Energetic consequences of doing things slowly

From charging capacitors to filling up water tanks.

Electrical engineers are familiar with the idea that when you try to charge a capacitor from a step voltage source, only half of the energy coming from the source gets into the capacitor while the other half is dissipated in the circuit resistances and/or lost as radiated electromagnetic energy. In other words, the efficiency is only 50%. Does it always have to happen that way? How can we do better?

The answer lies in shaping the applied voltage. If the rate of rise of the applied voltage is of the order of the time-constant of the circuit, the efficiency is much better than 50%. If it is very slow compared to the time-constant of the circuit, the efficiency approaches 100%. This is proved analytically as well as validated by circuit simulation in this article.

Even if we did not shape the voltage, if the capacitor doesn't have a linear relation between charge and voltage (in other words, it is a non-linear capacitor), the efficiency can still be very different from 50%.

The case of a step current source feeding an inductor is also analogous to the above scenario and gives similar results.

Taking a step back and applying this concept to any other domain (other than electrical engineering) can give some interesting insights. Pumping water into an overhead tank through a pipe having finite resistance (due to friction) is an example of an effort source feeding a potential energy storage element much like a voltage source charging a capacitor. Hence, it will take lesser energy if we were to pump the water slowly (trickle pumping) over several hours rather than doing it fast (gushing water) in fifteen minutes flat!

On a philosophical note, a very nice example is that of a teacher teaching a student. If the teacher goes far too fast beyond the grasping speed of the student, much of the knowledge doesn’t get transferred to the student’s brain.

Importance of stupidity in research

“If we knew what it was we were doing, it would not be called research, would it?” –Albert Einstein

Every time I manage to take a small step forward in my research, a plethora of new doubts and questions crop up. There are so many of these questions that I don’t seem to have an answer for – at least in the present. My collected PhD notes seem to be littered with more questions than answers. They expose my ignorance and probably prove my stupidity. 

That turns out to be quite a normal and happy disposition for a researcher. Martin Schwartz discusses about the importance of stupidity in scientific research in a heartening article for researchers. “The more comfortable we become with being stupid, the deeper we will wade into the unknown and the more likely we are to make big discoveries”, he writes.

Questions are the very things that drive the researcher and his/her research. You can’t seek answers if you don’t have questions. Does that make questions more important than answers? Possibly yes. The amazing human brain can come up with endless questions. Answers for questions that have been answered before come from prior art and learned men/women. For the unanswered questions, answers could come from various sources – deep thought by the brain itself, nature, experiment and, in some cases, a computer. 

Quite interestingly, Pablo Picasso once said "Computers are useless. They can only give you answers." They are after-all garbage-in, garbage-out machines. If the questions are meaningless, so shall be the answers. So if you've been thoughtful enough to pose the right question, it's acceptable to feel stupid about not knowing the answer so long as you're still seeking. In other words, feeling stupid is okay, being stupid is not.

Smart Car Race India 2010

Freescale Semiconductors and Centre for Electronics Design and Technology, Indian Institute of Science organized the 'Smart Car Race India 2010' from 27th to 29th September, 2010. Over 60 teams of engineering students from across the length and breadth of the country participated in the event. The prelims were held on the first two days. Thirty teams made to the finals that was held on 29th September. The top three teams were awarded attractive cash prizes.

The main objective of this national level competition is to foster the problem solving aptitude within the undergraduate and gradute student community. The challenge posed at the students was "to design and develop controller to steer a car on an unkown track". This is  implemented on toy cars equipped with on-board electronics. 

Freescale has been organizing this event in China, Korea, Malaysia and Mexico. This is the first time the event was held in India. From now on, this shall be a regular event in India too.

Related LInks:

http://www.livemint.com/2010/09/29222429/Selfdriving-cars.html
http://www.hindu.com/2010/09/29/stories/2010092957490200.htm
http://timesofindia.indiatimes.com/city/bangalore/Surat-engg-team-wins-smart-car-contest/articleshow/6654521.cms
http://pcsemicon.blogspot.com/2010/09/freescale-hosts-indias-first-smart-car.html
http://www.aaref.com/2010/09/30/news/surat-engg-team-wins-smart-car-contest/
http://www.efytimes.com/e1/51605/fullnews.htm
http://www.ciol.com/Developer/Developer/News-Reports/Freescale-names-winner-of-%E2%80%98Smart-Car-Race-India%E2%80%99/141789/0/
http://www.indiainfoline.com/Markets/News/Freescale-Semiconductor-hosts-Indias-first-SmartCar-Race-India-2010/4947952933
http://www.isaonline.org/index.php?option=com_content&view=article&id=1405:freescale-hosts-indias-first-smart-car-race-india--2010-for-engineering-students&catid=51:industry-specific-news-&Itemid=213
http://www.deccanherald.com/content/100941/no-f1-had-edge-seat.html
http://www.newkerala.com/news/world/fullnews-52776.html

  
Edit on 17 Dec 2010: Video added

 

The Art of Teaching

Much of our competence, and for that matter even the interest we have, in a subject is down to how well we were taught that subject. A good teacher has a profound influence on the capabilities and performance of his pupils in life. Science and engineering education is no exception. With my sights set on taking up teaching and research as a career, I'm always impressed when I come across someone who is exceptional and creative in his pedagogical methods. 

