . cua s o n g a m v a s o n g a n h s a n g d e u t a n g .

Giai

V a n toe t r u y e n a m t r o n g ni/o'c t a n g , v a n toe t r u y e n s o n g a n h s a n g
t r o n g nu'd'c g i a m m a t a n so k h o n g d o i .
Vdy chon
Cdu

21:

dap

an

A.

T r o n g gior thiTc h a n h , m o t hoc

sinh mac

doan mach

AB

gom d i e n t r d t h u a n 4 0 Q, t u d i e n c6 d i e n d u n g C t h a y d o i dtrgfc v a c u o n
day C O do t U c a m L n o i t i e p n h a u t h e o d u n g thuf i\i t r e n . G o i M l a d i e m
n o i giufa d i e n t r t f t h u a n v a t u d i e n . D a t v a o h a i d a u d o a n m a c h

AB

m o t d i e n a p x o a y c h i e u c6 g i a t r i h i e u d u n g 2 0 0 V v a t a n so 50 H z . K h i
dieu c h i n h d i e n d u n g cua t u d i e n d e n g i a t r i Cm t h i d i e n a p h i e u d u n g
giufa h a i d a u d o a n m a c h M B d a t g i a t r i

CLTC

t i e u b a n g 75 V . D i e n t r d

t h u a n ciia c u o n d a y l a
A . 24 D.

C. 30 Q.

B . 16 Q.

D . 4 0 Q.

Giai
D i e u c h i n h C de
T a c6:

U M B

Vdy chon

ULCmax-

= U , = 75V

dap

an

K h i do x a y r a c o n g h i i d n g .
U R

= 125V , R = 4 0 Q

=> r =

24Q

A.

Giai Chi t I e t d S thi T S D H , CD M o n vat li

,

159


Cdu 22: K h i n o i ve song dien tCf, p h a t bieu nao sau day la s a i ?
A . Song d i e n tCr m a n g nang lifc/ng.
B. Song d i e n tCf t u a n theo cac quy luat giao thoa, n h i e u x a .
C. Song d i e n tii l a song ngang.
D. Song d i e n tCr k h o n g t r u y e n di/Oc t r o n g chan k h o n g .

Giai
Chgn dap an D.
Cdu 23: K h i n o i ve sii t r u y e n song co t r o n g m o t m o i triio'ng, phat
bieu nao sau day dung?
A. Nhurng p h a n tuf cua m o i trtfdng each nhau m o t so nguyen I a n
biTdtc song t h i dao dong cung pha.

B. H a i p h a n tuf ciia m o i trtfo'ng each nhau m o t p h a n tu hitdc song
t h i dao dong lech p h a nhau 90°.
C. NhuTng p h a n tuf cua m o i trifc/ng t r e n cung m o t hiidfng truyen song
va each nhau m o t so nguyen I a n

hiXdc

song t h i dao dong cung pha.

D. H a i p h a n tuf ciia m o i t r i i d n g each nhau m o t nufa hxx6c song t h i
dao dong ngiitfc pha.

Giai
Chgn dap an C.
Cdu 24: D i e n n a n g tCr m o t t r a m p h a t d i e n dtroc di/a den m o t khu
t a i d i n h cir b k n g difofng day t r u y e n t a i m o t pha. Cho biet, neu dien ap
t a i dau t r u y e n d i t a n g t\i U l e n 2 U t h i so ho d a n diJOc t r a m cung cap
du dien n a n g t a n g tii 120 l e n 144. Cho rang c h i t i n h den hao p h i t r e n
di/6'ng day, cong suat tieu t h u dien ciia cac ho d a n deu nhxi nhau, cong
suat cua t^am p h a t k h o n g doi va he so cong suat t r o n g cac triio'ng hop
deu bang nhau. N e u dien ap t r u y e n d i l a 4 U t h i t r a m p h a t huy nay
cung cap du d i e n n a n g cho
D . 192 ho d a n .

C. 504 ho dan.

B. 150 ho dan.

A. 168 ho dan.

Giai
•

B a n dau: P N = 120Po + Php
1
1
K h i U t a n g 2 I a n t h i Php g i a m 4 I a n : P N = 144Po + - Php
Suyra:P„^=32P„
K h i U t a n g 4 I a n t h i Php g i a m 16 I a n : P,,,, = 2?^
Ta c6: 32Po - 2Po = 30Po (cung cap t h e m di/Oc 30 ho).
Vqy chgn dap an B.

160

Giai C h i trSt de t h i T S B H , C D M 6 n Vat l(


Cdu 25: Tren mot sgri day cang ngang vdi hai dau co dinh dang c6
s o n g dCtog. Khong xet cAc diem bung hoac nut, quan sat thay nhuTng
diem c6 cung bien do va of gan nhau nhat t h i deu each deu nhau 15cm.
B L T O C song tren day c6 gia t r : bang
A. 30 cm. .
B. 60 cm.
C, 90 cm.
D. 45 cm.

GiSi
Cac diem c6 cung bien do deu each deu nhau t h i each nhau mot
khoang — = 15cm. Suy ra: X = 60 cm. Vdy chon dap an B.
4

Cdu 26: TOf mot tram phat dien xoay chieu mot pha dat t a i v i t r i
M, dien nang di/gfc truyefi tai den ncfi tieu thu N , each M 180 km. Biet
dirdng day c6 dien t r d tong cong 80 Q (coi day tai dien la dong chat, co
dien trd t i le thuan vdi chieu dai cua day). Do sir co, difdng day bi ro
dien tai diem Q (hai day tai dien bi noi tat bdi mot vat co dien trof co
gia t r i xac dinh R). De xac dinh v i t r i Q, trtrdfe tien ngUofi ta ngat
diiofng day l ^ o i may phat va t a i tieu thu, sau do dung nguon dien
khong doi 12V, dien trof trong khong dang ke, noi vao hai dau cua hai
day t a i dien t a i M . Khi hai dau day t a i N de hof t h i ci/dng do dong
dien qua nguon la 0,40 A, con khi hai dau day tai N difofc noi t a t bdi
mot doan day co dien trd khong dang ke t h i ciTofng do dong dien qua
nguon la 0,42 A. Khoang each MQ la
A. 135 km.
B. 167 km.
C. 45 km.D. 90 k m .

Giai

12
Luc dau (Rd nt R) ta co: Rd + R = —
0,4
Luc sau [Rd nt (R // 80 - Rd)] ta co: R, +

(1)
Rf80 —R )
K + oU —Kj

R
Giai (1) va (2) ta c6: Rd = 20; R = 10 =^

12

-—

U, 4z

(2)

X

= — ^ X = 45km.
80 180

Vdy chqn dap an C.
Cdu 27: Dat dien ap u = Uocoscot (V) ( U Q khong doi, co thay doi
dirgfc) vao hai dau doan mach gom dien t r d thuan R, cuon cam thuan
4
CO do tir cam — H va tu dien mSc noi tiep. Khi co = coo t h i CLfcfng do
571

dong dien hieu dung qua doan mach dat gia t r i
dai I ^ . K h i co = coi
hoac CO = C 0 2 t h i cifdng do dong dien eiie dai qua doan mach bang nhau
C L T C

va bang Im. Biet coi - C O 2 = 2OO71 rad/s. Gia t r i cua R bang
A. 150 Q.

B. 200 Q.

Gi4i Chi tiet de thi TS DH, CO M6n vat If

C. 160 Q.

D. 50 Q.
161