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Physics: Fields

Concept map on magnetic, gravitational and electrical fields and their applications in society, environment & technology
by

Jennifer Shi

on 12 April 2011

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Transcript of Physics: Fields

fills all space Fields fundemental are different particles = gravitational fields

Gravity is the force of attraction between all objects with mass weakest force Attraction Only any distance mass it is too small to be noticed between certain objects 9.80 N/Kg gravitational Fields exist in the space surrounding an object in which the force of gravity is exerted on objects vectors force vectors law of Universal gravitation applies to all bodies in the solar system where F G is the magnitude of the force of gravity G is the universal constant m 1 is the mass of the body being influenced m 2 is the mass of the body whose gravitational field is influencing r is the distance between the centers of the bodies Gravitational Fields is created by every object force is inversely proportional to distance squared force is proportional to mass F r 2 M F Earth's Gravitational Fields variations of gravitation of field are due to different densities within the Earth Core, ,mountains, ocean trenches Example 1: Solution: G = 6.67 X 10 N m / kg -11 2 2 . F G A 456kg satellite is approximately 2.5 X 10 m away from Earth's
center. What is the magnitude of the total gravitational field strength excerted
by the earth. = ? m 1 = 457kg m 2 = 5.98 X 10 kg 7 24 r = 2.5 x 10 m 7 F G = G X m X m
r 1 2 2 __________ G = 6.67 x 10 N m / kg -11 = 2 2 (6.67 X 10 N m / kg )(457kg)(5.98 X 10 kg)
(2.5 x 10 m) -11 2 2 7 _____________________ = 7 291 270 480 = 7. 3 X 10 N ( towards the earth's centre) 9 Newton by in 1687 principia universal gravitational constant by Henry Cavendish in 1798 Implications Tide on Earth Earth's tides are a result of the gravital pull of the Sun and Moon. Tides are caused by the gradiant; the amount of gravitational field change from Earth's
near side to its far side there is a larger field when facing the sun the gravitational field is not unifrom across the earth water bulges towards the sun in near side and away in far side Despite the sun's greater gravitatonal field, lunar tide exceeds solar tide the moon is closer, thus there is a larger gradiant between the near and far sides Tidal Energy Tidal power is a form of hydropower that converts tides into electricity it uses the rise and fall of the tides which are caused by gravitational fields Tidal energy is a renewable and clearn source of energy elimitates green house gases (from burning fossil fuels) that contribute to climate change Economic Considerations the technology for tidal energy is quite developed main concern is high construction cost and time high capital cost and 10 year construction rate sustainability again gives it an edge over fossil fuels which are on the brink of exhaustion operational in only certain regions of the world as it is limited by geography. however it will generate jobs and stimulate the economy But as fossil fuels deminish and become more expensive, those able might turn to tidal energy does have low maintaince costs Equipument may effect ecosystems in the area Society with fossil fuels deminishing and the world population increasing, it is becoming harder to keep up with energy needs. tidal energy provides one of the alternative forms of energy; will help in meeting the world's energy demand when fossil fuels are gone. Has no air pollution; cleaner air = less health concerns Satellites in Space A understanding of gravitational fields . . . allowed for satellites in space . . . . Satellites are objects that are placed into orbit by human endavour . . . manmade 1st is soviet's Sputnik 1957 in fixed mobile A need for gravitational fields . . . it is not enough to just calculate the speed needed for the satellite to escape Earth's gravity then it will fly off into space instead, there needs to be a balance between gravity's pull on the satellite and the inertia of satellite's motion. calculations like ones using the law of universal gravitation help determine the strength of earth's gravitational field (pull of a gravity) at a certain distance away and in turn determine the speed of the satellite need to launch it into orbit at that distance. in fact, the satellite need to reamin within Earth's gravitational fields the law of universal gravitation allow scientists to calculate the magnitute of the earth's gravity on an object at a certain distance away. Known the magnitude of the field at this point will then allow scientists to know eactly how much energy and speed is need to place the in orbit there. Weather satellites can monitor the weather for more current and accurate reports used for storm watch: large storms such as hurricanes can be monitored after and before formation people can be informed to evacuate or move to a shelter much earlier ( be more prepared ) resulting in less injury, mortality and damage Military Purposes stallites were first imployed by the military as top secret devices for navigation and espionage they still are today, helping to guild earth bound weaponary, provide terrain information (imaging) or spying on other countries. In fact, another arms race might begin for the domination of space this time. As in space weaponary are being developed along with anti-satellite weaponary in leading world powers like America and China. Communications use to transmite t.v and telephone signals, even cable t.v rely on satellites newspapers and magazines are more timely because they transmit their text and images to multiple printing sites via satellite to speed local distribution. Emergency radio beacons from downed aircraft and distressed ships may reach search-and-rescue teams when satellites relay the signal GPS sytems are helpfull in people's everyday lives as well as allowing goods to reach distributors more savely and efficently as shipping vehicals can be tracked by companies. Scientific Reearch satellites like the international space station, the Hubal telescope all contribute to scientific research and discovery allowing scientists to search for other life forms in space, discover the mysteries of the universe, look at distant planets and stars understanding of the formation of the universe, galaxies, stars, planets and earth Electric Fields any charged object can create charged particles e Electricity law of electric charges opposites attract similiar repel charged attract neutral electrons friction contact induction applies push or pull 3 D drawing Electric Fields physists choose that the field would come out a positive change and go into a postive charge direction is determined by which way the electric field would be a positive charge intensity of field is represented by line density more lines = stronger field lines start on a positive charge and end on negative converge onto negative charges and spread/diverge from positive charges Electric Field any charged object creates an electric field of force around it another charged object placed within this field would experience a force of repulsion or attraction Faraday would explain electric force as a charged object sending out an electric field into space, then another charge detects this field when immersed in it - reacting accordingly The electric field at any point is defined as the electric force per unit postive charge and is a vector quanitiy Coulomb's Law the force between two point charges is inversely proportional to the square of the distance between the charges and directly proportional to the product of the charges applies when the charges on the two spheres are small compared to the distance between them Where,
F is the magnitude of the electric force
q , q is the magnitude of the charges on the two objects
r is the distance between the two charges
K is Coulomb's constant at 9.0 X 10 N m / C 2 1 2 2 9 . Electric potential Energy energy can be stored in charges

