Bài tập vật lý luyện thi đại học

Bài tập vật lý luyện thi đại học
Câu 1: !
"#$%&$'()*+,- !
.(/01&$2$./'
3
4
.".5'%./66)*6!738938 !:3
8+;1&$./9'
3
4."
<=<>?
A.
@3V
B.
@3
7
V
C.
A@3
A7
V
D.
A33
AA
V
Giải:
Giải:
;'
;'
A
A

B'
B'
3
3
,."- !CDB
,."- !CDB
9
AA
9
A
EF
CLR
UUU −+
B@3F8E
B@3F8E


GD
GD
A
A
B738HD
B738HD
'A
'A
B938HD
B938HD
A
A
B:38IIIIIJK

B:38IIIIIJK


B9HK
B9HK
'A
'A
B
B
7
9R
;1'
;1'
9
9
B9'
B9'
3
3
IIIIIJK
IIIIIJK
'9
'9
B9K
B9K
'A
'A
B
B
7

LR
+;%(2
+;%(2
KB
KB
9
9
9
EF
CL
UZR −+
B
B
99
E9
7
L
F R
R
R −+
B
B
7
A7


Điện áp hiệu dụng hai đầu điện trở bằng U
R2
=
Z

U
R =
A7
A@3
V. Đáp án C
V. Đáp án C
Baì 3:M9NO !P.AQ-.2R6S%
T%0*")*UTVB93WX+P
T%6!3LYT+ZG"!Q>-.%U)[
& \OP !.OP6!+P=]G%9N"
\<>&+^./SR26!
A. A:L:+ B. 9A_L+ C. 9L@:+ D. 77Q@+
GiảiCP)\T%CλB YVB339B9
^$T5<N`2T%OP
^$T5<N`2T%OP


O
O
B
B
A
A
T
T
ω
ω





P
P
B
B
9
9
TF
TF
ω
ω
abE
abE


cdN>GOB"
cdN>GOB"
A
A
HPB"
HPB"
9
9
e%(*fOP
e%(*fOP


O
O
B

B
A
A
TF
TF
ω
ω
I
I
λ
π
A
9 d
E
E


P
P
B
B
9
9
TF
TF
ω
ω
abI
abI
λ

π
9
9 d
E
E
" \<>&0
" \<>&0
O
O
 !
 !
P
P
"U
"U
b
b
I
I
λ
π
9
9 d
a
a
λ
π
A
9 d
B90

B90
b
b
IIIIIJIIIIJ"
IIIIIJIIIIJ"
A
A
g"
g"
9
9
BF0I
BF0I
9
A
E
E
λ
λ
IIIIIJ"
IIIIIJ"
A
A
g"
g"
9
9
B9F0I
B9F0I
9

A
EB90IA
EB90IA
FhE
FhE
;N=>OP4%"
;N=>OP4%"
A
A
g"
g"
9
9
B90gA
B90gA
"
"
A
A
a"
a"
9
9
BAQFE
BAQFE
IIIIIJ"
IIIIIJ"
A
A
B0aQ@

B0aQ@
eN" \<>&>OPC3i"
eN" \<>&>OPC3i"
A
A
B0aQ@iAQ
B0aQ@iAQ
IIIIIJIQ
IIIIIJIQ
≤
≤
0
0
≤
≤
_+M>OP%AQN" \<>&
_+M>OP%AQN" \<>&
IIIIIJ)[&&2OPR00B3 !0BA+
IIIIIJ)[&&2OPR00B3 !0BA+
,N]G%9N" \<>& \%./SR
,N]G%9N" \<>& \%./SR
4 !G6!N" \<>&C` \0BIAHG
4 !G6!N" \<>&C` \0BIAHG
` \0B9
` \0B9
;U \C0BIAIIIIJ"
;U \C0BIAIIIIJ"
A
A
g"

g"
9
9
BI7IIIIIIJ"
BI7IIIIIIJ"
9
9
g"
g"
A
A
B7FhE
B7FhE
M%"
A
9
B
9
a@
9
"
9
9
B
9
aA7
9
G%"
9
9

g"
A
9
BALLIIIIIJF"
A
a"
9
EF"
9
g"
A
EBALLFhhE
MfFhE !FhhEIIIIJ"
A
a"
9
B
LQFhhhE
LQFhhhE
MfFhE !FhhhE"
MfFhE !FhhhE"
A
A
B99@
B99@


9
9
B"

B"
A
A
9
9
g@
g@
9
9
BLQA9@F
BLQA9@F
9
9
E
E
> h = 21,9374 cm. Chọn đáp án B
> h = 21,9374 cm. Chọn đáp án B
Bài 4:66)*<`%<)\T%
A
λ
B:33 !
9
λ
B37
m
µ
 !R
064j)*.kl% #&66)*6!
A
B9+A3

@
YT !
9
B
L+A3
@
YT+<=<`%<)\T%
7
λ
B39
µ
4 j&2k
56!
O+@+A3
@
YTP+9
m
+A3
@
YT+
:
+A3
@
YTG+:+A3
@
YT
GiảiC
••
Wn
P

