Friday, August 31, 2012

Working of a capacitor

Capacitor and Battery Analogy

Capacitors are analogous to Batteries because they both are used to store and charge electrical energy, though they both work differently.

Batteries have two terminals one positive and one negative. And they involve chemical reactions to produce electrons at one terminal and absorb at the other. While capacitors are not able to produce charge or electrons, but only stores them. Capacitors are much simpler in comparison to batteries.

The terminals in the capacitors are connected to two metallic plates separated by an insulator (materials which do not conduct electricity) or dielectrics. A capacitor can be easily built at home using metallic foils and air or piece of paper as dielectric. The capacitor thus formed will have a very low tendency to store charge.

Also, the major difference between battery and capacitors can be that Capacitors can easily dump their charges in a fraction of seconds while batteries may take minutes to discharge.


The dielectrics used in the capacitors can be any insulator which polarizes on the application of electricity. However Mica, porcelain, Teflon, Cellulose, Ceramic, Glass and even Air are used in practical capacitors which are best suited for the functions of the capacitor.  The size and the type of dielectric used determine the application for which a capacitor may be used.

Capacitors which have air as a dielectric are used in tuning circuits in the radio and other devices, while capacitors with ceramic dielectrics are used for high frequency purposes such as in Antennas.  For high voltage capacitors glass dielectrics are used. Capacitors are manufactured to serve many purposes like a small plastic capacitor used in the Calculators to Ceramic Capacitors used in Supercomputers.

What happens on connecting a capacitor to a circuit? :

The figure shows the circuit symbol of a capacitor.

When we connect a capacitor to a battery, the plate connected to the positive terminal of a battery loses electrons to the battery and the plate attached to the negative terminal absorbs the electrons that the battery produces. Once the capacitor is charged fully the voltage across the capacitor becomes equal to that of the battery.  Small capacitors hold small amount of charge but large capacitors have the ability to store charge in large amounts.

We can also observe a working capacitor in nature, in the form of lightning, the cloud and the ground being the two plates of capacitor and lightning is the releasing of charge between the two plates. It is obvious that when the capacitor is that large, huge amount of charge can be stores in it.

Let’s now take up a capacitor connected in series with a bulb and a battery as shown in the figure.  If the capacitor used here can store large amount of charge or we can say if we are using large capacitor we can notice that

  • The bulb will light up as current flows through it to charge up the capacitor , But we can observe the bulb going dim as the capacitor gets charged to its capacity and when the capacity is reached the bulb goes off .

  • Now if the battery is replaced by a wire, the current starts flowing from its one plate to the other and the bulb will light up initially and then go dim as the capacitor starts discharging. The bulb goes off again when the capacitor is totally discharged.

The Capacity of a capacitor to store charge or capacitance of a capacitor is measured in terms of Farad. 1-Farad is the capacitance of a capacitor which can store 1 coulomb of charge at 1 volt.  A one farad capacitor can be very large it can be as big as a 1 liter soda bottle, this being the reason why capacitance is usually measured in microfarads and general usage of small capacitors.

Applications of Capacitors:

  • Capacitors are used for high frequency and speed applications such as in lasers to get highly bright and instantaneous flashes.

  • In tuning circuits along with inductors to match a frequency.

  • As noise filters and to block DC components of the current.

  • In flash lights of a camera.

  • For signal processing.

Safety and Hazards
Capacitors can retain charge for a longer period after being disconnected from a circuit, this charge can be fatal  and is very dangerous this is the reason why Televisions have a "Do Not Open" warning over them as they use large capacitors for tuning purposes and these capacitors store large amount of charge which can even kill .

Wednesday, August 29, 2012

Fiber optic communication

Fiber optic communication refers to the method of sending information from one

place to another, with the help of pulses or a beam of light with the help of optical fibers. The light forms the electromagnetic carrier wave which carries the information. This concept of communicating has revolutionized the communication industry. Optical communication being more advantageous over the electrical transmission has replaced the copper wire communications with optical fibers largely.

The following steps are involved to communicate using an optical fiber:

    • Creating an optical signal and using transmitter to send the signal across the optical fiber.

    • Make certain that the information in the signal is not lost and the signal is not weak or distorted.

    • Receiving the optical signal by the receiver

    • Conversion of optical signal to electrical signal as instruments and electronic appliances work upon electrical signals only.