if you seperate opposite charges; work is done in order for seperation to occur and thus energy is stored

if you push together two like charges; work is done in order for combination and thus energy is stored (negative for attraction; postive for repulsion) Electric Potential V represents the amount amount of work necessary to move a unit of postive test charge from rest to a specific point

The electric potential a distance r from a charge q is given by
Motion of Charged Particles A charged particle in a uniform electric field moves with unifrom acceleration From concervation principles, any changes to a particle's kinetic energy result from corresponding changes to its electric potential energy ( when moving in any electric field and ignorning any gravitational effects. the loss in potential energy in moving a charge away from a field is equal to the gain kinetic energy of the moving charge Robert Millikan spent approx. 6 years determinng the mass of an electron. Magnetic Fields is the area around a magnet in whcih magnetic forces are exerted vector force on current moving objects magnets poles are the regions at the end of a magnetized body at which magnetic attration is the strongest law of magnetic poles
1. opposite poles attract
2. similiar magnetic poles repel Domain Theory principle of electromagnetism sates that moving electric charges produce a magnetic field
How is Magnetism produced? moving electric charges produces a magnetic field, a magentic diople is created by spinning electrons.

a spinning electrons creates a charging electric field that acts as a small current.

electrons either spin up or down.

If electrons are unpaired they create a magnetic dipole
this creates paramagnetic (attracted to magnets) substances.

if the electrons are paired, the spin up cancels down substances are not affected by magnets Properties of Magnetic Field Lines 1. travel from the north pole to the south pole of a magnet on the outside
2. travel from the south pole to the north pole on the inside, creating a continuous loop
3. magnetic field never cross
4. the strength of the magnetic field is indicated by the density of the lines measuring magentic fields the magntidue of the magnetic force, F on a charged particles is: 1. is directly proportional to the magnitude of the magnetic field B, the velocity V and the charge q of the particle.

