## 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 ?

## 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.

## Single phase, two phase, three phase and multiphase electric generators – which one is more efficient?

I started referring to the above issue when one students asked, “Why do we use three phase generation of power and not two phase or four phase?”

Three-phase has properties that make it very desirable in electric power systems:

The phase currents tend to cancel out one another, summing to zero in the case of a linear balanced load. This makes it possible to reduce the size of the neutral conductor because it carries little to no current; all the phase conductors carry the same current and so can be the same size, for a balanced load.

Power transfer into a linear balanced load is constant, which helps to reduce generator and motor vibrations.

Three-phase systems can produce a rotating magnetic field with a specified direction and constant magnitude, which simplifies the design of electric motors.

Refer the following links for more …

http://en.wikipedia.org/wiki/Two-phase_electric_power

http://en.wikipedia.org/wiki/Polyphase_system

http://en.wikipedia.org/wiki/Three-phase_electric_power

## CBSE BOARD PAPER SOLUTIONS

CBSE Board Paper Solutions, this is one of the most popular search term among students today. The reason is evident.  CBSE Exams started.

Solving previous question papers is undoubtedly one of the easy way to get good marks with least effort, ie, without studying the entire book.

This idea is based on the fact that there are some bare esentials which cannot be avoided by any paper setter. These portions become evident by analysing the past question papers.

Rather than just trying to download the solved board papers, it would be better to identify the MUST STUDY PORTIONS with the help of an experienced teacher.

Please look for teachers who have experience in paper setting and evaluation with CBSE (or the respective Board)

They will be able to guide you on the way to write the answers better to score more marks.

## 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

## Solar Power

Suppose a PVC solar cell converts or absorbs 30% of the electromagnetic radiation which falls upon it, where I understand that “Gamma rays” or the such simply pass through it, would it not be so that a large portion of the 70% not converted, if directed to yet another PVC, could this second PVC convert 30% of the reflected 70% which the first PVC did not convert?

I believe the answer is “Yes, for the most part” which would than imply that the unabsorbed portion of the second pass could be directed again to a third PVC.

Is this correct?

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