Total Internal Reflection – Principle behind Optical Fiber

Today telephone signals, internet communication and digital television signals are transmitted using optical fiber cables. Optical fibers work on the principle of Total internal reflection.  Total internal reflection says that when the light strikes the boundary of the optical fiber at an angle greater than the critical angle, the light is totally reflected.  Critical angle refers to the angle at which the light is totally reflected and no refraction takes place. Light which enters the fiber at angle greater than the critical angle is only able to propagate through the optical fiber. The light strikes the boundaries of the cable and bounces back and forth and reaches the destination.

Construction of the Optical Fibers

Optical fibers are made up of two concentric cylindrical glasses. The inner core is surrounded by a concentric core made up of glass and of lower refractive index known as cladding. Protective layer with which the cladding is surrounded is called as protective sheath. The total internal reflection takes place at the cladding – core interface. The core diameter ranges in a few microns and is not much larger than the wavelength of light used.  When high data transmission rates are not required, core with comparatively large diameters are used which may be of a few hundred microns.





English: Optical cable Nederlands: glasvezel k...



      1. Cheap: As it is mainly made up of glass which is manufactured from sand, there is a huge supply of sand available in the world in comparison to copper or aluminum. Hence they are cheap.

      2. Safety: The medium of transportation of data is light and hence it is safer as electricity is not used and there is no chance for sparking to occur.

      3. Security: Criminal intrusions and routing of the information to unwanted receivers can be reduced as electrical signals are not used.

      4. Small size and light weight and hence the optical fibers can be used easily.

      5. Temperature: Melting point of glass is much higher than copper and thus they do not melt easily.

      6. Deterioration: Glass is immune to corrosive substances and can withstand even the harsh environment.   Moisture, Acids and toxic vapors do not harm optical fibers.

      7. Long Life: Optical fibers usually live long for about more than 100 years.



      1. Limited Application: Can only be used on ground, cannot leave the ground or be associated with the mobile communication.

      2. Nuclear Radiations: on exposure to the nuclear radiations the glass darken and the harder the glass is easily it’ll lose its color.

      3. Low Power: Light emitting sources are limited to low power and tough high power emitters are available but are costly.

      4. Fragility : The optical fibers can be broken easily due to age or vibrations

      5. Distance: The distance between the transmitter and receiver must be short or if it is long signal repeaters are used to ensure the signals are not weak.



      • In the telecommunication industry to transmit and receive telephone, internet and television signals.

      • It is used in various surgeries and operations and to illuminate the parts of the human body which are generally inaccessible. It is also used as lasers for surgeries.

      • Used in hydrophones for seismic and sonar uses, as wiring in aircrafts and in submarines.

      • For imaging and lighting in hard to reach areas.

Friday, August 10, 2012

Download CBSE Physics Question Paper 2012

CBSE Physics Question Paper 2012 SET 1

CBSE Physics Question Paper 2012 SET 2

CBSE Physics Question Paper 2012 SET 3

What you do today could affect what happened yesterday!!

Can the future affect the past?

What you do today could affect what happened yesterday – that is the bizarre conclusion of a thought experiment in quantum physics described in a preprint article by Yakir Aharonov of Tel-Aviv University in Israel and colleagues.


What do you think? Post your comments after reading the articles.

What is Higgs Boson?

Why do we need Higg's Boson? Helen Heath explains why the Standard Model needs the Higgs boson.

Gordon Fraser and Michael Riordan argue that the boson discovered at CERN should be known not as the Higgs boson, but the "higgson"

Tuesday, August 7, 2012

A nationwide competition for aspiring entrepreneurs

The Indian School of Business and The Indus Entrepreneurs (TiE-ISB Connect) have
Indian School Of Business - Hyderabad

launched a nationwide competition named Biz Quest for start-ups. To be held from September 20 to 22 at the ISB Hyderabad campus, this initiative will also support aspiring entrepreneurs, early stage and growth stage entrepreneurs to showcase their business potential among venture capitalists and angel investors.

The winner of the competition has a chance to grab up to Rs 1 crore.

Why does a moving train drag us when near?

When we are near the moving train,we feel that the train drags us,,,  at the same time when we are near the window side in the moving train,y the plants or trees which is near the railway track get outward movement or repel from us? plz explain which concept behind this act?

GM43 diesel train - moving barley, Clare valle...

Asks Babu.

The dragging experience is explained using Bernoulli's equation.

