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# Tag Archives: measurement

## 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

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## Numerical problem based on screw gauge

When a screw gauge with a LC of 0.01mm is used to measure the diameter of a

wire, the reading on the sleeve is found to be 0.5 mm and the reading on the thimble is found to be 27 division i)what is the diameter in cm?

Posted by Swati

Answer:

Diameter = PSR + CSR x LC = 0.5 +27 x 0.01 = 0.77 mm = 0.077 mm

## A doubt from Dimensional Analysis

What about the correctness about the relation,

s_{t}=u+0.5a(2t-1), both dimensionally or any other

Prakash Adhikari asked

**Answer**

The equation refers to the displacement in the **t ^{th} second** and hence it should have the dimensions of speed; since it is the

**displacement in one second**.

Under this consideration, the equation is dimensionally and otherwise correct.

## A light year is the distance light travels in one year . How many meters are there in one light year?

The speed of light in vacuum is 3 x 10^8 m/s. That means in one second it travels 300000000 metres.

As we know, in one year, there are 365 days; in each day there are 4 hours; in each hour there are 60 minutes and in each minute there are 60 seconds.

Therefore, the distance traveled by light in one year = 3 x 10^8 x 365 x 24 x 60 x 60 = **1 light year = 9.4605284 × 10 ^{15} meters**

## A Question from Errors in measurement

An experiment measures quantities a,b and c, and X is

calculated from

if the percentage error in a,b,c are ±1%, ±5%, ±2% respectively, the percentage error in X will be

a) 7%

b) 5%

c) 1%

d) 9%

Answer:

Percentage error = 1x percentage error in a + 2 x percentage error in b + 3 x percentage error in c

= 1×1 +2×5+3×2

=1+10+6

= 17%

SO there could be a misprint in the question posted by you.