"
9
"
A

O
G


•
M%C
A
λ
hc
BOao
A
FAE
9
λ
hc
BOao
9
F9E
7
λ
hc
BOao
7
F7E
G

9
B9
A
IIIIIIJo
9
BLo
A
FAEIIIIIJL
A
λ
hc
BLOao
9
FApE
'RFApEgF9EHL
A
λ
hc
I
9
λ
hc
B7OIIIIJOB
7
hc
F
A
L
λ
I

9
A
λ
EFLE
o
7
B
7
λ
hc
IOBF
7
A
λ
I
A
7
L
λ
a
9
7
A
λ
EB
79A
7A799A
7
L7
λλλ

λλλλλλ
+−
FhE
o
A
B
A
λ
hc
IOBF
A
A
λ
I
A
7
L
λ
a
9
7
A
λ
EB
9A
9A
7
λλ
λλ
−

FhhE
MfFhE !FhhE
A
7
đ
đ
W
W
B
79A
7A799A
EF
L7
λλλ
λλλλλλ
−
+−
Bm
IIIIIJ+
A
7
v
v
B
m
 > v
3
= v
1
m

= 2
m
.10
5
m/s. Chọn đáp án B
Bài 5+,N$.>)["#$A3364q.r
.6><>6+P=sTRr>0s(.>
)["#$U \"t>"# !<$.
>)["#<=A3u.\.
O+_3AP+Q__+Q@A@G+_A9@
Bài giảiC^vw6!sTRr>)["#
sTRx0)q.∆w
A
 !T0q.∆w
9

∆w
A
B
9
A
9
A
R
P
U
8\w
A
Bwa∆w
A

Hw
A
By
A
+D
A

∆w
9
B
9
9
9
9
R
P
U
8\w
9
Bwa∆w
9
+
,$>)["#0)q.∆DBy
A
B3AD
A
IIII
B
A
9

A
A3
P
U

9 9
A A 9 9 9
9 9
9 9 A A A
A33 A3
P P U U P
P P U U P
∆
= = ⇒ =
∆
w
A
Bwa∆w
A
w
9
Bwa∆w
9
Bwa33A∆w
A
Bwa∆w
A
I3__∆w
A
Bw

A
g3__∆w
A
-0.%∆w
A
Bw
A
9
9
A
U
R
=
= w
A
9
9
A
A
9
A
A3
U
P
U


B3Aw
B3Aw
A

A
G%
G%
A
9
U
U
BA3
BA3
A
9
P
P
BA3
BA3
A
AA
__3
P
PP ∆−
BA3
BA3
A
AA
A3+__3
P
PP −
BA3+FAI33__EB_3A
BA3+FAI33__EB_3A
Vậy U

2
= 9,01U
1
Chọn đáp án A

Bài 6+z$0626r%06)*B3A0xkBA3
Im

)*l<=T*"#0s{$.%"!6r%
v)[B_QYT
9
 !)*-)[=%
)[|B9+A3
:
8Y+P)[]k$NT*"#%)rZ
` s% \)r2)[<s} \ j<<=
3+'&q2"#0k$k /x#<=\6!C
O+A39~+P+A3L~++A7:~+G+A7_~
Giải: ;68MP\np"#l* \)r
Z`%•
3
C•
3
B
P
F
B
mg
Eq
B

_Q3
93
B393L3
•
3
B393A9F"E
'&q2"#0k$k /x#<=\)*./
ls`MBpF7g9T•
3
E
r"pB
99
ag +
FB
m
Eq
B9YT
9
E
pB
99
9Q_ +
BA3339YT
9
+
7g9T•
3
B7g9FAg9T
9
9

3
α
EBAaLT
9
9
3
α
EBAa
9
3
α
IIIJT = mg’(3 – 2cosα
0
) = 0,1.10,002(1 + 0,2012
2
) = 1,0406 N = 1,04N. Đáp án B
Bài 8:9OP)*"l)r s% \-)\+
^vy6NOP !~6!9NyP.y66)*6!
mA3+M[N j6!€7
7
FYTE4 j~6!<>?
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Bài 9 :RN[">n%)r4
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Bài 10."#0s$ \
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M[N
A
2RN%./&N+M[N
9
B
A
aŠ
F%
9
i93A7ME42RN6!A3b
9
YT+^./6\R2Š

6!
A. L39Lm@T+ B. L39L9@T+ C. L39@9@T+ D. L39@m@T+
Giải: 04"MB
ω
π
9
B9T
^%./&NCB30 jk8MPIIIJB3
B93TFb
A
I
:
@
π
EB3IIIIJFb
A
I
:
@
π
EB‰
9
π
a0
9
π
IIIIIJ
A
B
:

@
‰
9
A
a
9
k

A
B
7
A
T
BI93bTFb
9
I
:
@
π
EBA3b
9
IIIIIJTFb
9
I
:
@
π
EBI
9
9

IIIIIIIIIIIIIIIJ

9
B
A9
m
a90 !p
9
B
A9
A_
a90+f
9
i93A7MBL39:FTE

9
B
A9
m
a90iL39:IIIIJ0≤93A9Hp
9
B
A9
A_
a90iL39:IIIIJ0≤93A9

9
B
A9
A_

aL39LB
A9
LQ73m
FTE
Do đó giá trị lớn nhất của ∆t là∆t
max
= t
2max
– t
1min
=
A9
LQ73m
-
7
A
= 4025,25 (s). Đáp
án C
Bài 13:W66t j%06)*L0 !6t
%`A33~Y+W6)*-T.<>T9"F‹
6!.6tE)*6!U !=+Mf8MP0d jl
)r26t Ux>L !<s}0sU6Œ+
vB36![N<s jFAE+M[N$<s jF9EN"2F9E
 \FAE%<>"&%N6!C
A. bYA3T+ B. 7bYA3T+ C. 9bY@T+ D. B7bY@T+
GiảiC04"2•6C
MB9b
k
m
B9b

A33
L
B3LbFTE
,N"2 j9 \ jA%<>"&4[<s
j90 jA /x<>#`6![NBF90aAE
9
T
BF90aAE+39b+
G%[N$<s jF9EN"2F9E \FAE%<>"
&%N6!Ct =
@
7
π
( ứng với k =1. Đáp án D
Bài 14C0jN>sTRAL9Q_o%."
0!<4)["6!9938+,
2"#$frR0jN6!+;0jN0s"U
.<.N."20!<4)[4
"rR6!7@_80%`[9"#
20jNbY:T \"t`[v+;0j
N"U.<.6x)%1T~
A
Y~
9
BA@N."20
! Ž<4)[)00s"U.<.4
"rR6!F<TsTRTrR2.<
.<=AEC
O+A:@L8P+773_8+L_:78G+::A:8
Giải:

;0s"U.<.C)["tkR0
jN‹x6!"tk)["#$
yB
ϕ
TU
P
B
:
T993
AL9Q_
π
Bm@FOE
,T.>)["#ŠD
A
BD
A
IDByIIIIJB
I
UU −
A
B
m@
9937@_ −
B
m@
A7_
•
;"U.<.C,."rR6!D
9
BŠD

9
aDp
Dp6!.TrRDpBD
9
9
N
N
BA@DB7733F8E
,T.>)["#ŠD
9
Byp \yp6!)["tkTr
RC
ypBy
9
A
N
N
B
A@
I
B@FOEIIIIIJŠD
9
BypB@+
m@
A7_
B_9mB_7F8E
Do đó U
2
= ∆U
2

+ U’ = 3309,3 (V). Chọn nđáp án B
Bài 15:)[/<f>D
A
BAA386>9938
\6•0s#.0sR.q6)* !."#%R
S \T t.` \A9 tY8s+~)[%Œ!!
`R)6)*] t2TrR+;5
. \`R)*D
9
B9:L8T \TrRŒ>0
.6!D
A
BAA38+e t"#</)*6!C
O93PAA+A3G99
Giải:^vT t."#2POlŒ>6!~
A
 !~
9
M%
⇒==
9
A
993
AA3
9
A
N
N
~
9

B9~
A
FAE8\~
A
BAA3A9BA79 t
^v6!T t"#</)*+;%%

9:L
AA3
9
9
9:L
AA3
9
A
A
9
A
=
−
⇒=
−
N
nN
N
nN
F9E
M~
A
BA79 t4)*BAA t+Chọn đáp án B

Chú ý: Khi cuộn sơ cấp bị cuốn ngược n vòng thì suất điện động cảm ứn xuất hiện
ở các cuộn sơ cấp và thứ cấp lấn lượt là e
1
= (N
1
-n)e
0
– ne
0
= (N
1
– 2n) e
0
với e
0

suất điện động cảm ứng xuất hiện ở mỗi vòng dây.
e
2
= N
2
e
0
Do đó
9:L
AA3
99
9
A
9

A
9
A
9
A
9
A
=
−
⇒===
−
N
nN
U
U
E
E
e
e
N
nN
Câu 16CM>-)\%.T%0*6!NO !P.
73"l)r4
O
B
P
BT93b+<>T%
0s(k.4T%+~)[)*0$.]
N`>6>>OP6!7+cd9N
A

 !
9
>OP
.NW2OP]66)*6!3@ !9+M[N
A

j2
A
6!gA9YT4 j2
9
6!
O+L
@
YTP+LYT+7
9
YTG+L
7
YT
GiảiCM%<)\T%λB97B:+
cdN>OP.WCWB"HOPB73
e%fOPC
O
BT•93bI
λ
π
E
9
F9 d
AB
+

‚

P
BT•93bI
λ
π
E
9
F9 d
AB
−
‚


B
O
a
P
B9T
λ
π
d+9
TF93bI
λ
π
AB+
EB9T
7
+d
π

TF93bI@bE


Bp

BIL3bT
7
+d
π
TF93bI@bEIIIIJ
A
9
M
M
v
v
B
7
T
7
T
A
9
d
d
π
π
B
:
T

7
9
T
π
π
BI
7
A
IIIIJv
M2
= -
7
A
v
M1
= 4
7
cm/s. Đáp án D
Câu 17CWT%0*>-)\e
A
e
9
" \)r4C
A

