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# Tag Archives: Industrial Goods and Services

## Air and Liquid Pressure

Does air pressure in a capped bottle is different as that of open bottle??

If not and the atmospheric pressure in a closed container is same as that of the surroundings let 1bar at sea level, if i consider a

tube both end open and dip one end in water (like pipette in chemistry lab) and close the other by thumb, water remain

hanged in the tube.. if we say it is because the atmosphere that pushes up on the water in the tube is same as that of remaining air in tube pushing down on the water..won’t the water fall out due to its own weight as the upward and downward pressure is balanced…

Please explain the whole process and compare weight of water with up and down pressure by atmosphere..

Again would liquid ‘ll flow out of a container through a hole in vacuum??

** Asked Shashank Patra**

The Air Pressure in an open bottle is equal to the atmospheric pressure. The pressure inside a closed bottle can be different.

In the experiment described, when the tube is partially filled and the upper end is closed, the water tries to fall down creating a lower pressure above it inside the tube. This creates a pressure difference, the outside pressure greater than the pressure inside and the water can fall only upto the level where the weight of water column is balanced by the force due to difference in pressure created.

See one live demonstrations here

###### Related articles

## Magnetic Velocity

How would I figure out the velocity of a ball at the end of the chain.

For example if I had 4 half inch magnets each one 6 inches apart with 3 quarter inch steel ball behind each magnet.

If the starting velocity of the first ball to hit the magnet is 10mph.

~~~~~~~~~~~~~~~~~~~~~~~

What if i changed the ball size half way through.

For example if I had 4 half inch magnets each one 6 inches apart with 3 1/4 inch steel ball behind the first two magnets and 3 1/8 inch steel ball behind the last 2 balls

Example video to help understand setup

https://www.youtube.com/watch?

## Questions from Class XI Physics

1. two boats moving parallel to each other and nearby are pulled towards each other. name the scientific theorem involved in the above cases. state and prove the theorem.

2. what are beats?name the basic phenomenon due to which beats are produced.two sources of sound are producing waves of frequency v1 and v2 where ( v1-v2) is small. show mathematically that the beat frequency is (v1-v2).

3. a body is projected with a velocity ‘u’ at angle theta with the horizontal. derive the mathematical equation of the path followed by the body and hence find the expression for the horizontal range. how will the horizontal range change if the angle of projection is changed to (90- theta).

4. using expression for pressure exerted by a gas on the walls of container, deduce Avogadro’s law.

5. a monkey of mass 40kg climbs on a rope which can with stand a maximum tension of 600N. in which of the following cases will the rope break:

a) if the monkey climbs up with an acceleration of 6m/s2

b) if the monkey climbs down with an acceleration of 4m/s2

c) if the monkey climbs up with a uniform speed of 5m/s

( ignore mass of rope. take g= 10 m/s2)

6. what is the need of banking of tracks?

7. the absolute temperature of a gas is increased to four times. what will be the change in its root mean square speed?

8. find the expression for apparent frequency observed by a stationary observer when a sound emitting source is approaching towards the observer.

9. a body weighs 63N on the surface of earth. what is the gravitational force on it due to the earth at a height equal to half the radius of the earth.

10. show that the co- efficient of superficial expansion of a rectangular sheet of the solid is twice its co-efficient of linear expansion.

(Posted by Ritika)

(Post your answers now!

## Doubts on Induction Cooker working

I’m studying induction cookers

what would happen if i placed 2 or more induction coils in close proximity (say a cm apart) and turned them all on?

and how exactly do zoneless induction hobs work?

what would be required to negate the undesired effects, if any?

also, why do they have only circular coils? can it be rectangular/ triangular?

Asked Rahul

## An interesting question from electrostatics

Two equal negative charge -q are fixed at the point (0,a) & (0,-a) on yhe y-axis. a positive charge Q is released from rest at the point (2a,0) on the x-axis. the charge Q will execute oscillatory motion how?

Asked Kritika

## Buoyancy

I read in one of my chapters that when a body is immersed in a container of water (kept on a weighing machine which reads ‘W’ at first )the apparent weight lost by the body is equal to the buoyant force, and thus the reading ‘W’ increases.

Then I came across a question like this –

A beaker containing water kept on a weighing machine weighs W. A body of weight ‘w’ is dropped in it. It is floating & experiencing a buoyant force B, then the reading on machine is –

(a)w+W

(b)W+B

(C)W+w-B

(d)W

please give me the answer and explanation

the book says answer is (a)

but I think it is (c)

(Anwesha posted this questions)

###### Answer

The answer is A.

The total force acting downwards is W+w and the weighing scale is providing an equal reaction. the normal reaction offered by the weighing scale is what we get as the reading.

therefore the reading on the weighing scale must be **W+w**

The buoyant force is acting on the object dropped and is not contributing to the normal reaction offered by the weighing scale.

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## Light, Time and Vacuum

Why does the light needs time to travel through vacuum?Is there something makes it needs time? How did we prove that there is nothing in vacuum?

Answer:

When there is no medium, there is nothing to oppose the propagation of light and therefore it moves with a constant velocity. All electromagnetic waves including light travel in vacuum with the same velocity (3 x 10^8 m/s). Since the energy is to travel from one point to another, a finite time is also required.

The velocity of light is experimentally determined by many different methods. (Romer’s methos, Fizau’s method, Foucault’s method, Michelson’s method etc.)

When light travels in a medium, whenever light interacts with the matter, the atoms absorb light and are re – emitted and the average speed in a medium will be less than in vacuum. In vacuum, there is no matter t interact and that’s why there light travels with maximum velocity.

(If you remember the structure of atom, most of the space inside an atom is vacuum. The speed of light decreases only when it encounters matter. So, when we consider a particular medium, the speed of light is a constant in it)