Recently, thanks to YouTube, I stumbled upon a few lectures from one such gifted teacher, Professor Walter Lewin, who teaches Physics at MIT. His methods are truly worth emulating as the following video would testify.

With several universities across the world opening up their lecture halls to the world, by providing free access to recorded lectures, the enthusiastic student of today has an invaluable resource to tap from.

Here are a few such links from generous universities:

• MIT Open Course Ware - http://ocw.mit.edu/index.htm
• UCB Webcast - http://webcast.berkeley.edu/courses.php
• NPTEL (A Joint Venture by IITs and IISc) - http://nptel.iitm.ac.in/
• Academic Earth - http://academicearth.org/   
• Free Lecture Videos - http://www.freelecturevideos.com/
• 101 Killer Open Courseware Projects from Around the World - http://bestcollegerankings.org/2009/101-killer-open-courseware-projects-from-around-the-world-ivy-league-and-beyond/

Lightning - An Overview

[Download pdf file of this article here]

Lightning has always evoked fascination. Recently I spent some time contemplating and perusing through lots of resources on the internet and in print about lightning and the possibility of harnessing energy from it. Here's a brief overview of what I gleaned from various sources.

The important figures associated with lightning (typical values):

1. Voltage between cloud and ground ≈ 10^8 to 10^9 V (upto a billion volts)
2. Current during lightning discharge ≈ 10 to 200 kA (hundreds of kilo-amperes)
3. Peak power involved ≈ 10^10 to 10^12 W (several giga-watts)
4. Energy discharged ≈ 250 kWh (hundreds of units)
5. Temperature ≈ 30,000 ºC (about five times the surface temperature of the sun!)
6. Duration of discharge ≈ 0.2 s

A collection of interesting facts about lighting:

1. On an average, the earth receives 3 million lighting flashes a day i.e. about 40 flashes every second.
2. Tropical Africa is the most struck by lightning, with up to 295 days a year subject to electrical storms. Lightning strikes most frequently in the Democratic Republic of the Congo (formerly Zaire)
3. 90% of all lightning strikes are cloud-to-cloud.
4. Thunder produced by a lightning strike travels one mile (1.6 km) every five seconds. Thus, counting the number of seconds between the visible "flash" and the audible "bang" and dividing by 5, provides the distance in miles at which the strike has occurred.

Types of lighting: 

    1. Cloud-to-ground

        - Negative lightning
        - Positive lightning (bolt from the blue!)
    2. Cloud-to-cloud or inter-cloud
    3. Intra-cloud
    4. Cloud-to-air

How it happens:

Certain types of clouds - known as cumulonimbus clouds or thunderclouds - develop a strong charge separation with large negative charges at the bottom and large positive charges at the top possibly due to the friction (tribo-electric effect) between upward rising air and falling water droplets and ice.  A large “shadow” region of positive charge is created under the cloud due to electrostatic induction. When the electric field between the bottom of the cloud and the surface of the earth becomes strong enough, streaks of ionized air (negatively charged stepped leaders) reach out downwards from the clouds while positive streamers grow upwards from objects on the earth. When the two meet, a short circuit is created for humongous amounts of charge to be transferred from the cloud to the earth within a fraction of a second and that is what we see as lightning. The huge current through the conducting channel creates large amount of heat, light,  sound and radio waves.

Keywords: cumulonimbus clouds, thunderclouds, triboelectric effect, electrostatic induction, negative stepped leaders, positive streamers, return stroke, dart leaders, secondary strokes

Lightning Effects:

• Lightning contributes to nitrogen fixation.
• If the lighting current path passes through rock, soil or metal these materials can become permanently magnetized due the fleeting but very strong magnetic field induced by the large current. This effect is called Lightning Induced Remanent Magnetism (LIRM).
• The heat of lightning which strikes loose soil or sandy regions of the ground may fuse the soil or sand into glass channels called fulgurites.
• Trees are common lighting targets. Of all common trees, the most frequently struck is the oak.
• The electrical discharge during lightning rapidly superheats the discharge channel causing the air to expand rapidly and produce shock waves heard as thunder. The rolling and gradually dissipating rumble of thunder is caused by the time delay of sound coming from different portions of a long stroke.