BTFωE
9
BTFωEe
A
e

9
B_λ+,NR>&2e
A
e
9
"
U \
A
.e
A
e
9
<>+
O+L@λYQP+7_λYQ+L7λYQG+LAλYQ
Giải:
M%

A
BT…BTFωI
9
π
EH
9
BTFωE
cdN>&2e
A
e
9
C
e

A


Be
9
B"F"‘L@λE

A
BTFωI
9
π
I
λ
π
d9
EH
9
BTFωI
λ
π
d9
E


B
A
a
9
BTFωI
λ

π
d9
I
9
π
EaTFωI
λ
π
d9
E


B9TF
L
π
ETFωI
λ
π
d9
I
L
π
E
,N"U \
A
C
λ
π
d9
a

L
π
I
9
π
B90πIIIIIIIJ"BF
Q
A
a0Eλ
"BF
Q
A
a0Eλ‘L@λIIIIIIJ0‘L7m@IIIIIJ0‘@IIIIIIJ0

B@
d
min
=
Q
LA
λ . Chọn đáp án B

•
e
9
•
e
A
•
•

y
Câu 18:W
A
B7
3
 !
9
B:
3
+~< \%
TR|B:8N. ! \"#
$'!"f&"+;"t"
&4)[&2
9
+W&>"#
2"T%6!
O+78P+9
7
8 +7
9
8 G+9
:
8
Giải;,"2<B9
3
+,x2<z
3
B|BA9
3
~q6)*<2o

3
B
C
Q
9
9
3
B7:
3
;By
3
IIIJo
'
B
9
9
3
LI
B7:
3
~q6)*20%o
A
Bo
9
B3
e0
9
"2"pB7
3
W&>"#2"T%‹x6!

&]<$&2
A
C
9
9
3
LI
B
9
9
A
UC
IIIIIJ
9
7
9
3
UC
B7:
3

IIIIIJU
max
= 2
:
V
 Chọn đáp án D
Câu 19CM>-)\%.T%0*6!NO !P.
73"l)r4
O

B
P
BT93b+<>T%
0s(k.4T%+~)[)*0$.]
N`>6>>OP6!7+cd9N
A
 !
9
>OP
.NW2OP]66)*6!3@ !9+M[N
A

j2
A
6!gA9YT4 j2
9
6!
O+L
@
YTP+LYT+7
9
YTG+L
7
YT
GiảiCM%<)\T%λB97B:+
cdN>OP.WCWB"HOPB73
e%fOPC
O
BT•93bI
λ

π
E
9
F9 d
AB
+
‚

P
BT•93bI
λ
π
E
9
F9 d
AB
−
‚


B
O
a
P
B9T
λ
π
d+9
TF93bI
λ

π
AB+
EB9T
7
+d
π
TF93bI@bE


Bp

BIL3bT
7
+d
π
TF93bI@bEIIIIJ
A
9
M
M
v
v
B
7
T
7
T
A
9
d

d
π
π
B
:
T
7
9
T
π
π
BI
7
A
IIIIJv
M2
= -
7
A
v
M1
= 4
7
cm/s. Đáp án D
Câu 20: MN>-R6S%"l)rZ
` \TA93WKT%(/>-)\+cdN
~F~B3@E>-R6S= x \ >)r
T%6s"U+e*6xRkT.&>~6!L+M
T%>-R6S6!C
O+A@YTP+93YT+A9YTG+A3YT

GiảiC
G~"U>~B0λ+e*6xR0~k /x
#<Z
;%~B0λBLλIIIIIJλB~YLB3A9@
Do đó tốc độ truyền sóng trên mặt chất lỏng là: v = λf = 0,125. 120 = 15m/s.
Đáp án A
Câu 21
66t%T%>ωB9@"YTr&"!6tZ
` j-<>")\+~06% jL9YT4>6t</]
6+Mx j&26+
O+:3YTP+@QYT+m7YTG+:mYT
GiảiC;r&"6t.0s</<"F.0sv
6)*E+'Œ j% #
3
BL9YT4>6t</]6 jT„"
k8MP \T%ωB9@"YTH8MP. /x2 j6Œ6t
)*]6!

3
B∆6B
k
mg
+
8j&26)*./ls`C
9
9

mv
B
9

9
3
mv
a
9
EF
9
lk ∆
IIIIIJ
9

v
B
9
3
v
a
m
lk
9
EF∆
8\ωB
m
k
IIIIIIJ
m
k
B
9
A

ω
 !∆6B
k
mg
+B
9
ω
g
B
9
A333
ω
FE
9

v
B
9
3
v
a
m
lk
9
EF∆
B
9
3
v
a

9
EF
ω
g
BL9
9
a
9
E
9@
A333
F
BL9
9
aL3
9
B77:L
IIIIIIJv
max
= 58 cm/s. Chọn đáp án B
Câu 22+66tZ`"&"+P>0$[
"’•66t</d ! lr jU<=33@bFTE
!b
9
BA3+8j&2 jl<=?
O+ALALYTP+A3YT+93YTG+ALALYT
GiảiCM"t0$["’ lr j !
U` \0$[ jNf<>8MP`6!f
•
~

•

<#FIOEn-f<>")rOn !B
L
T
+G j%
L
T
B
33@bIIIIJMB39bIIIJωBA3"YT
;$[6t</d<=B
L
T
>[ jNf6B
IŠ6<>BIO6!
A
BY9B
Q
T
M[ jfv6BIŠ6
6!
L
T
I
Q
T
B
Q
T
>Š6B

