# Physics :: Bubble Problem

A water drop of surface tension T=0.07N/m and have mass m=0.2gram is placed two glass plates. The distance Between them is 0.01 cm .Find the Force of attraction between the plates ?

A)-2.8N

B)-3.5N

C)-0.7N

D)-1.25N

Thanks

Note by Karan Shekhawat
3 years, 2 months ago

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yep answer is 2.8 N, The only tricky thing here is to find pressure difference inside the approximately cylindrical bubble , let me show you with a diagram

The concept is just as Raghav told

but i dont know hot to upload images (forgot )

so till you tell that, consider the equations

Total force due to surface tension

= 2*2.S.pi.R (the extra two since there are two contacts at two plates)

where R is NOT the radius of curvature but the radius of the approximately cylindrical drop

and effective area =2.pi.R.H (the curved surface of cylinder

(where H is the distance between the plates

so pressure = force/area = 2S/H

i suppose now you can proceed

(Note- the likely mistake is to assume that this works just as a bubble and use 2S/R and then claim logically 2r=h and get 4S/H )

(here R is the radius of curvature )

the reason it doesnt work is because the curved surface is not spherical (yes , it matters)

- 3 years, 2 months ago

And Just a little query .. what % marks are you getting in JEE advance Test's in ur coaching or in any Test series or etc... And what is your Target (I know there is time to strenghten our Practice and concepts... but still what are Probabble guess according to Tution Test's or any Test Seriees Based test's .... ?)

- 3 years, 2 months ago

Around 250 is good score for me, in coaching tests I m facing some problems with chemistry otherwise I m comfortable with P and M.

ALL THE BEST Raghav, Karan, Mvs for advanced :D

- 3 years, 2 months ago

I want to get $$300+$$ out of $$360$$. Or it's equivalent in whatever the total marks we have this year. Yeah, it is a bit high, but I want it. Also, my current percentage in coaching institute is nowhere near goal.

- 3 years, 2 months ago

i want the same, i am doing whatever i can for it, let us see what happens ,

- 3 years, 2 months ago

That's great.. Best of luck for ur goal ... ! Btw how much you got in ur Last exam in ur coaching ...?

Also is Shashwat and you both are in same Institute ? Since I saw that you are from same city .. am i right ?

- 3 years, 2 months ago

We are classmates man, for the last two years.

- 3 years, 2 months ago

Just curious ... How much he genrally get in tution ...?

- 3 years, 2 months ago

It's high enough for other people to be bothering themselves with it. If you know what I mean.

- 3 years, 2 months ago

And It is great , I mean 300+ means you are Planing To get Below Air 25 .... am I right @Raghav Vaidyanathan

- 3 years, 2 months ago

Thanks... you both @Mvs Saketh @Raghav Vaidyanathan ... I got it !

- 3 years, 2 months ago

Can we the maximum distance between plates so that water is in contact with both plates?

- 3 years, 2 months ago

ideally, it is infinite, no matter how far you take, the water column will become thinner and thinner but still wet both sides till it becomes negligibly thin far far away, but ofcourse not really

- 3 years, 2 months ago

Look at the figure. The force is due to the excess pressure outside as compared to inside the water droplet. We can calculate the pressure difference. We can also calculate the area of contact by approximating the shape as a cylinder. Then just multiply to get force.

- 3 years, 2 months ago

Looks similar to Einstein rosen bridge :p

- 3 years, 2 months ago

This thing is correct. I will post solution. @Karan Shekhawat

- 3 years, 2 months ago

If you are referring to an AIITS problem by FIITJEE, most of my friends are of the opinion that it is wrong.

- 3 years, 2 months ago

No It is not from AITS ... And I 100% Sure that this is correct one ... But I did not posted exact language ... So wait I'am Posting Question as It , again with data and options also ... So that you can match it ...

Btw what was AITS Question ...? Please tell

- 3 years, 2 months ago

Yes, please post original problem. A similar question appeared in AI2TS. Let's see.

- 3 years, 2 months ago

I have posted it... Please do check it ..

- 3 years, 2 months ago

- 3 years, 2 months ago

can you double check data?

- 3 years, 2 months ago

Yes I had Posted same to same wording of Question .. as it is.. !

btw , What answer do you getting ?

what is concept in this question...

- 3 years, 2 months ago