Charge and its properties

1. Charge:    A property associated with matter responsible to produce electric and magnetic effects.
   

    Unit:    SI Ampers-sec or Coulomb    1 A.s=1C

            CGS    stat Coul or esu    or Franklin        1 Stat Coul=1 esu        1C=3´10⁹ esu

            Practical Unit    Amp.hr        1 A.hr=3600 C

            Faraday    1 faraday=96500 C

    Properties:

• Two kinds of charges – positive and negative. Similar charges repeal and opposite charges attract.
  
• Scalar:    Charge is scalar
  
• Additive
  
• Transferable:    Charge is transferable from one body to another.
  
• Quantized:    Charge is quantized. Smallest charge is a charge on an electron (-) and charge on a proton (+). It is known as fundamental charge and equals to 1.6´10^-19 C.
  
• Conserved:    Cannot be created or destroyed.
  
• Invariant:    It is invariant to frame of reference.
  

Effects:

• Stationary charge: Produces electric field known as electrostatic field.
  
• Charge in uniform motion:    Produces magnetic field in addition to electric field.
  
• Accelerated charge:    Produces electric as well as magnetic field and radiates energy in form of electromagnetic waves (EM Waves).
  

 

1. Materials:
   

   Conductors:
   

• Conduct electricity due to presence of free charge carries. In metals, which are conductors free charges carriers are electrons known as free electrons.
  
• Charge given to a conductor is always distributed on its surface. Its distribution on the surface (Surface charge density ) depends on the local radius of curvature. Smaller is the radius of curvature greater is the local surface charge density.
  
• A good conductor of heat is also a good conductor of electricity.
  
• In external electric field due to movement of free charges some charges appear on the surface. They are called induced charge and the phenomenon is called induction.
  
• Net electric field (resultant of the applied electric field and electric field of induced charges) is always zero inside a conductor.
  
• Amount of induced charge £ Amount of inducing charge.
  

Insulators:

• Cannot conduct electricity as no free charge carriers are present.
  
• In external electric field surface charges appear due to polarization. These surface charges are bound charge.
  
  • Net electric field (resultant of the applied electric field and electric field due to polarization) is always smaller than the applied electric field.
    
• Amount of surface charge due to polarization < Amount of charge inducing polarization.
  

 

1. Methods of charging a body:
   

   Charging by friction:    Electron transfer takes place when two different materials are rubbed on each other.
   

        Tribo-electric Series: (Enclosed in the end of class notes)

Charging By Conduction:    Transfer of charge from one conducting body to another by physical contact.

 

 

Charge distribution depends on the shape and size of both the bodies.

 

 

Wilma Rudolph, an Olympic Wonder

When Wilma Rudolph's mother was told by the doctors at the hospital that her daughter would never be able to walk again, she didn't believe it. It was this disbelief that enabled her child to walk years later. It was this same disbelief that allowed America to enthrone the first woman in history to win 3 Olympic Gold medals in a row.

As a baby, Wilma was born 4.5 pounds and 2 months premature on June 23, 1940 in St Bethlehem, Tennessee. But unlike most premature babies, she recuperated at home since her family could not afford the hospitalization fees. Probably due to her weak constitution and the insufficient medical care, Wilma suffered from a series of childhood diseases such as mumps, chickenpox, scarlet fever and then double pneumonia and remained pretty much bedridden. It was when her left leg started to be deformed that her mother finally took her to the doctors in Nashville.

There and then, Wilma Rudolph was diagnosed to be suffering from Polio. Refusing to believe that her 20th child (out of 22 kids) would never walk again, her mother took her to the hospital for bi-weekly physiotherapy sessions religiously. Every session was a painful experience but Wilma persisted on, believing in her mother when she said she would walk again.

Unveiling the Competitive Streak in Her

By the time she was 6, Wilma Rudolph was given metal braces to aid her in walking. Though the braces were supposed to help her, she hated them. To her, those were chains that imprisoned her at home and away from school. She yearned to break through them, run around the yard and go to school like any of the neighbourhood kids. She wanted to be free.

It was during this time, that she got literally frustrated at life's adversity and swore to herself that she would fight these diseases no matter what it might take. It was perhaps that same anguish that propelled her to rebel in a different way, revealing her competitive streak that would help her achieve the commendable success in her sport later on.

She started doing home physiotherapy with help from her siblings, and attending school a year later with the braces. A few years later, she awed everyone when she walked totally on her own, without any assistance into the church. She had won her first battle.

