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A soap bubble , having radius of 1 mm is blown from, a detergent solution having a surface tension , of 2.5 \times 10 ^{-2 } N/m. The pressure inside the bubble equals at a point Z_0 below  the free surface of water in a container of water = 10 ^ 3 Kg / m ^ 3 , the value of Z_0 is 

  • Option 1)

    100 cm 

  • Option 2)

    10 cm 

  • Option 3)

    1 cm 

  • Option 4)

    0.5 cm 

GIVEN : surface tension = force /length = 0.025 N/m

radius = 1mm = 0.001m

p(final) - p(initial) = 4t/r

where z is a pressure inside the bubble 

p(z=final) - p(initial) =pgh =pgz = 4t/r

pgz = 4t/r

z = 4t/pgr

z = 4(0.025)/(0.001)(1000)(10)

z =0.100/10

z = 0.100(0.1)

z = 0.01

z= 1(0.01)


option 3) 1cm


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The unit of thermal conductivity is : 

  • Option 1)


  • Option 2)


  • Option 3)


  • Option 4)


Option 1)Option 2)Option 3)Option 4)

A small hole of area of cross sectyion 2 mm ^ 2 is  present mear the botom  of a fully  filled open tank  of heiht 2 m . Taking g = 10 m /s ^2 , the rate of flow of water through the open hole would be nearly : 


  • Option 1)

    12.6 \times 10 ^{-6 } m^3 / s

  • Option 2)

    8.9 \times 10 ^{-6 } m^3 / s

  • Option 3)

    2.23 \times 10 ^{-6 } m^3 / s

  • Option 4)

    6.4 \times 10 ^{-6 } m^3 / s

  Option 1) Option 2) Option 3) Option 4)

When a block of mass M is suspended by a long wire of length L , The length of the wire becomes (L+l ) . The elastic potential energy stored in the extended wire is : 


  • Option 1)


  • Option 2)


  • Option 3)

    1/2 Mgl

  • Option 4)

    1/ MgL

 Option 1)Mgl Option 2)MgL Option 3)1/2 MglOption 4)1/ MgL

A copper rod of 88 cm and an aluminium rod of unknown length have their increase in length independent of increase in temprature . The length  of aluminium rod is : 

(^\alpha C_u = 1.7 \times 10 ^{-5} K^{-1} \: \: and \: \: ^ \alpha A1 = 2.2 \times 10 ^{-5}K^{-1})

  • Option 1)

    6.8 cm 

  • Option 2)

    113.9 cm 

  • Option 3)

    88 cm 

  • Option 4)

    68 cm 

For Copper  L = 88 cm    Option 1) 6.8 cm  Option 2) 113.9 cm  Option 3) 88 cm  Option 4) 68 cm 
A cable that can support a load w is cut into two equal parts. find maximum load that can be supported by either part of wire is
load supported by the cable is directly proportional to the breaking stress. Breaking stress = F / A  F is the force and A is the cross-sectional area. As we see that the breaking stress is independent of the length of the cable. So, if the cable is cut in two equal parts, the maximum load that can be supported by either parts of the cable remain the same as before.  
Screenshot_991.png The pressure on a swimmer 20 m below the surface of water at sea level is -

3 atm is right answer

The ideal black body is : (1) Hot coal at high temperature (2) Surface of glass printed with coal tank (3) Metal surface (4) A hollow container painted with black colour


 hot coal at hight temperature as any solid object which has been heated above ambient temperature, is scientifically refered to as a “Black Body”. 

