Physics Times – July 2019

4. Assertion:The flash of lightening is seen
   before the sound to thunder is heard.
   Reason: Speed of sound is greater than speed
   of light.


5. Assertion:Sound travels faster in solids than
   gases.
   Reason: Solid possessses greater density than
   gases.


6. Assertion:

Reason:

5. Assertion:

Reason:

WAVES ON STRING

1. a 2. d 3. a 4. d


2. a 6. b 7. c 8. a

SOUND WAVES

1. c 2. a 3. c 4. c 5. b

WAVES ON STRING

SOUND WAVES

WAVES ON STRING

1.Sol: As,

(^350) 0.7
500
v m
n
  
3 rad

 As,
2
x

 

0.7 60 0.12 12
2 180
    x    m cm
  
2.Sol: Every small segment is acted upon by
forces from both sides of it hence energy is
not conserved, rather it is transmitted by the
element.
3.Sol: For the propagation of transverse waves,
medium must have the property of rigidity.
Because gases have no rigidity, (they do not
possess shear elasticity), and hence transverse
waves cannot be produced is gases. On the
other hand, the solids possess both vlolume and
shear elasticity and likewise bith the longitudinal
and transverse waves can be transmitted
throught them.
4.Sol: At node v = 0, at antinode Tension to
velocity
 at both the points power = 0 (P F v  )
 
At other points P0.
6.Sol: In stationary wave, total energy associated
with it is twice the energy of each of incidence
and reflected wave. Large amount of energy
is trapped with the waves. Hence, there is no
transmission of energy through the waves.
7.Sol: The equation of stationary waves is
20sin cos
4
x
y t

 
Compare with y a kx t2 sin cos
4
k


(^28)
/ 4
  m

Distance between two consecutive antinodes
(^84)
2 2
   m
8.Sol: If the soldiers while crossing a suspended
bridge march in steps, the frequency of
marching steps of soldiers may match the
natural frequency of oscillation of the
suspended bridge. In that situation resonance
will take place, then the
amplitude of oscillation of the suspended bridge
will increase enormously, which may cause the
collapsing of the bridge.
SOUND WAVES
1.Sol: Sound waves are mechanical waves
2.Sol: Sound waves require material medium to
travel. As there is no atmosphere (Vacuum)
on the surface of moon, therefore the sound
waves cannot reach from one person to
another.
3.Sol: The velocity of sound in a gas is directly
porportional to the square root of its absolute
temperature as.
v RT
M
  
  
 
Since temperature of a hot day of more than
cold winter day, therefore sound would travel
faster on a hot summer day than on a cold
winter day.
4.Sol: Speed of light is greater than that of sound,
hence flash of lightning is seen before the
sound of thunder.
5.Sol: Sound wave required medium.
WAVES ON STRING
1.Sol:
2.Sol:
3.Sol:
4.Sol:
6.Sol:
7.Sol:
8.Sol:
SOUND WAVES
1.Sol:
2.Sol:
3.Sol:
4.Sol:
5.Sol: