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# Monthly Archives: April 2014

## photodiode sensor

i want to make a sensor using photodiodes. here photodiodes are connecting parallel and to each photodiode i have to put a load resistance. how can we calculate the value of photo diode? on what basis we can design the load resistance value. i am applying a voltage of 2.5 volt . Is there any method for finding the load resistance value of a photo diode ?

## Nature of Electromagnetic Waves

When we represent the frequency, amplitude, and wavelength of any electromagnetic radiation on a graph we see a wave like in water. Is this just a geometric representation or do the “packet” aspects of these waves actually move physically like the mathematical representation.

Hope that the following videos explain the concept better

## Air Pressure Again

A metal box, opened on the top, in put on the ground, then it’s closed welding a metal surface on it, in order to obtain a parallelepiped full of air. Suppose that the box walls are so strong that they would be perfectly resistant to the outside air pressure even if the box was empty. Then the air inside the box isn’t subjected to any influence by the external air pressure. In other words, standing inside the box there is no way to understand if outside there is air or empty space. Now, according to Stevin’s law, the pressure on the bottom surface inside the box should be equal to dgh, where h is the box height, much less than the air pressure outside! But actually the internal pressure is the same as the external pressure. I can’t find the mistake. Moreover i can’t understand how the pressure p in the gas law pV=nRT is involved in all that. thank you.

## 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??

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

• A guide into hydraulics – Part 1

## Want to learn fast? Be SMART!

In this busy world everyone wants to save time. Being students, learning is our primary job. To save time, we need to learn faster. But how?

The first step is to have a SMART goal!

S – Specific

M – Measurable

A –  Achievable

R – realistic

T – Time Bound

Having a Specific Measurable Achievable Realistic and Time Bound – SMART goal will increase your efficiency to grasp ideas faster.

While all of you may be having a long term goal, usually what you want to become after studies, you should have a short term goal, an objecting for every sitting of your studies too.

Have a Time Table – be specific what to study and when.

In the time slot for each, decide what and how much to study before you start. Know the outcome expected of you as a result of reading the portion. If it is not mentioned already, it is better to have a look at the questions based on the portion at hand before you actually read the topic.

Learn to read fast. Don’t go word by word while you read. Try to grasp a group of words at a go concentrating on the idea contained. Concentrate fully keeping in mind the objectives/ the questions you read based on the portion.

Do not reread or skip back until you have completed

Practice this daily and try to improve your reading and comprehension skills. This will certainly help you to score more as well as to live well in times to come.

## Problem from Work

Suresh pushes a create with a mass of 50KG down a slope with a rough surface, using a pushing force of 45N parallel to the slope downward. The slope is 2m in length. The inclination of the slope is 40 degrees. The crate starts at rest at the top of the plane. the frictional force between the plane and the crate is 140N. calculate the net force exerted on the crate.

## Dielectric slab problem

when a dielectric slab of thickness 6 cm is introduced between the plates of parallel plate condenser, it is found that the distance between the plates has to be increased by 4 cm to restore to capacity to original value . the dielectric constant of the slab is ?

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