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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

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)

z=1cm

option 3) 1cm

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The unit of thermal conductivity is :

• Option 1)

$JmK^{-1}$

• Option 2)

$Jm^{-1}K^{-1}$

• Option 3)

$WmK^{-1}$

• Option 4)

$Wm^{-1}K^{-1}$

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)

Mgl

• Option 2)

MgL

• 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
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Screenshot_991.png The pressure on a swimmer 20 m below the surface of water at sea level is -

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
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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
Screenshot_20190219-202144.png

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 = Râ‚Râ‚‚/(Râ‚ - Râ‚‚) = 8/2 = 4cm
15483076501215404924221128546858.jpg
Since during boiling the water is changing in to steam. During change of state teperature will remain same. therefor =0 so C is infinite
1548154795072..jpg

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

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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

Y=60/10^-6/ΔL/1

2×10^11=60/ΔL*10^-6

60/2*×10^11*10^-6=ΔL

ΔL=3*10^-4 m

ΔL=0.3 mm

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