2. 12
12.1
- F
( F F F F F F F
)
- F F F F F
F F F F F
F F F F F F
F F F
F
F
1. F
N1 A0 N1
A1 A1 N2
N2
A2 A2
N3 N3 F ( )
F
F F ( ) F
A3
A3
s1 s2
2. F
F F F
F A
C>B>A
A B C
F F www.schoolDD.com 1
3. 3. F F
F F F F
F F F F F
F F F
F F
4. F
F F F F
F F F
F F F
F F F
F
12.2
- F F F F
- F (T v
Ff )
- ( vt ) t
vt = 331 + 0.6t -50° C ≤ t ≤ 80° C
vt
v
F FF F F F F
F F F
F F www.schoolDD.com 2
4. F (v) F
v=f
v= (m/s)
f= ( / Hz)
= (m)
12.3 F
F
F
F
F
F
. F F F
. F F F
F F
F F www.schoolDD.com 3
5. . F F F
F F F F F F
. F F
F F
F
- f F F
F 1
F F F F F
F F F2 F F F F
F 1500 m/s
s= vt
v = 1500 = 1500 (2/2)
t=2
s = 1500
s= 1500 m Ans
F 2
F 25˚ C 35˚ C F
F vt = 331 + 0.6t
t = 25˚ C , v25 = 331 + 0.6(25) = 331 + 15 = 346 m/s
t = 35˚ C , v35 = 331 + 0.6(35) = 331 + 21 = 352 m/s
= 352-346 = 6 m/s Ans
F F www.schoolDD.com 4
6. F 3
F F F F F
F F F 6.0 cm F F F F
340 m/s
F F F F
F F 6.0 cm
v=f
f= = = 5.67x103 Hz Ans
F 4
F F F F F 2 2 4
F F 340 m/s
t1 =2 t2 =4
s1 s2
s1 s2 s = vt
s1 = vt1 = 340(2/2) = 340 m
s2 = vt2 = 340(4/2) = 680 m
F F s = s1 + s2 = 340 + 680 = 1020 m Ans
12.4 F F
F I F F F F
F FF (W/m2)
P= (Watt)
R
s I= R= F F s
F F
P FI
F F www.schoolDD.com 5
7. F F F (dB)
I= F F
= 10 log I0 = 10-12 W/m2 F F
F F
2
Imax = 1 W/m F
F F
- F FF F
- F F
F
f
- F ( Tr ) F 60 dB
60 dB
0 t
Tr
F 5
22 F F F F
F 140 F
R = 140
ss P = 22
F I= =
F F www.schoolDD.com 6
8. I = 1x10-4 W/m2 Ans
F = 10 log
= 10 log
= 80 dB Ans
F 6
F A B F F 50 100 F A F
-2 2
F 4x10 W/m B F F F
RA = 50 IA = 4x10-2
A
F
B IB = ?
P
RB = 100
F I=
P I
=
IB = IA = 4x10-2
IB = 1x10-2 W/m2 Ans
F 7
F F F F F F
F F 1 W/m2
F = 10 log
= 10 log = 10 log 1012
= 10 x 12
= 120 dB Ans
F F www.schoolDD.com 7
9. 12.5
F (f ) F
F F F F 20 20,000
Hz F 20 Hz F F F 20,000 Hz F
F F F
F
F F
20 20,000 Hz
F F www.schoolDD.com 8
10. - F 2 F F F
C 256 Hz F C 256x2 = 512 Hz F
F F, F F
f , 2f , 3f , , nf ( F ) F F F F
F F F F F
F F F F
F
F F F 1
F F F F
F F 2 F 3 2 3 F
( f , 2f , 3f , , nf )
F F F
nf , In nf , In nf , In
f , I1 f , I1 f , I1
3f , I3 3f , I3 3f , I3
2f , I2 2f , I2 2f , I2
- F F F F f,I n F
F 8
F 350 Hz F 1, 2, 3 4
F 1, f = = 350 Hz
F 2 , 2f = 2(350) = 700 Hz
F F www.schoolDD.com 9
11. F 3 , 3f = 3(350) = 1050 Hz
F 4, = = Hz
12.6 F
F F
- F
- F F
F F F F F
F F F
F
F F F
F F F F F
F
F F www.schoolDD.com 10
12. F 9
F F F 680 Hz F
340 m/s F 1 , 2, 3 F
F
F f = 680 Hz v = 340 m/s
= = = 0.5 m
s1 = ?
F
s1 = = = 0.125 m Ans
F s2 = + = = = 0.375 m Ans
s2 = ?
F
F 10
F F F F F
1.0 m F 340 m/s
F F
FF = F
= 4x1 = 4 m
f F f= = = 85 Hz Ans
F 11
F F F F F F F
F F F F F 2 F F F
F 10 cm 2 F 20 cm F F
340 m/s
F F www.schoolDD.com 11
13. 0.20
0.10
- = 0.20 0.10 = 0.10
= 2x0.1 = 0.2 m
f F f= = = 1700 Hz Ans
12.7 F
F F F F F F
F F F
F F F F
f1 = F 1
Δ f = | f2 f1 | f2 = F 2
∆f ≤ 7 F F
F 12
F F 2 F F F 514 Hz 510
Hz
F Δf = | f2 f1 |
= | 510 514 |
Δf = 4 Hz Ans
F F www.schoolDD.com 12
14. 12.8 F F
F F (Observer) F F
(Source) F F
s
F F
1. F F
vt vt v=
vs t vs = F
vO = F
fs = F
fO = F F
F
O = F F
F F F F
=
F O =
fO = =
F F F
=
F O =
fO = =
F F www.schoolDD.com 13
15. 2. F F F
v
s F
vO vO
F F F F F
f=
F fO =
=
fO =
F F F F
f=
F fO =
=
fO =
F F
F F
fO = fs
F F
1. F F F ( vO = 0 ) F fO = fs
- F F FF F fO F fO = fs
- F F FF fO F fO = fs
- O F O =
F F www.schoolDD.com 14
16. 2. F F F F ( vs = 0 ) F fO = fs
- F F F F fO F fO = fs
- F F F fO F fO = fs
- F =
3. F F F F F F 1 2
F 13
1000 Hz F 340 m/s
F F
. F 40 m/s F F F F F
. F 40 m/s F F F
. F F 10 m/s F
. F F 10 m/s
F
F F fO = fs
fs = 1000
v = 340
vO vO
vs F
. vs = 40 m/s F , vO = 0
fO = fs
= 1000 = 1000
fO = 1133 Hz Ans
. vs = 40 m/s , vO = 0
fO = fs
= 1000 = 1000
fO = 895 Hz Ans
F F www.schoolDD.com 15
17. . vO = 10 m/s F , vs = 0
fO = fs
= 1000 = 1000
fO = 1029 Hz Ans
. vO = 10 m/s , vs = 0
fO = fs
= 1000 = 1000
fO = 970 Hz Ans
12.9
F F F
F
F
F
s
F F F
F F F F F
F F F F F
F F www.schoolDD.com 16