2. depends on the angle between B and V
if = 90, particle is perpendicular to the field lines
if = 0 or 180, particle is parallel to field lines M Right Hand Rule Effect of Magnetic Fields magnetic force can exert a force on current and moving charges if a charged particle enters a field at an angle ot the field lines, it experiences forces that curves the path of the particle if a charged particle does not escape the path, it will follow a circular path. F = the magnetic force (N)
q = charge of the particle (C)
v = velocity of the particle (m/s)
B = the magnetic field strength (T – this is the Tesla 1 T=1 kg/C µ s)
. = the angle between B and v Force on a wave straight conductor coil Example 1: An electron moves at 4.7 x 10 m/s along the x-axis. It enters a region where there is a magnetic field with a magnitude of 7.2 T, direced at an angle of 65 with the x-axis and lying in the x-y plane. Calculate the inital force of on the electron. Example 2: An electron enters a magnetic field perpendicular to its velocity at 2.5 x 10 m/s. Determine the radius of its circular motion. The magnetic field is 3.5T. Magnetic Fields and Interference Earth's Magnetic Field Earth's magnetic field traps particles from the sun (cosmic rays) as they enter Earth's atmosphere

causing them to spiral around the magnetic field lines connecting Earth's two magnetic poles.

the concentration of incoming particles is higher in polar regions than at the equator, where the charged particles must cross the magnetic fields lines.


Earth has two major radiation belts, areas composed of charged particles trapped by the magnetic field of Earth.

the radiation in these belts are so intense that it can damage sensitive electronic equiment in satellites.

this causes scientists to ensure that all types of spaceships or statellites that they sent up into space avoid these areas, for fear of interference and radiation Earth's magnetic field comes with its disadventages . . . And advantages . . . . it mades it so much more difficult to sent up satellites for the purpose of communication, scientific research and other applications that have now become vital to our daily lives. However . . . it neutralizes Solar Wind! SOLAR WIND is a stream of ionized gases that blows outward from the Sun at about 400 km/second and that varies in intensity with the amount of surface activity on the Sun The Earth's magnetic field help SHIELD the Earth from these solar winds.

For the most part, solar winds are deflected by the magnetic field that surrounds the earth while the high energy particles from the solar winds are trapped in certain regions of the magnetic field that from high radiation betls.

The Earth's magnetic field plays a vital role in protecting life on Earth from solar winds as well as the satellites and internationla space station that are also protected in Earth's magnetic field.

Without the earth's magnetic fields, the satellites that are responsible for a large part of earth's communication system (navigation, television, radio, internet, phone, military purposes) would malfunction in the face of solar winds. Leaving the world with severe concequences.

It would also be very dangerous for astronauts as the radiation from solar winds would likely fatal chromsome damage and cancer.


Everyday Magnetic Interference It's there every single day . . . Significence many of the electronics that are used throughout our everyday lives are suceptable to electromagnetic interfrences. it tends to cause electronic equiment to perform undesirably or fail completely effects on a simple computer monitor (causing distorted images are an inconvience, but failure in medial equiments are fatal Electromagnetic Interference Telecommunication is made possible through radio waves which are traveling electromagnetic waves.

Every wireless communication device including cell phones, radio, GPS tracking devices and satellite communication devices rely on radio waves for transmission and reception of signals.

What leads to electromagnetic interference is the property of these radio waves to superimpose on each other. In the Future . . . motivation for developing/ inventing newer technology and electronics that are less affected by electromagnetic interferences Maglev Trains Revolution of the 21st century Maglev Trains introduction to Maglev Trains maglev is short for magnetic levitation means that these trains will float over a guideway using the basic principles of magnets to replace the old steel wheel and track trains Basically using powerful electromagnets to create high speed trains http://videos.howstuffworks.com/discovery/29341-extreme-engineering-maglev-train-video.htm Making Connections Maglevs are able to travel super fast without the hinderance of friction as they are floating on the tracks. important for highly populated areas (like china and japan) where there is a need to get lots of people from place to place and fast. Maglevs unlike conventional trains do use an engine to pull the train, instead they use the magnetic field created by guildway walls and track this means that they do not require fossil fuels to power the trains any more which results in less greenhouse gases in the atmosphere to contribute to climate change although maglev train require large amounts of electricity to power the trains, however japanese maglev trains use super conducting electromagnets that are able to function even after power is cut off; conserving energy. and as more reasearch is put into maglev trains, it is without a doubt that more energy can be conserved. Economic considerations Maglev trains have a very high captial cost that might not be benificial certain countries at the moment to invest in.
For examples the United states tried to implement a maglev system from L.A to Pittsburg, but found that high start up cost was a huge hinderance.