IMG_20190305_133258.jpg As compared to the person with white skin. person with black skin will experience (1) Less heat and more cold (2) More heat and more cold (3) More heat and less cold (4) Less heat and less cold
More heat and more cold because black object absorbs all wavelengths of light and converts them into heat, so the object gets warm. A white object reflects all wavelengths of light, so the light is not converted into heat and the temperature of the object does not change noticeably.
Screenshot_20190305-001643.png A circular plate of radius 4cm and weight w is made to rest on one surface of water. if a minimum force is needed to clear the plate from water surface. Then find F. Given Sw=0.072 N/m
@Firoz For a circular plate the force required is F = 2 π R  * Sw     as the interface between the water, plate and air is a circle of radius R

A solid sphere of radius R made of a material of bulk modules B is surrounded by a liquid in a cylindrical container. A massless area A floats on the surface of the liquid . When a mas M is placed on the piston to compress the liquid, find fractional change in the radius of the sphere

@Lakhan When mass M is placed on the piston, the excess pressure , P = Mg/A. As this pressure is equally applicable from all the direction on the sphere , hence there will be decrease  in volume due to decrease in radius of sphere.  Volume of the sphere, Differentiating it , we get                        ∴                   ΔV/V =  3ΔR/ R       We know that, or,                     ΔR/R =...

IMG_20190221_115536.jpg 38. The length of an elastic string is x meter when the tension is 8N and y meter when the tension is 10 N. The length in metre when the tension is 18 N is

stress=youngs modulas*strain  8/A=Y*(X-L)/L....................(1) 10/A=Y*(y-L)/L....................(2) 18/A=Y*(Z-L)/L....................(3)  (1)/(2) solving we get L =5X-4y  (3)/(2)    9y-9L=5Z-5L eliminating L Z=5y-4X

The apparent coefficient of expansion of liquid when heated in a copper vessel is c and when heated in a silver vessel is s .If A is the linear cofficient of expansion of copper then the linear cofficient of expansion of silver is :

for copper; for silver;
the temperature gradient in rod of 0.5m long is 80 degree centigrade per metre.if the temp.of hotter end of rod is 30 degree cntgrades,then the temperature of the colder end is? @vijay 
The temperature of the colder end can be calculated by using this formulae: 
two SOAPS bubbles of radii 2 cm and 4 cm join to form a double bubble in air then radius of curvature of interface is.?
When a smaller bubble and a bigger bubble come in contact then  Radius of their interface = R₁Râ‚‚/(R₁ - Râ‚‚) = 8/2 = 4cm
Since during boiling the water is changing in to steam. During change of state teperature will remain same. therefor =0 so C is infinite

assume that solar constant is 1.5 KW /m^2. Radius of sun is 7*10^5 Km and the distance of earth from center of the sun is 1.5*10^8 Km. Stefans constant is 5.67*10-8Wm-2K-4.  find the approximate temperature of sun

@Mahima power emitted by the sun  using  find value of T

In a calorimeter of water equivalent 20 g ,water of mass 1.1 kg at 288 k temperature .if steam at teperature 373 k is passed through it and temperature of water increase by 6.5 degree c then the massss of steam condensed is

Let x be the mass of steam condensed. The heat obtained calorimeter with water is equal the heat from condensing x kg of steam and the heat from cooling x kg of water to the final temperature of calorimeter with water      
1548067539635..jpg A solid cube is first floating in a liquid. The coefficient of linear expansion of cube is alpha and the coefficient of volume expansion of liquid is gamma. On increasing the temperature of (liquid + cube) system, the cube will sink if
  In the question as the cube is initially just floating the density of the cube=density of water Afterwards when the temperature is increased ; The increase in volume of water is proportional to The increase in volume of cube is proportional to the volume expansion coefficient of cube I.e So for water Vfinal =Vinitial .(1+) For cube Vfinal =Vinitial.(1+) (V is volume) So as the mass is...
IMG_20190118_135204.jpg (7) Two parallel and opposite forces, each 4,000 N are applied tangentially to the upper and lower faces of a cubical metal block 25 cm on a side. Find the angle of shear and the displacement of the upper surface relative to the lower surface. Shear modulus for the metal is 80 GPa. (4)A mass of 2 kg is suspended from a steel wire of length 1 meter to form a pendulum arrangement. Of the mass is moved to one side and released from the horizontal position of wire then find the maximum extension in the length of the wire.

velocity at lowest position =√2g=√2*10=√20 m/s        ,∴g=10m/s^2

now force at lowest position F=mg+0.5mv^2/r=2g+2*20/1=  2*10+40  = 20+40    = 60 N




ΔL=3*10^-4 m

ΔL=0.3 mm 


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