The Young Aspiring Sport Star

When she was in junior high school, she joined the basketball team. Despite her pleas to play in the games, Wilma remained a reserve for 3 full years where she watched, observed and analyzed the games. Until she was probably as good as her coach! In her 4th year with the team, she finally made an appeal to be in the starting lineup and when her wish was finally granted, she dazzled everyone by leading the team to an undefeated season and the state championships. Though they lost the championship title in the end, Wilma Rudolph earned the attention of the women's track coach, Ed Template at Tennessee State University and was invited to join the "Tigerbelles", a premier women's track & fields team in the region. At that time, she was only a high school student!

Joining the "Tigerbelles" gave her a different perspective. Running was no longer a gift that she took for granted like she used to when she won the tracks in school meets easily, as she lost every race in her first official track meet with the team. Her coach also made sure she worked hard. There was once when she was late for her training by half an hour and she had to run thirty laps as a punishment. One lap for every minute that she was late for. She also realized that she was being surpassed by athletes better trained than her. That kind of stimulated her competitive nature and sprung her into action, working with her coach closely to pick up breathing techniques and racing strategy, pace her starts which was her weakest area, and build up stamina and physical strength. At the same time, her mindset had also changed. No longer viewing her track seniors as heroes, she allowed herself to beat their timings.

Her efforts paid off as she turned out to be so good that the Tigerbelles invited her to join them in the 1956 heats for the national Olympics team. Not only did she make it into the team, she did well enough in the Melbourne Olympics to win a bronze in the 100-metres relay. At that time, she was only 16! When most of the girls her age were in high school mugging books and attending proms, she was already running for the Olympics! Although she did not win any of her own personal races, she vowed to be back in 1960, but not before being rewarded with a full scholarship by the Tennessee State to officially join the Tigerbelles as a result of her next 4 years' training efforts.

Shining Through Rome 1960

She made it to the Rome Olympics to compete in 3 separate events. Although she suffered from a sprained ankle then, she did not let it affect her performance and shocked the world by winning in an amazing fashion, breaking the World record (even though it was disputed later due to a claim of the strong tailwind) and the Olympic record in both the 100-metre & 200-metre races respectively. Even during their first heats of their 400-metres relay, Wilma Rudolph and her teammates had already broken the World record. A win was imminent for them in the finals, if not for a bad baton pass resulting in Germany and Russia taking the lead. However, her strong will to win propelled her to catch up and still win the race at only 0.3 seconds ahead of the second placed runner.

Wilma Rudolph's extraordinary achievements in Rome 1960 made her a darling of the European press who gave her the nickname "The Black Gazelle" and "The Black Pearl". Undisputedly, she also became the first woman in American history to win 3 gold medals in the Olympics and was crowned "the Fastest Woman in the World". Despite those, Wilma regarded her greatest tribute to be her homecoming parade in Tennesse. At that time, she proposed for the segregation laws for her homecoming events to be abolished and those were some of the first integrated events that the town has ever seen.

After that, Wilma Rudolph continued to be active in her sport mainly as a coach in high school track, sports commentator and mentor to famous African-American female athletes such as Jackie Joyner Kersee and Florence Griffith Joyner who became the next woman to win 3 gold medals. Both of them were remarkable women who were pretty much engaged in Wilma's spirit, even when she died of brain cancer at 54 on Nov 12, 1994.

What could we Learn From Wilma Rudolph?

Wilma Rudolph is a great reminder to us that we can overcome life's adversity with determination and sheer will power.

 

Understanding Tenses in English

Present Simple and continuous

Present simple:

1. We use present simple to talk about habits and routines.
   
   1. He starts working at nine o'clock.
      
   2. We see our friends every weekend.
      
   3. I often go running.
      
2. We use the present simple to talk about things that are permanent or always true.
   
   1. The moon goes around the earth.
      
   2. They live in Australia.
      
   3. Cats like fish
      
3. We use the present simple (not the present continuous ) with certain verbs, e.g. agree, believe, enjoy, hate, know, like, love, mean, prefer, remember, seem, think, understand, want, etc.
   
   1. I don't agree with you.
      
   2. Dogs don't like cats.
      
   3. They want to stay at home.
      

      
       

      Present continuous
      

      
       

1. We use the present continuous to talk about things that are happening now and things that are in the process of changing or developing.
   