Mostly, likely because there is no real need for Maglev trains which cars as the main form of transportation in North America. Thus, there woudl be littel economic gain form the trains. However, in countries like China and Japan these Maglev trains are a huge success. With a large population where a main method of transportation is the train, the Maglev trains are a much more profitable investment as there is a garuntee that profit can be made for investors.

For, unlike the united states, countries like China are heaviliy dependent on trains as a method of transportation. Although, with time and technological advancement the cost of Maglev trains will be reduced so that Technology with Maglev trains a reality, there is potential for technology to advance further.

so that science fiction like cover cars and boards might become the reality today if we are able to develope more electromagnetic technology Magnetic Field Therapy scientist discover that external magnetic fields affect the body's functioning in both positive and negative ways. concluded that negative magnetic fields have a beneficial effect on living organisms, whereas positive magnetic fields have a stressful effect. magnetic fields have been known to be able to treat several different symptoms or diseases. magnetic fields can stimulate metabolism and increase the amount of oxygen available to the cells of the body

negative magnetic field applied to the top of the head has a calming, sleep-inducing effect on brain and body functions, due to the stimulation of the production of the hormone melatonin.

A magnetic field can function like an antibiotic in helping to destroy bacterial, fungal, and viral infections



Health Issues radiation produced by magnetic fields might also be able to treat cancer.

Research as found that cancer cannot exist in strong magnetic fields

In conjection with other therapies, it increases the survival of the cancer patients.

however, more research needs to be done before it becomes a more The Human Body the human nervous system utilizies electrical signals to transmite commands from the brain to the rest of the body. the electrical signals are able to travel from neuron to neuron due to a fluxuation of ions in and out of the membrane creating an electrical potential difference. thus the concept of electric potential is necessary for an understanding of the human nervous system and how it can transmit information in the from of electric signals throughout the body. the change in electric potential in neurons produce electric fields that have an effect on the electric potential differences measured at different points on the surface of the body.

By understanding the working of the human body, not only can solutions for certain diseases be found, but monitoring or dignostic equipment be created through the understanding of these principles.

For example:
electrocardiographs would not be possible without a solid understanding of electric potential and electric fields. Significance the activity of the heart muscle causes such electric potential differences; measuring these changes is called electrocardiography.

if the heart is healthy, its regualr beating pattern will produce a predicted change in the electric potential difference between different points on the skin.

doctors can then use this as a diagnostic tool Electrocardiogram helps to catch any cardio problems much faster may be able to save more lives this way along with more accurate diagnosis that would reduce time wasted on figuring out the correct diagnosis

more time and effort can be put into curing the paitent. Electrostatic Precipitators
Are air pollution control devices

They remove tiny particles from emissions (flue gas) of processing and power plants that burn fossil fuels.

Capable to removing approximately 99% of the tiny particles of soot, ash and dust
Electrostatic Prepicitators How It works . . . Dirty flue gas is passed through a series of positively charged plates and negatively charged wires

When a large negative charge is placed on the wires, the electric field near the wire is so strong that it ionizes the air around it.

The freed electrons move towards the positive plates and attach themselves to the tiny waste particles in the flue gas, causing them to become negatively charged and become attracted to the positive plates.

Like, so the plates collect the dust, soot and ash that can be recycled as concrete filling.
This technology relies directly on the properties of the electric fields.



This technology helps to eliminate flue gas which ensures that are air is much cleaner.

This will help reduce health issues caused by polluted air filled with heavy dust and shoot.

For example: breathing in dusts, soot, and ash is highly harmful to our lungs as they cannot be filtered out once they are inside our lungs. This can cause asthma, chronic bronchitis, airway obstruction, and gas exchange

Ash has also been known to contaminate water
and air, leading to damage to the nervous
system and cancer.
Health Significance Environmental Issues Flue gas contributes to carbon dioxide levels and other greenhouse gases that leads to climate change

It also poisons natural ecosystems surrounding the area by contaminating the surrounding water supplies

The electrostatic precipitator will reduce carbon dioxide levels and help protect ecosystems from being contaminated.

Economically there is great potential for this technology, espeically with our society becoming more and more concious of the environmental issues that surrond us.

More companies will be inclined to invest in this technology in exchange for a better public opinon and a clear environment.

This technology has also been adapted to be more consumer oriented; in the form of Plate precipitators or more commonly known as air purifier devices or as a permanent replacement for furnace filters.

