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Electric, Magnetic and Gravitational Fields

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Michael Richards

on 13 April 2011

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Transcript of Electric, Magnetic and Gravitational Fields

Fields Describe Force at a distance Visual representation of force around an object Electric Fields Charge: A property that many particles posses. It is unsure as to what exactly charge is, but the 2 types of charges have been named positive (+) and negative (-). Like charges repel, opposite charges attract, and charged objects cab attract some neutral objects. Measured in Coulombs (C) Charge is gained through loss or gain of electrons. Gaining electrons makes a particle more positive, losing electrons makes a particle more positive Charge can be gained by friction (rubbing), induction (electrons moving to one side), contact and induction Law of Conservation of Charge: Total charge within an isolated system is conserved. For example object one has a charge of 7, object two has a charge of 1. When the two objects are touched together, they both have a charge of 4. All particles that have charge attract of repel all other charged particles. Coulombs Law: This attractive or repulsive force (Fe) can be measured by this equation (q=charge, r= distance between particles, k= coulombs constant 8.98x10^9 nm^/C^2) Due to the large size of k, even small charges have noticeable force. This is different from the universal gravitation equation because G is so small, force of gravity can be ignored unless one mass is very large Field Diagram: Visual representation of electric field, defined as electric force per unit charge Denser field lines represent a stronger force on a test object at that point Electric Potential Energy: Energy is stored when two charges are a distance away from each other. Opposite charges will attract, like charges will repel. When any acceleration (attraction/repulsion) occurs, electric potential energy turns into kinetic energy
Electric Potential: Defined as energy per unit of positive charge
Electric Potential difference: difference in electric potential at two points. Differences in electric potential between negatively charged clouds and the positively charged ground causes lightning
The elementary charge is determined to be 1.602x10^-19 C (positive for proton, negative for electron). But how? Connection to STSE Society: Some low level electric fields have been seen to help destroy cancer cells. The electric field destroys cancer cells during cell division, which they are frequently doing. Many patients cancer has gone away completely after using the device which creates the field. Although this is a technological and medical breakthrough and it can lead to the fighting of a terrible disease, the maintenance for this machine is expensive, so it is not for everyone. Technology.: Nerve messages are electrical impulses that move throughout the body. These impulses cause changes in electric potential difference throughout the body. Measuring changes in electric potential difference created by heart muscles is called electrocardiography. This is measured by a special machine called an electrocardiograph or ECG. Measuring potential difference allows healthcare professionals to see a reading of the hearts activity and determine whether the heart is healthy or not. This technology helps lead to the early detection of heart problems and therefore less deaths and a longer living society. Science: Electric fields have greatly helped the field of forensic science. In a process called electrophoresis, Electric fields are used to separate large fragments of DNA based on their charge. This leads to a laid out “map” of the DNA. This can lead forensic scientists to determine murders and other criminals based on DNA evidence left at a crime scene. It can also be useful to ID dead bodies if necessary. Environment: A technology called Electrostatic Precipitators is using electric fields to greatly reduce pollution. In a smokestack, positively charged plate and negatively charged wires are present. A large negative current is sent through the wires, causing electrons to be liberated. These electrons then attach themselves to waste particles such as dust, soot and ash, turning them negative. The particles are then attracted to the positive plates and do not escape into the atmosphere. This technology removes 99% of waste particles, stopping huge amounts of pollutants from entering our atmosphere and ecosystems. Magnetic Fields All magnets contain a north pole and a south pole. Opposite magnetic poles attract, similar magnetic poles repel. A magnetic field exists around every magnet, coming out of the north pole and into the south. Closer together field lines mean a stronger field at that point. The magnetic field of the earth is the reason compasses point north. Domain theory: some special materials called ‘ferromagnetic’ materials, when placed in a strong magnetic fields can become magnetised. This is due to ‘domains’ (similar to mini bar magnets) in the material being realigned by the magnetic field so that all the poles of each domain line up and cause magnetism. Magnetism is also produced by the movement of electric charges. Electromagnetism can be explained by the right hand rules Motion of Charged particle in Magnetic Field: When a charged particle enters a magnetic field, it’s path will curve. If the particle does not enter the field, the particle will move in a circular pattern in the field The force of the magnetic field on a charged particle can be measured by the equation Fm=qvBsin(theta), where q= the charge of the particle, v= speed of particle, B= magnetic field strength in Teslas and theta is the angle at which the particle enters the magnetic field.