9
9A
 \O6!<>2"
-0.Š6B
k
mg
B
9
ω
g
B3ABA3IIIIIJP>"OB
9
9 l∆
B
9
93
B
A3
9

Vận tốc c]c đại của vật treo v = ωA = 100
9
cm/s = 1,414 m/s. Đáp án khác
Câu 23CWT%0* !~.93><-R6S"
l)rZ`UU<>O%T9@WX
T%AYTl<>0s(k.4T%+eN>
)[t-ZR6Sj~6!)[0x%<>"
<=OY9+
O+7:P+L9++L3+G+7Q+
GiảiCP)\T%λB YVB33LBL

eN" \<>&9OFT<T%EC
IA3≤0
9
λ
≤A3IIIIIJIA3≤90≤A3IIIIIIJI@≤0≤@M>~%AAN"
 \<>&0N$ !~+^]N60" \<>
&LO%9N" \<>OY9+M~%93N"
 \<>OY9++Do đó trên đường tròn thuộc mặt phẳng chất lỏng nhận
MN làm đường kính có 20x2 = 40 điểm có biên độ dao động bằng A/2. Đáp án C
Đõ Viết Doanh Toại
Câu 24C66t)*-=6t%`0B@3~Y !
j-06)*B933+; j /x#<=4."6&ƒ
0s("vl26t !%6\6!9~0$[3AT+
PSkvT.6RBA3YT
9
Hb
9
BA3+c./&2 jT0
6&ƒf."?
O+93bYT+P+93b
9
YT++9@bYT+G+L3bYT+
GiảiC
MT%266tCωB
m
k
B
93
@3
B@

A3
B@b"YT
G)\."26&ƒ j"N. /x#<=
3
B
k
F
B33L
BL
! j)* jCŠ Bƒ+ŠIIIIIJŠ B B
m
tF∆
BAYT
P>2"T06&ƒf."CO
9
B
3
9
a
9
9
ω
v
B333@:F
9
E
IIIIIIJA = 2
AL
cm+Tốc độ c]c đại v
max

= ωA = 10π
AL
cm/s. Đáp án khác????
.$2% Rl6
M !<G%N0$.6!")\!
^vn6! /x6t0s</<"n
A
6! /x#<q0%6&ƒ."
P>"0%6&."ƒ6!OBnn
A
P>O)*xC,;#<=0OBƒ
cmm
k
F
A L3L3
@3
9
====→
046
s
k
m
T L39 ==
π
e3AT)r`6!MYL 4 jf /x<>.nNTMYLT„ \
/xn
A
 #6Œ!6! B
A
ω

\ /x!f6&."4 /x#<=
\266! /xn+P>"\6!C
9L9
EF
“
9
9
9
9
9
9
==+=+= A
A
A
v
xA
ω
ω
ω

M&C
scmA
m
k
Av Y993““

πω
===
Câu 25:6rt<S<=06)*xkJ3+;-
6 !)[% dr)[)[=4

 /x#<="#l* \)rZ`%α%αB7YLH
6Œ!6"S \0”M
A
+~()[!T
dr)[")[%)rZ`)\6> !)[0s
(40”"S266Œ!6!C
A.
A
M
@
+ B. M
A
m
@
+ C. M
A
@
m
+ D. M
A
@
+
^$
;)[|%)r46&)[%)r
ƒ k| 7 L
 T
w  L @
α = = = => α =
6" \"
" A

"
 @ L
 M 9 9 +
T L   @
= = => = π = π
α
l l

FAE
n
9
n n
A
;)[)\6>46&)[)\6>6" \
"
k| k| 7 
  FA E FA E
  L L
= − = − = − =
"
+L
M 9 9 F9E
 
=> = π = π
l l
'RFAEF9E
A
M M @=
vG
#C9:

Một con lắc lò xo đặt nằm ngang gồm vật M có khối lượng 400g và lò xo có hệ số
cứng 40N/m đang dao động điều hòa xung quanh vị trí cân bằng với biên độ
5cm. Khi M qua vị trí cân bằng người ta thả nhẹ vật m có khối lượng 100g lên M
(m dính chặt ngay vào M), sau đó hệ m và M dao động với biên độ
A.
9 @cm
B. 4,25cm C.
7 9cm
D.
9 9cm
Giải
Khi M về vị trí cân bằng thì vận tóc của M là:
A
M
k
Av +==
ω
Khi vật m nhỏ đặt lên M thì đây là va chạm mêm nên tốc đọ của vật là
mM
Mv
V
+
=
đậy của là tốc độ c]c đại của M+m
Nên:
cm
mM
k
mM
A

M
k
M
V
AAV @9
A33L33
@+L33
E+F
+
“
“““+ =
+
=
+
+
==→=
ω
ω
Câu 27C"#0s$ \
%.
3
+ Tu U c t
ω
=
F8E4"tT\r.6!
A
ϕ

.""#6!738+P=<=
“

 7=
4
"tjr.6!
9 A
9
π
ϕ ϕ
= −
 !."
"#6!_38+P>
3
?U =
O+
:3V
+ P+
73 9V
+
:3 9V
+ G+738
^$C
D
"A
B73F8ED
"9
B_3F8EIIIIJ
A
9
d
d
U

U
B7IIIIJy
9
B7y
A
IIIIIJK
A
B7K
9
IIIIIII+K
A
9
B
_K
9
9
IIIIIIJ
9
aFK
'
gK
A
E
9
B_
9
a_FK
'
I
7

AC
Z
E
9
IIIIIJ9F
9
aK
'
9
EBK
'
K
A
FhE
9 A
9
π
ϕ ϕ
= −
IIIIIJϕ
A
aϕ
9
B
9
π
IIIIIJϕ
A
ϕ
9

BIAF 4ϕ
A
i3E
ϕ
A
B
R
ZZ
CL A
−
Hϕ
A
B
R
ZZ
CL 9
−
B
R
Z
Z
C
L
7
A
−
R
ZZ
CL A
−

R
Z
Z
C
L
7
A
−
BIAIIIIIIJFK
'
gK
A
EFK
'
I
7
AC
Z
EBI
9
IIIIIIIJ
7
9
a7K
'
9
gLK
'
K
A

a
9
Ac
Z
B3IIIIIIIIJ7F
9
aK
'
9
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Câu 28
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d
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điệu biên độ, tức là làm cho biên độ của sóng điện từ cao tần (sóng mang) biến
thiên theo thời gian với tần số bằng tần số của dao động âm tần. Cho tần số sóng
mang là 780kHz. Khi dao động âm tần có tần số 1kHz th]c hiện một dao động
toàn phần thì dao động cao tần th]c hiện được số dao động toàn phần là:
O. 780 P. 390 . 1560 G. 195
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1
và n
2
là số dao động toàn phần sóng mang và sóng âm th]c hiện
trong thời gian t
t = n
1
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1
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2
T
2
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A
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s  %  \  n+  P  )r  4  "    2    j  6  6)*  6!
( )
A
LT L 7x t cm
π π
= +
 !
( )
9
L 9 T L A9x t cm
π π
= +
+Mxf[N
A
A 9Lt s=

[N
9
A 7t s=
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Sr
9 7 cm
6!<>?
A.

A 7 s
B.
A Q s
C.
A : s
D.
A A9 s
Giải :
L = x
2
- x
1
= 4
9
Cos( 4πt +π/12) - 4 Cos( 4πt +π/3) = 4 Cos( 4πt -π/6) cm
2
7
cm
Coi đây là một vật dao động điều hòa.
Thời điểm t
1
= 1/24s vật có li độ x
01
= 4cm
Thời điểm t
2
= 1/3 s vật có li độ x
02
= - 2
7

cm
Khoảng thời gian vật chuyển động Δt = t
2
– t
1
= 7/24s
Góc quét trong thời gian Δt là α = 4π. 7/24 = 7 π/6
Thời gian khoảng cách giữa hai vật không nhỏ hơn 2
7
cm
Nghĩa là tổng thời gian khoảng cách giữa hai vật lớn hơn hoặc bằng 2
7
cm
Có Cos›B2
7
/4 =
7
/2 Suy ra ›Bπ/6
Thời gian quét góc ›6!Δt
0
= π/6.4 π = 1/24s Trong khoảng thời gian từ t
1
đến t
2
có khoảng thời gian khoảng cách giữa hai vật lớn hơn 2
7
cm là t = 3. Δt
0
=
3.1/24= 1/8 s Đáp án B

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n6! /x#<=2ŒEk.4"RN0s 
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1
=10Cos( 4πt
+π/3)  ! x
2
= 10
9
Cos( 4πt +π/12)cm+WRN.@[N
>0Nf6Œ
3t =
6!
A.
A Q s
B.
A _ s
C.
@ 9L s
D.
AA 9L s
L = x
2
- x
1
= 10
9
Cos( 4πt +π/12) - 10Cos( 4πt +π/3) = 10Cos( 4πt -π/6) cm
Với L = 5cm
Coi đây là một vật dao động điều hòa.

Thời điểm t
1
= 0 vật có li độ x
01
= 5
7
cm
Có Cos›B5
7
/10 =
7
/2 Suy ra ›Bπ/6
Có Cosα = 5/10 = 1/2 Suy ra α = π/3
Thời gian chuyển động t = (βaα)/ω = π/2.4 π = 1/8 s
Đáp án : A
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m@v cm s=
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aD

E
9

BD
9
a7D
9
BLD

9
IIIIJD
O
aD

B9DIIIIJ9D

B9D
IIIIIJU
C
= U = 220V. Đáp án C
Hoặc khi ta có Z
C
= Z
AM
suy ra U
C
= U
AM
tam giác OU
AM
U là tam giác đều >
U
C
= U = 220V
#7:CxœI# .T.0l}e[7
<ŒrT%<)\T%6AB7_9H
9
λ
BL_3H

7
λ
Bm7@+M>!
0$ #T.6>% ##kT.)*
<> T.rT` \<`69?
O+AAP+_+mG+:
P•y^yžy+
Bài 1
• ;
A
λ
A
B0
9
λ
9
BJ
A9
A@
L
@
A
9
9
A
===
λ
λ
k
k