   1. He is watching a film.
      
   2. They're having lunch.
      
   3. Digital cameras are getting cheaper.
      
2. We use the present continuous to talk about things that are temporary.
   
   1. Jack is working in the States till June.
      
   2. Jack's staying with Paula at the moment.
      

 

 

Test your Understanding.

Find the incorrect sentences.

1. Oh, no! It rains again!
   
2. Where do you live?
   
3. Are you speaking much English?
   
4. He doesn't usually listen to me.
   
5. I'm not wanting to go out tonight
   
6. John watches a film at the moment.
   
7. Paul comes from England.
   
8. I can't talk to you now. I drive the car.
   
9. I don't think you love me.
   
10. Cats are hating water.
    

    
     

    Answers
    

    
     

    1. Oh, no! It rains again! It is raining.
       
    2. correct
       
    3. Are you speaking much English? Do you speak
       
    4. correct
       
    5. I'm not wanting to go out tonight I don't want
       
    6. John watches a film at the moment. John is watching
       
    7. Correct
       
    8. I can't talk to you now. I drive the car. I'm driving
       
    9. Correct
       
    10. Cats are hating water. Cats hate
        

        
         

    
     

 

PHYSICS JOCKES

Q: What did the thermometer say to the graduated cylinder?
A: "You may have graduated but I've got many degrees"


A hydrogen atom came running into a police station asking for help....
Hydrogen atom: "Someone just stole my electron!"
Policeman: "Are you sure?"
Hydrogen atom: "Yes, I'm positive"
Policeman: "Oh, I thought you were just being negative again."



Q: Why is electricity so dangerous?
A: It doesn't conduct itself.

Q: What's the difference between a mathematician and a physicist?
A: A mathematician thinks that two points are enough to define a strait line while a physicist wants more data


SUBATOMIC PARTICLE STORE

The subatomic particle store had a sale last week.

Electrons: $0.10
Protons: A$0.10
Neutrons : free of charge


WHY THE SKY IS BLUE

I don't suppose you happen to know
Why the sky is blue? It's because the snow
Takes out the white. That leaves it clean
For the trees and grass to take out the green.
Then pears and bananas start to mellow,
And bit by bit they take out the yellow.
The sunsets, of course, take out the red
And pour it into the ocean bed
Or behind the mountains in the west.
You take all that out and the rest
Couldn't be anything else but blue.
Look for yourself. You can see it's true.


A neutron walks into a bar. "I'd like a beer" he says. The bartender promptly serves up a beer. "How much will that be?" asks the neutron. "For you?" replies the bartender, "no charge"


Why did the chicken cross the road?

Issac Newton1: Chickens at rest tend to stay at rest. Chickens in motion tend to cross the road.

Issac Newton2: It was pushed on the road.

Issac Newton3: It was pushed on the road by another chicken, which went away from the road.

Issac Newton4: It was attracted to a chicken on the other side of the road.

Gravitation can not be held responsible for people falling in love.


You enter the laboratory and see an experiment.
How will you know which class is it?
If it's green and wiggles, it's biology.
If it stinks, it's chemistry.
If it doesn't work, it's physics.

Q: Two cats are on a roof. Which slides off first?
A: The one with the smaller mew (Greek letter mu - μ).

Heisenberg is out for a drive when he's stopped by a traffic cop. The cop says, "Do you know how fast you were going?"
Heisenberg says, "No, but I know where I am."

Ivan Ivanovich, the great Russian scientist does an experiment. He wants to know how fast a thermometer falls down. He takes a thermometer and a light, a candle light. He drops both from the 3rd floor and recognizes that they are reaching the ground at the same time. Ivan Ivanovich, the great Russian scientist writes in his book: A thermometer falls with the speed of light.

When was Heisenberg born?
Oh, that's very uncertain.


Relativity:
Two hairs in my cup of milk is too much.
Two hairs on my head is too less.

How do Thunderstorms Work?

The Science of Thunder and Lightning

Scientists began to suspect that lightning must be a form of electricity as early as the 1700s because it looked similar to the sparks you could produce by rubbing certain materials together. Scottish scientist Robert Symmer had this off to a fine art and earned the dubious title of "the barefoot philosopher" because he was always removing his silk socks and rubbing them on things to produce sparks.
But it was a daring experiment by Benjamin Franklin in 1752, and one which he was lucky to survive, that proved it once and for all. Franklin flew a kite into a thundercloud and was rewarded with a stream of sparks flowing from the bottom of the kite string.