Lighting Safety:

• Lighting can even reach you indoors of you are in contact with the telephone (landline) or plumbing – basically anything that has a continuous conducting path extending to a place outdoors where the lighting can strike.
• Water is an excellent conductor, so it’s wise to stay away from lakes, ponds and pools during a lightning storm.
• Even if the bolt strikes an object near you, the ground current that flows from the point of strike in all directions can easily flow through a person standing with his feet part. So during a thunder storm it’s advisable to (1) stay low, in a crouched position (to reduce the probability of the bolt striking you) especially if you are in a flat region with no taller structures than yourself  (2) Keep your feet together and have as little of your body touching the ground as possible (to reduce the ground current flowing through you)
• Rubber tires aren’t why you are safe in a car during a lightning storm. In strong electric fields, rubber tires actually become more conductive than insulating. You are safe in a car because the lightning will travel around the surface of the vehicle and then go to ground. This occurs because the vehicle acts like a Faraday cage.
• Lighting arrestors and lightning rods
• Static discharge wicks in airplanes

Problems with harnessing energy from lightning:

1. The discharge of extremely large power concentrated within a very small span of time would require a very very huge and costly device to tap the energy.
2. Even if the device is somehow built, lightning itself is highly infrequent, inconsistent and unpredictable. We never know the exact time and place where it will strike.
3. Even if you manage to find a place that receives lighting consistently, a lighting strike dissipates so much energy in heat, light, sound and radio waves that there is not enough left to be worth collecting.

Possible ways to overcome these problems:

• Do not let the lighting discharge happen as a sudden flash. Find a way to slowly drain the stored charge in the cloud-to-ground capacitance and store it somewhere for being tapped later on.
• As most of the lightning strikes are cloud-to-cloud and also because much of the energy in cloud-to-ground discharges are dissipated in the intervening medium as heat, light, sound and radio waves, the only way to harness energy from lightning is to go to the clouds and do something up there. To put it in Dr. Martin A. Uman’s words, “trying to harvest the energy of lightning from the ground is hopeless”.

References and useful links for information on lighting:

1. Lightning Primer from NASA http://thunder.msfc.nasa.gov/primer/index.html
2. NASA answers on lightning energy harvesting http://www.nasa.gov/centers/kennedy/about/information/science_faq.html#1
3. Wikipedia article on lighting http://en.wikipedia.org/wiki/Lightning
4. Good lighting explanation and videos http://science.howstuffworks.com/lightning.htm
5. Can lightning be tamed? http://www.planete-energies.com/content/sky.html
6. Harnessing lightning power http://www.weatherimagery.com/blog/harnessing-lightning-power/
7. Harnessing lightning power http://www.science.edu.sg/ssc/detailed.jsp?artid=5001&type=6&root=5&parent=5&cat=57
8. Harnessing lightning power http://peswiki.com/index.php/Directory:Lightning_Power
9. Discussion forum http://answers.google.com/answers/threadview/id/765667.html
10. Lightning Farms http://www.nytimes.com/2007/12/09/magazine/09lightningfarm.html?_r=3
11. A detailed article on lightning http://www.electricalfun.com/lightning.htm
12. Nikola Tesla: Power from Lightning http://www.mikebrownsolutions.com/tesla-lightning.htm
13. “Lightning”- A book by Dr. Martin A. Uman, a leading authority on lightning.

Sleep Detector Power Saver

I remember umpteen instances when I've seen people leave their lights and/or televisions turned on and fall asleep. While the person is recharging himself his appliances are continuously hogging power all night for no useful purpose at all. Of course the easiest solution to the problem is for people to realize the mistake and be responsible enough to turn off all unwanted utilities when they go to sleep.

But since we still have so many careless people around, there is a potentially huge market for a product that could detect sleep in a person and take action accordingly - switch off lights, TV etc. Sleep detection could be done based on monitoring of one or more of various parameters - heart rate or pulse rate, body movement, body temperature, respiration rate etc. The major challenge in such a product would probably be to identify which among these myriad options would provide the cheapest and the most reliable way to detect sleep. Any answers?

[This post is an elaboration of Problem-3 on the post "Nine Problems Worth Solving"]

Jerky Ride Writing Assistant

Travelling by bus, train or car can be tedious if the journey is long and more so if you are all alone. Many resort to reading in order to pass time. There are times when I felt like writing something when traveling. But because of the jerky nature of the ride, it becomes rather difficult to write anything legibly. It's at times like these that I've often wondered if there could be some device that could be strapped on to my wrist, which would allow me to write normally the way I would in a stationary and jerk-free scenario. It could probably compensate for the jerks by applying precise forces (of the right magnitude and direction) on the hand - some sort of an active noise cancellation!

Another possible solution to the problem is to have some sort of a damper or a shock-absorber structure that keeps my hand and the notebook steady irrespective of vibrations in the vehicle. Any thoughts and/or suggestions from the reader are most welcome.

[This post is an elaboration of Problem-2 on the post "Nine Problems Worth Solving"]