AUTOMATIC STREET LIGHTS:-

In our daily life we see glowing of street lights even though there is sufficient light outside.There is a lot of wastage of energy occurring due to this.

Thus to avoid this energy wastage ,the circuit shown below can reduce this and save lot of energy in this circuit we use the light sensor names LDR (LIGHT DEPENDANT RESISTANCE) as shown below to detect the presence of light .

now first we learn about,

How an LDR (Light Dependent Resistor) Works ?

An LDR is a component whose value of resistance ,changes with the light intensity that falls upon it. This allows them to be used in light sensing circuits.

A typical LDR looks like as shown below,

The symbol for LDR looks like as shown in the below picture

when there is abundance of light there is a low resistance in the the LDR because all the electrons gain energy from incident light (photons)go to conduction band and participate in the conduction,

but in the absence of light there is no sufficient energy for the electrons to go to the conduction band so there is no available free electrons for conduction,so it acts as high resistance .The curve showing the variation of resistance in shown in the figure  below  

CIRCUIT DIAGRAM

FOR USING LDR IN AUTOMATIC STREET LIGHT SYSTEM

In the above circuit we use the help of transistor, the LDR is connected between the Base and emitter,consider the case when there is light .

since there is light there is low resistance of LDR so there is less voltage drop across LDR.This voltage drop across LDR is equal to voltage across "Vbe",this "Vbe" cannot drive the transistor into ON condition.So there wont be any collector current,So LED  dosen't glow.

While in another case , when there is no light the LDR  becomes very high resistive and there will be a high voltage drop across the LDR, this implies high drop across the  "Vbe".So the transistor turns ON and there will be collector current by which "LED GLOWS"

This  is how we made use of light sensor and transistor for our convenience.

In practical application the street light can be used in the place of LED

Other Applications of LDRs:-

Camera shutter control

LDRs can be used to control the shutter speed on a camera. The LDR would be used to measure the light intensity which then adjusts the camera shutter speed to the appropriate level.

why AC(alternating current) cant be stored ,like DC in batteries ?

The AC(alternating current) is the current or voltage whose magnitude (generally 230V in India and 100V in US) varies with time with some frequency (generally 50Hzs in India and 60Hzs in US) , but in the case of DC the magnitude of the is constant with time (like a step function).so DC has no frequency. 

       
                          

                                       DC-Voltage

we can see from the above pictures that the AC varies with time but DC is constant, moreover the DC voltage has a average value, but the average value of the AC voltage is zero for full cycle.The capacitor can store only DC voltage because average value is equal to the dc voltage,but in the case of the AC voltage,we  cant store because it average value is equal to zero.

      Here we are considering the case of capacitor only because all the practical batteries are nothing but capacitors which can with stand based on their voltage ranges. 

# So for this reason we are interested in storing in DC voltages only

THE STORY BEHIND 15TH SEPTEMBER

THE STORY BEHIND 15TH SEPTEMBER

 ---NUTAN SATYA SAI RAJ .K   
  Every story has a hero.The hero of our story is Sir Mokshagundam Visveswaraya!!!                                                         

                                                 

        Sir Mokshagundam Visvesvaraya is an Eminent Civil Engineer and Excellent Statesman. He is the oldest surviving icon from 20th Century. He was born in a poor brahmin family in Muddenahalli in 1860.He was an engineer with a flair for bold and creative ideas. His studies and research concentrated mainly on flow of water and building dams. He has the credit of inventing ‘Automatic Flood Gates System’ and ‘Block Irrigation System’ which are still considered to be marvels in engineering and they were considered as best design in Asia in 1903.

          Once Mokshagundam Visvesvaraya, as Chief Engineer for Karnataka state visited beautiful Sivasamudra Waterfalls, located in Karnataka over the bank of river Kaveri. After watching them, he made a comment immediately, "What a huge waste of Energy?”. Every one present over there was shocked by the statement. In a flash, he got an idea to build a Hydro-electricity Project over there. His eyes didn't see the beauty of the water falls but only saw the loss of Energy. Hence, we can understand the dedication levels of an ideal engineer present in him!

           

           He also holds the credit of planning the ghat-road from Tirupati to Tirumala. The greatest thing about that is, there was no single rock fall and accidents occurred till today on that road. But surprisingly, some rock fall and accidents occurred on the other road which was constructed by new generation engineers. Visveswaraya sir planned the road in such a way that he observed each and every corner of the mountain for few months and designed efficiently with utmost care. Thus we can see a high level quality engineer present in him!

Have you ever heard about floods in Hyderabad?  Surely the answer is NO. It is all because our greatest engineer Visveswaraya Sir. In 1908 there were severe floods to Musi river in Hyderabad. Almost 50,500 people died and many became homeless. Then he developed flood protection system by designing and constructing the dam and drainage systems in Hyderabad. With his engineering skills, he turned Hyderabad to flood-free city. He also saved the Visakhapatnam port from sea erosion. The part of the port which was constructed by him was very less affected even from the recent Hudhud cyclone. This shows his expertise!

He built Krishna Raja Sagar Dam which is the largest Dam in Asia at the time of its construction. It is considered as one of the greatest achievements. At the age of 90, Visveswaraya sir constructed a bridge over river Ganga in Bihar. Thus we can understand level of interest present in him. He said that “Engineer is a person who creates things which are not created by God”. These are a few of his great works done by him. He is an engineer with a great passion! "Work is Worship" is the motto of Sir Visveswaraya!

The Indian government considering his greatness honoured him with Bharat Ratna in the year 1955 and didn't find an engineer like him and therefore celebrates his birthday 15th September as National Engineers Day every year. There are 1.3 billion Indians, 1.5 million are engineers. And yet, most of us are unaware of the only day dedicated to this pioneering community of our country. This article focuses a great Indian engineer Sir Mokshagundam Visveswaraya. It is the minimum responsibility of every engineer to know about the greatness of him and adopt the qualities of him.I consider my standards are not sufficient to describe the greatness of Visveswaraya Sir, but I am still fortunate in trying my level best in writing this article and I wish a very Happy Engineer’s Day in advance to all our budding and expert innovators reforming our Nation.

" Remember your work may be only to sweep railway crossing but it is your duty to keep it so clean that no other crossing in the world is as clean as yours."   --- Sir Mokshadundam Visveswaraya.

                             A video on visveswaraya sir in social media                                                                 

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