How is lightning generated?

Franklin's experiment worked because lightning is a multi-million volt electrical discharge between one cloud and another, or between a cloud and the Earth. It's produced when friction between tiny water and ice particles in clouds, called "hydrometeors", generates static electricity. For reasons that scientists don't fully understand, the smaller particles pick up a positive charge, and the larger particles pick up a negative charge. As these hydrometeors jostle about, updrafts push the smaller positively-charged particles towards the top of the cloud, leaving the negative charges concentrated at the bottom. It's possible that the solar wind, a million mile an hour maelstrom of cosmic radiation streaming out of the sun, may help in this sorting process.
Before long the cloud accumulates a massive potential difference measured in millions of volts. This electrical potential creates a powerful electric field, a bit like the contour lines on a map, which stretches from the bottom of the cloud to the ground (Earth). As a result the ground becomes positively charged as electrons are repelled away by the negative charge in the clouds. Tall and sharp objects, like buildings, trees, lightning conductors, and even golfing umbrellas, deform the contour lines of the field and push them close together, concentrating the electric field around the top of the object and making it a target for a strike. This happens when the field becomes sufficiently strong to overcome the insulting properties of the air, and the cloud discharges to Earth, producing a lightning bolt.
Each lightning flash is about 3 miles long but only about a centimetre wide. It discharges about 1-10 billion joules of energy and produces a current of some 30,000 - 50,000 amps, which heats the surrounding air to over 20,000 degrees Celsius, three times hotter than the surface of the sun (6000 degrees Celsius). In fact a single lightning bolt unleashes as much energy as blowing up a ton of TNT. And although it might look like a single flash, a strike is actually made up of between three and twelve individual lightning 'strokes', each lasting only a few thousandths of a second. This is what makes lightning appear to flicker.

And what about thunder ?

The intense heat of the lightning discharge superheats the surrounding air causing it to expand explosively. This creates a compression or 'shock' wave - the thunder - which spreads out through the air in all directions, travelling at about a fifth of a mile per second.
The flash and the thunder clap are produced simultaneously - as anyone unlucky enough to have ever got very close to a lightning strike can tell you - but the light from the flash travels much more rapidly (186,000 miles per second) than sound (0.2 miles per second approximately). The light therefore reaches you first, then a short while later (depending upon how far away the storm is), the thunder rolls in.

COLOUR OF SMOKE

When someone is smoking a cigarette, aside from the hacking and coughing, have you ever noticed that the smoke curling off the tip of the cigarette is blue, but when the smoke is exhaled it's white? The smoke changes color because the size of the smoke particles changes. The smoke particles rising from the cigarette tip are very small--smaller than the wavelengths of visible light. Because the particles are so tiny, when most light waves strike one of them they are not reflected back like a bouncing ball, but only slightly deflected from their paths. This is called "scattering." The various colors of light have different wave lengths, and the ones toward the blue end of the color spectrum are the shortest. So the short, blue waves are scattered about more by the tiny smoke particles because they are closer to the same size. Since mostly blue waves are scattered about the area, we see the smoke as blue. Most of the other, longer wavelengths go almost straight past the particles and we don't see most of them. Smoke particles that are sucked into the lungs are a bit bigger because they are not burned down completely. Many of them will remain in the lungs, hidden from the world until the biopsy. Many are exhaled, though, and when they come out they have changed again. While in the lungs, and on the way out, they pick up moisture so they become bigger still. The particles are now big enough to reflect all wavelengths of light equally. When all the wavelengths are reflected back they make white light, and so the smoke looks white.

ICE SPIKE.....

Why do ice cubes grow spikes?

The short explanation is this: as the ice freezes fast under supercooled conditions, the surface can get covered except for a small hole. Water expands when it freezes. As freezing continues, the expanding ice under the surface forces the remaining water up through the hole and it freezes around the edge forming a hollow spike. Eventually, the whole thing freezes and the spike is left.

A slightly longer explanation: the form of the ice crystals depends on the cooling rate and hence on the degree of supercooling. Large supercooling favors sheets which rapidly cover the surface, with some sheets hanging down into the water like curtains. These crystalites tend to join at 60 degrees and leave triangular holes in the surface. Hence, spikes often have a triangular base. The sides of the spike are sometimes a continuation of pre-existing subsurface crystalites, and can extend from the surface at steep angles.