• ;
7
λ
7
B0
9
λ
9
BJ
A9
Q
7
9
7
9
9
7
===
λ
λ
k
k
'j<$CNRT&U2. #T.+
;
A
3@A3A@
;
9
37L:Q_A9
;

7
39L:Q
~) j #T.6>% ##%AA #
T.2λ
9
)%@•U \λ
A
 !λ
7
>%: T.rT
` \<`λ
9
+,ŸwŸ~G
Câu 37C<"#$'
!+,- !.%./"DB
A338 !TV0s(+,1NB
A
B@3•4sTR>2
6!w
A
B:3o !%62. !"t6!ϕ
A
+,1NB

9
B9@•4sTR>26!w
9
 !%62. !"t
6!ϕ
9

 \T
9
ϕ
A
aT
9
ϕ
9
B
L
7
M1T
A
9
P
P
<=
O+AP+9+7G+L
Giải: w
A
BDy
A
Tϕ
A
By
A
9

A
IIIIIJy

A

A
BDTϕ
A
IIIIJy
A
B9Tϕ
A
FAE
w
A
BDy
A
Tϕ
A
B9DT
9
ϕ
A
IIIIIJT
9
ϕ
A
B
U
P
9
A
B

A3
7
F9E
w
9
BDy
9
Tϕ
9
By
9
9

9
IIIIIJy
9

9
BDTϕ
9
IIIIJy
9
BLTϕ
9
F7E
T
9
ϕ
A
aT

9
ϕ
9
B
L
7
IIIJT
9
ϕ
9
B
L
7
IT
9
ϕ
A
B
L
7
I
A3
7
B
93
_
FLE

A
9

P
P
B
A
9
I
I

A
9
T
T
ϕ
ϕ
B
A
9
T9
TL
ϕ
ϕ
A
9
T
T
ϕ
ϕ
B9
A
9

9
9
T
T
ϕ
ϕ
B9+
A3
7
93
_
B7+Chọn đáp án C
Câu 38CPNn~U=>5)[ZR.fn+Mn
-N.T%#Z)\0ss)[0sR
#+`)[#6!m3"P~6!73"P+~N#%
T /x4`)[#N~0%6!
O+7:A"P+P+LA9"P++77L"P+G+L9A"P+
GiảiC^vw6!sTR2#
yB
9
L R
P
π
'

g'
~
B6
N
M

I
I
B6F
OM
ON
E
9
BmgLB7
6
OM
ON
BA@IIIIIJn~B7A:9nIIIJ~Bn~gnBn~FAI
:97A
A
EBn~
:97A
:973
'
W
g'p
~
B6
N
H
I
I
“
B6F
MH
MN

E
9

B969B3:39PFhE
'p
~
g'
~
B6
N
N
I
I“
B6F
MN
ON
E
9
B96
:973
:97A
B339QPIIIIIJ'p
~
B'
~
a339Q

B739QP
FhhE
L

H
= 3,028 + 0,602 = 3,63 B = 36,3 dB. Đáp án A
Câu 39C`q6)*>5s)*./<=<N`|BI
9
:A7
n
Fl8E \∈~h.r<$` \BA+.0xs
.0xx !l6lk "f~+M1T]<)\T%"!
R !R!.0x>%N.0N ."f%
`q6)*Rr6!
O+A:Y_+P+A_9Ym++A7@Ym+G+L+
GiảiC

λ
hc
B|
~
g|
;
B|
L
g|
A
BA7:FAI
A:
A
EBA7+:+
A:
A@



λ
hc
B|
~
g|

B|
L
g|
7
BA7:F
_
A
I
A:
A
EBA7+:+
_+A:
m
>


λ
λ
=
m
A7@
. Đáp án C
Câu 40:66tk$SxkBa@+A3

I@
FE !6t
%`0BA3~Y"t \<>@>-Z=
0sT.+M[Nk$k /x#<= !% j)\
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k$T0%)[ !"&2k$)\0%
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7
+ C.
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D. 7+
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Av
ω
=
8/x#<=\.8MP‹CBk|Y0B@+A3
I@

+A3
L
YA3B@
P>\C
9@“
9
9
9
=+=
ω
v
xA

M1TxC
9
““
==
A
A
v
v
Câu 41:MxœI# .T.0l}e.[7
<`rT U.T.4R%<)\T%66)*
A 9
3L9 H 3@:m m
λ µ λ µ
= =
 !
7
λ

 \
7
λ
J
9
λ
+M>!0$] #T.
#\ #T.l%!! #T.#R%9
T.6!T&U2 #T.
A
λ
!
9
λ
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2 #T.
A
λ
!
7
λ
+P)\T%
7
λ
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3m:¡+ D. 3:@¡
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9
A

L
L
7
λλ
λ
λ
=→=
9 #T.U! \ #T.#%%7 #U
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#)rŒ70$ #
8#"!29 U!##
a
D
L
A
L+7
λ
=
aT U2<`A !76!@)r`L0$ #CLB'
n
m
=
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A
λ
λ
6!#TT$
7L+7L
AA
→==→

a
D
a
D
n
λλ
mm
m
µλλ
λ
λ
:739m@3@:3H
7
77
A
7
=→=→<<=→
Câu 43:.N \Sr2v)[
r-.+M.%6r"t+04
"260.N$@uT \04"
260.`>+8dr2.
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9
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9
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g
l
T
π
9=
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g
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→=−→=
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Câu 44:P6rU06)*l !! \m9
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A
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9
+ B. 6
7