Did you know? Magnetic fields can also emit force on a conductive material, and the changing of a magnetic field can produce current in a conductor.
Connection to STSE Society: A technology called Magnetic Resonance Imaging or MRI, uses an extremely strong magnetic field to create images of the body. It does this my lining up hydrogen atoms in the body in the direction of the magnetic field. This releases energy that the machine can detect and use to create an image of the tissue being examined. This picture can then be used to determine if any damage to structures has occurred, or if anything strange or unusual is in the body. This leads to proper disease and injury diagnosis, and also a healthy society. The downside of an MRI scanner is the excessive noise, but the benefits outweigh the negative. Technology: Maglev trains use magnetism in a number of ways. Electromagnetic force is used to levitate the train, so friction is eliminated. The train is also attracted to electromagnets ahead of it and repelled by electromagnets behind it, causing it to move. These trains can move at extremely high speeds and are a great scientific breakthrough. The trains have low maintenance costs, but unfortunately they are extremely expensive to make. Science: The standard model owes many of its discoveries to magnetism. Magnetism is used in particle accelerators to line up and accelerate particles and crash them together at extremely high speeds. Scientists can then observe what particles are emitted by the collision. This is how many fermions have been discovered, and this understanding of the standard model is crucial to understanding how our universe works. Particle accelerators are also very expensive to develop, and there is some controversy around the danger of these particle collisions. Environment: Electricity can be created by switching magnetic fields, producing a current in a conductor. This energy can then be captured and used for daily needs. If scientists find a way to efficiently use this property of magnets, the world energy crisis may be solved. This would also lead to less need for fossil fuels, lessening the greenhouse effect and halting global warming. However, currently this is not a viable method for producing large amounts of energy. Gravitational Fields Gravity is the force of attraction between all objects in the universe with mass. Gavity is responsible for the movement of celestial bodies, as well as objects falling towards the earth. The law of universal gravitation states that the force of gravity (Fg) between two objects is equal to the universal gravitational constant (G) times the masses of both objects divided by the distance between the objects squared. Objects fall to the earth with an acceleration due to gravity of 9.8 m/s^2 Johannes Kepler came up with the laws of planetary motion. What are they? Gravitational Potential energy between objects with mass can be measured with Eg=Gm1m2/r In order to escape from a gravitational field, a mass needs to be moving fast enough, at a speed called the escape speed. Black hole: created after the collapse of a star, has a gravitational field so dense that not even light can escape it. Describe force at a distance Visual representation of forces around an object Connection to STSE Society: Satellites take advantage of the earth’s strong gravitational field, orbiting around the earth. Satellites help send messages such as TV signals and satellite images to various people back on earth. This allows for average households to enjoy TV, programs like Google Earth to exist and even for government agencies to track suspects and see what is happening from an aerial point of view. Satellites benefit society in many ways but can also be very expensive. Technology: Gravimeters measure the gravitational force at different areas across the earth. Based on the strength of the field at a certain area, they can tell the density of the earth and therefore find mineral deposits below the earth’s surface. This leads to mining companies saving money, being much more efficient and being able to cause significantly less harm to the environment. Science: Since gravity is the weakest force, string theorists are pondering why. Some believe that it could be because gravity is made up of one ended strings that are free to escape from our universe and transfer into parallel ones right beside us. If this is true, there could possibly be civilized life right next to us, but they are undetectable. Gravity could be the answer to communication with these societies if they exist. Environment: It is a well known fact that the gravitational pull of the moon causes tides on the earth. This tidal power can be harnessed using underwater devices similar to wind turbines. This allows for the creation of clean, pollution free energy. This form of energy is also extremely reliable, because unlike the wind, tides always occur. However, tidal energy turbines can be very expensive to build and can take up to 10 years to construct. The setup is also bad for local ecosystems and recreation or industry that needs to use the body of water the plant is set up on Works Cited
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