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spof.gsfc wikipedia hyperphysic solar hyperhysics Chapter 25General Properties of Magnets
What are some properties of Magents.
A magnet has polarity. the two ends of magnets are called the north Pole and the south poles.
In a magnet two like poles repel, and two unlike poles attract. Earth itself must be a giant magnet because the south pole of Earth's magnet is likely to be near Earths geographic north pole.
Mostly some metals can be polarized by being brought near a magnet. They become temporary magnets.
Many permanent magnets are made of ALNICO,an alloy Aluminum, Nickel, and Cobalt.
Change and Field Convention
Magnetic fileds around Permanent Magnets Magnetic fields is space around a magnet throughout which magnetic force exists.
Forces between magnets, both in attraction and repulsion, do not only happen when magnets touch each other, but it occurs when the magnets are in distance fom each other.
Magnetic Flux: is the number of magnetic field lines passing through a surface. " The flux per unit area is porportional to the strengh of the magnetic field" pg 494The direction of magnetic field lines are define as the direction of which the N-pole of a compass points are no isolated poles on which field lines can start or stop, so magnetic field lines always form closed loops.
Electomagnetism
Hans Christian Oersted was a Danish physicist that was expermenting with elecrtic current wires. What Hans did was Lay his wires across a tip of a small compass. What he was expecting was for the needle to point toward the wire but what happen was that it rotated until it pointed perpendicular to the wire. First right- hand rule is when you grasp the wire with your right hand and you have to keep your thumb pointed in the direction of the positive current flow.
Magnetic field near a coil
When electric current flows through a single circular loop of wire, a magnetic field appears around the loop.
When a current flows through a coil the field around all loops will be at the same direction.
Electromagnt is a device that uses an electric current to produce a concentrated magnetic field. The direction of the field produced by an electromagnet can be found using the second right- hand rule. the way you would do this is to group the coil with the right hand and curl your fingers around the loop in the direction of the current flow.The right hand rule shows the direction of the field produced by an electomagnet.
A microscopic picture of magnetic materials Magnetism in a permanent magnet is the result of magnetic fields of electrons.
The three ferromagnetic elements Iron, nickel, and cobalt behave like an electromagnet, because in the 19 century, a theory of magnetism in iron was proposed by Andre Marie Ampere. He knew that magnetic effects of an electomagent are the result of electric current flowing through loops.
Even though his reasoning was wrong is idea was correct.
The magnetic fields of the electron in a group of neighboring atoms can add together. Such group is called the domain.It may seem that because domains contain 10^-20 individual atoms, they are actually very small.
Sounds or video tape recorders create electric signals, representing the sounds or pictures being recorded. AN iON is a paired of +,- electrons like a manet which is immoblie and a free radical is a single molecule that moves. A free radical is a molecule with an unpaires electron. Because they have a free electron such molecule are higly reactive. ex Singlet oxygen, Free hydroxy group.
Measuring the force on a wire due to a magnetic field
It has been proving that the magnitude of the force on the wire is proportional yo three factors: the strength is represented by the letter "B" OF the field, the current is represented with the letter I, in the wire, and lenght "L" of the wire that lies in the magnetic field.
Magnitude of force is expressed with the equation F= BIL The way you can manipulate the equation to find B is by rewritting the equation to B= F divided IL 1 T(N/A,m) field strenght is a very strong field. "Eath's magnetic field has a strenght of approximately 5*10^-5 T. Earth's magnetic pole to the north magnetic pole". pg 504Galvanometers Galvanometer is a device to measure very small currents. A gavanometer consits of a small coil of wire placed in the strong magnetic filed of permanent magnet. Force on a wire in a galvanometer moves the needle indicating the strenght of the current. Many galvanometers produce a full -scale deflection with as little as 50810^-6 CURRENT. a galvanometer can also be connected as a voltmeter. In order to make a voltmeter, a resistor, called the multiplier is placed in series with the meter. The current is given by ,I= V/R, V is the voltage and R the resistance of the galvanometer.
Electric motors The simple loop of wire used in a galvanometer cannot rotate more than 180 degrees. Electric motors have several rotating loops of wire. The total force acting on the armature is propotional to nBIL. N is the total number of loops, L is the lenght of wire in each loop.
The force on a single charged partice The forc exerted by a magnetic filed on a current carrying wire is a result of the forces on the indvidual charges that add up to the current flow. The force produced by a magnetic field on a single electron depends on the velocity of the electron,the strength of the field and the angle between directions of the velocity at the field. The force on a single electron moving perpendicular to a magnetic field of strength B is F= BIL= b(QV/L) L=BqV
Example Problem
Calculating the strenght of the magnetic field A wire 0.10m long carries a current of 5.0A. The wire is at right angles to a uniform magnetic field. The force on the wire wire is 0.20N. What is the magnitude of the magnetic field, B?
Given F= 0.20N
Unknown: magnetic field strenght b
I= 5.0A
L= 0.10m
Basic Equation B=F/IL
Solution
B=F/IL= 0.25N/(5.0)(0.10m=0.40T
Equations
F=qv x B
F=iBLB
Earth's magnetic field - a discussion of the magnetic field of the Earth. Electric motor - AC motors used magnetic fieldsSources used to complete this project