As more techological advancements continue, there might be more adaptations and increase the market for this type of products. Electric Field Shielding If the electric field at the surface of a conductor had a component parallel to the surface, electrons would move in response to the parallel component.





If the charges are not moving (in a state of electrostatic equilibrium), the parallel component must be zero and the electric field line must be perpendicular to the conductor
Electrostatic Equilibrium There is a continuous production of stray electric field in the atmosphere; especially during storms or near moving water.

May have remember someone telling you to turn off the tv or computer when there is a thunder storm.

Many household appliances—such as clocks, blenders, vacuum cleaners, and stereos—produce electric fields; monitors and televisions are the biggest producers.

Sensitive electronic circuits, such as those found in computers and in superior tuner-amplifiers, are shielded from stray electric fields by being placed in metal casings.

External electric fields are perpendicular to the surface of the metalcase, zero inside the metal, and zero inside the case.

This effect will shield all the sensitive electric components from electric field.
Shielding Coaxial cables shield electrical signals outside sensitive electric circuits. They are often
used for cable TV and between stereo components (speakers and amplifiers).

A coaxial cable is a single wire surrounded by an insulating sleeve, in turn covered by a metallic braid and an outer insulating jacket

The metallic braid shields the electric current in the central wire from stray electric fields since the external electric fields stop at the surface of the metallic braid.
Coaxial Cables With more and more electronic devices in our everyday lives that each produce their own electric field, more and more devices need to be built with shielding these electric fields from everyday devices in mind.

Electrical field interferences is a huge set back to electronic devices. It is important to ensure that they are properly shielded so that these devices do not malfunction or produce undesirable effects.

In certain situations, where the dependence on these electrical devices are a must, it can be fatal if they were affected by static electric fields.

And there is certainly room for improvement in this technology Electrophoresis Gel Electrophoresis Is the main technology for molecular seperation into today's biology labs.

It is an very powerful but inexpensive technique that is commonly used seperate DNA or RNA or protein Electrophoresis the terms refers to the movement of a charged particle in an electric field.

it is a procedure that enables the sorting of molecules based on size and charge.

By using an electric feild, molecules like DNS can be made to move through a gel made of agar.



The different sized molecules for distinct bands on the gel. larger molecules move more slowly through the gel while smaller molecules move faster catching Criminals
In the case of DNA, the dinstinctive bands created on the gel are unique for every person.

This means that it can be used as a unique fingerprint for individuals.

Having this DNA fingerprint has helped law enforcement locate and convict criminals with much more efficency.

Not only does DNA serve as critical evidence in a trial, it also helps to prevent innocent people from being convicted - as each person will have a different set of bands.

Overall helping to create a safer society! Other Uses Outside of the forensic applications of of electrophoresis, it is also useful in molecular biology, genetics, microbiology and biochemistry.

It has allowed scientists to study the genetic made up of plants, animals and humans in detail.

By fully understanding our gentics, can be find ways to prevent certain genetic disorders or find cures for other diseases.

Magnetic Fingerprint power Magnetic Fingerprint Powder Magnetic powders are best applied to shiny surfaces, such as plastic containers.

works well on plastics and visibility is good, on both light and dark-colored surfaces. used to detect fingerprints that are impossible to check by conventional means. the power consists of tiny iron flakes with an organic ocating that makes them stick to the greasy residue in a fingerprint.

gives sharper results than traditional methods. AS there is no brush with fibers to touch and possibly damage the print.

The powder is not itself magnetic, but is attracted by a magnet and carried as whiskers by a magnetic wand.

Nothing but the powder itself touches the print. Significance Having more accurate fingerprints will help law enforcement, identify, locate and convict the crimial faster.

It can also serve as critical evidence during trial; holding more weight for being more accurate, Overall helping to create a safer society! Example 1: Two charged spheres of mass 0.100 kg are suspended by a string. They are in static equilibrium. Determine the charge on the identical spheres. A diagram is included. Note the length of each side of the string is 0.50 m. A field of force exists in a region of space when an approriate object placed at any point in the field experiences a force. Definition Vectors 24 vibrate places that virbrate are particles different fields Legend since many applications of fields are interconnected and often involve in more than one area of sigificance, multiple symbols will be used as indicators Environment Science technology Economy military society References
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