As the train is moving fast, it creates a low pressure area. So, the surrounding objects get dragged from high pressure to low pressure  area

We are about to cross 1 million hits!

Yes!  is about to cross 1 million hits (since 1 march 2011)

Share the joy

Monday, August 6, 2012

Curiosity Rover Landed on Mars

The mars exploration begins!

NASA's curiosity rover landed safely on mars. The 2,000 lb. NASA Curiosity Rover landed on Mars at 1:39am, early Monday morning EST.

Watch the video showing the landing of Curiosity Rover on Mars

Read More

Almost immediately upon landing early Monday, the Curiosity craft transmitted to Earth a series of photographs showing its own wheels safely on the surface of Gale Crater near the equator of Mars.

"There is the wheel of the rover safely on the surface of Mars," said one exuberant flight engineer from NASA's Jet Propulsion Laboratory in Pasadena, Calif., which is managing the $2.5 billion mission.

Almost immediately upon landing early Monday, the Curiosity craft transmitted to Earth a series of photographs showing its own wheels safely on the surface of Gale Crater near the equator of Mars.

"There is the wheel of the rover safely on the surface of Mars," said one exuberant flight engineer from NASA's Jet Propulsion Laboratory in Pasadena, Calif., which is managing the $2.5 billion mission.


The Physics of Running explained - PhysicsWorld Video

The Physics World explains the Physics of running through this simple narrative video.

Friday, August 3, 2012

Ensurance of Performance in Physics - Physics Help

Ensurance of performance is what many a students need while joining any programme. At PhysicsFans, we would like to start a section dedicated to ensurance of performance of students is exam.

Bahasa Indonesia: SMA Trinitas, Ulangan Umum

The section will provide

  • Tips to perform well in exam

  • Guidelines on how to study, how to write exam well etc.

  • Questions bank arranged chapter-wise/ topic-wise

  • Collection of question papers from various boards

  • Topic wise arranged lecture notes, video lectures

  • ... and more

What else do you need?

Please post your suggestions as reply to this post.

You can also contribute towards the development of this section by creating blogs and forum posts with the tag "ensurance"

Post your blogs on Science related topics here

Hi Physics Fans!

We have enabled blogging by every member. Have an idea? You're welcome to post'em here!

The posts will be published after scrutiny by admins. We prefer Science related articles, preferably Physics.

You can write on:

  • Latest news, events and happenings in the scientific world.

  • Promotional blogs on websites, institutions or persons

  • Create forums, Forum Topics and replies

  • ... and anything else if it is related to the promotion of Physics!

Wednesday, August 1, 2012

Indian Theoretical physicist Ashoke Sen wins world's richest academic prize

Ashoke Sen, a string theorist at Allahabad's Harish Chandra Research Institute, became a millionaire overnight as he is one of the nine winners of the first Yuri Milner Fundamental Physics Prize which at Rs 16.7 crore is the most lucrative academic prize in the world.

The prize, which is nearly three times that of the Nobel purse - which is frequently shared by two or three winners - has been instituted by Yuri Milner, a Russian student of physics who dropped out of graduate school in 1989 and later made billions as an investor in companies like Facebook.


CBSE Published Question Paper and Answer Key of Proficielncy test 2012

Download Question Paper and Answer Key of Proficielncy test 2012 published by CBSE

Mathematics (Set-A)
Mathematics (Set-B)
Mathematics (Set-C)
Mathematics (Set-D)
Science (Set-A)
Science (Set-B)
Science (Set-C)
Science (Set-D)
Answer Key - Mathematics
Answer Key - Science

IIT Kanpur to adopt new JEE for 2013

IIT Kanpur had been the first to oppose the new format of the Common Entrance Test (CET). However, it has decided to soften its approach for the sake of IIT aspirants preparing to appear for the exam next year. To remove the uncertainties as soon as possible, it has decided to adopt the new Joint Entrance Exam (JEE) for the year 2013 as an interim measure.

IIT Bombay votes against new JEE

IIT Bombay votes against new JEE

In a poll conducted by the IIT-B Alumni Association (IITBAA), it has been found that 78% of the 1,800 respondents voted against the new two-tier Joint Entrance Exam (JEE). The respondents included 49% faculty members, 70% alumni and 85% students of IIT Bombay. The online poll was started before the compromise formula was reached but was kept open for a week after the new JEE formula was announced.