+ C. 6
A
+ D. 6
L
+
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04"2!6!
MB
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93
@A9
==
v
S
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g
l
T
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9
B3@9_THM

7
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L
B3+:_9T
eT.04"26! \04"246
%" \<>6\R
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Câu 45:c6! ")\@308>"tyBA
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9+A3N
=
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A. WBQ3u B. WB
AA
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−
C. WB3Qu D. WB33m_@u
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7A3
Q7LA7
==→
−
−
H
Câu 46:Mx \<!kN"j"tk
)[$"U{%./798+M.U}l6l
k !)\% !f)[%PB7+A3
g@
MT j2
l6l s% \
B
r
+P.0xk 6\R2.l6lk6!C
A. L3 B. L C. 93 D. 9
^$C

P.0xk£6\R2l6l` \&2l
a
h
Umv
=
9
9
A
P.0xk£
cm
eB
mU
mBe
eU
m
Be
mv
R
hh
93
A3+:A+A3+7
97+A3+A_+9
9
+
+9
+
A_@
7A
≈====
−−

−
Câu 47:,-.%BDTF‡E8 !
% !$%$'PD'
0s(1V4R0VBV
A
4."•5
'66)*6!938L38:38;VB9V
A
4.$6!
O+93P+L9+Q3G+:L
GiảiC;VBV
A
%D
'
B9D

HD

B7D

IIIII+K
'
B9HK

B7 !%DB93
9
8
;VB9V
A
4K

'p
B9K
'
BLHK
p
B
9
C
Z
BA@IIIJD
'p
BLD
H
D
p
BA@D
p
IIIIJD
9
BD
9
p
aFD
'p
gD
p
E
9
Bm9@D
9


III+D
p
BA3@8IIIII+U
L’
= 4U
R’
= 42V.
Đáp án B
Câu 48COPO \$
%&$6()*+,P \
%"+,- !OP.(/B
D
9
TωF8E4"0.K

26\R76+;'B'
A
4
."]O%./<=D
A
 !.`[
]OP6%ϕ
A
T \"t+;'
B'
9
B9'
A
4."]O%./<=D

9
B
3@D
A
 !.`[]OP6%ϕ
9
T \"t
+W`6>]ϕ
A
 !ϕ
9
6!C
O+ϕ
A
Iϕ
9
B_3
3
P+ϕ
A
aϕ
9
B_3
3
ϕ
A
aϕ
9
B:3
3

G+ϕ
A
Iϕ
9
B:3
3
Giải:D
A
B
9
A
9
99
E7F RZR
ZRU
L
C
−+
+
B
9
A
9
E7F
A3
RZR
UR
L
−+
Hϕ

A
B
R
RZ
L
7
A
−
D
9
B
9
9
9
99
E7F RZR
ZRU
L
C
−+
+
B
9
A
9
E79F
A3
RZR
UR
L

−+
Hϕ
9
B
R
RZ
L
7
9
−
B
R
RZ
L
79
A
−
D
9
B3@D
A
IIIIJ
9
A
9
E79F
A
RZR
L
−+

B
9
A
9
E7F
@3
RZR
L
−+
iBBBJK
'A
B9@
ϕ
A
B
R
RZ
L
7
A
−
BI3@HIIIIJϕ
A
BI9:@:@
3
ϕ
9
B
R
RZ

L
79
A
−
B9IIIIJϕ
9
B:7L7@
3
> ϕ
2
- ϕ
1
= 90
0

Câu1:.<%TRQ3u+TrR%A@3 t`R%
733 t+W`R \"#%A33Ω
&$7AQW+WTsTRTrR<=A+WTrR)*-
%D
A
BA338T@3WX+Mx)["Tr
R+
A. AQO B. 93O C. A@O D. 9@O
hD
9
BD
A
+~
9
Y~

A
B9338
h¤`RCK
'
BA33K
9
B
99
L
ZR +
BA33
9
HTϕ
9
BAY
9
Hy
9
BD
9
YK
9
B
9
FOE
hM%WBw
9
Yw
A
B3QBJD

9
y
9
Tϕ
9
B3QD
A
y
A
Tϕ
A
BJy
A
B9@O ,ŸwŸ~G
P!9.AR%VB:3WK~
s2%<=s0.%r-& !VB:3WK4T
tk2s[(m933 tT-2s<6!
O+A3P+L+A@G+@
hM%CVB
A
Y:3B:3BJ
A
B7:33Y
h!CVB
( )
A
:3
9
+p
n

H \
9
B
A
I
:3
m933
B
A
IA93F tYŒEFV0s(BJT-
&q4$E
BJ:3B
( )
A
:3
A93
A
+
−
p
B
( )
A
:3
A937:33
+
−
p
BJ
9

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P!7 !"#`R2.<.6x) !
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"#ŒN6!AA38~"#` !
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