Physics Times 07.2019

1.1. 2. 3. 4. 5. c 2. a 3. d 4. d 5. d

1.Sol: Rate of vaporization of water^20

g

hr



Water vaporized in

2hr 40^40

1000

 g kg

Given that^540

L

C

C

 

Heat looses by water = Heat gained for

vaporization

(m m C T mL  )

( )

m m T mL

C

  

0.04

540 5.4

(4 0.04)

T C

 
    
  
2.Sol: A lunar eclipse can occur only on the night
of a full moon.
3.Sol: When the exoplanet reaches the line that joins
the star and earth then energy (power) emitted
by the star will be absorbed by the planet P. So
the intensity of radiation that reaches the earth
decreases.

4.Sol:

The initial intensity at the earth in the absence of

the planet is

(^42)
I P
r

The intensity at the earth in the presence of
planet is
(^22)
' 0.9999
'
4 4
P P
I
 r r
 
The effective area of the sun that emmits
radiation is 4 (100 ) 4 R R^2  ^2
(^) I' 0.9999 I
1.Sol:
2.Sol:
3.Sol:
4.Sol:
When an object is seen through a water filled
cylinder then inversion takesplace along
horizontal direction and no inversion takes place
along vertical direction as shown in the figure
A and C on vertical line so they are not inter
changed but A gets horizontally reversed, which
can’t be recognized. C gets horizontally inter
changed, as shown in the figure
Similarly B and D positions get interchanged but
they are reversed horizontally as shown in the
figure
So the correct image is (d).
5.Sol:5.Sol: Given that
(^1) ( ) 2
2
v x  for x 0
Acceleration of the particle is
2
2 ( )
d x dV
x
dxdt
  

2
2
( )
( )
d x
x
dt



 
The above equation represents SHM with time
period
(^1)
T^2  2 sec

 
T 1 is independent of energy
2
(^1) ( )
2
V k x  for x 0
Acceleration of the particle is
2
2 ( )
d x dV k x
dxdt
  
2
2 ( ) ( )
d x k x
dt
   
The above equation represents SHM with time
period
(^2)
T 2 2
k
 

 
T 2 is independent of energy
The correct graph should be (d)