Magnetism

In ancient times Greece people found a rock that attracts iron, nickel and cobalt. They call them as “magnet “and magnetism comes from here. These rocks were used later by Chinese people to make compasses. Later scientists found that, magnets have always two poles different from electricity. Magnets have two ends or faces called “poles” where the magnetic effect is highest. In last unit we saw that there is again two polarities in electricity, “-“charges and “+” charges. Electricity can exist as monopole but magnetism exists always in dipoles North Pole (represented by N) and South Pole (represented by S). If you break the rock into pieces you get small magnets and each magnet also has two poles N and S.
Same poles of the magnet like in the electricity repel each other and opposite poles attract each other.Strengths of these forces depend on the distance between the poles and intensity of the poles.
Types of Magnets
In nature Fe3O4 is used as magnet. However, they can also produced by the people. They can have shapes rod, u shaped or horse shoe. Matters showing strong magnetic effect are called ferromagnetic; matters showing low magnetic effect are called diamagnetic and paramagnetic matters.
Coulomb’s Law for Magnetism
Effects of the two magnets to each other are inversely proportional to the square of distance between them and directly proportional to magnetic pole strenghts of each magnet. These forces are equal in magnitudes and opposite in directions.

F=K(m1m2)/d*d
F1=-F2
Where; k is the constant, m1 and m2 are the magnetic intensities of the poles and d is the distance between them. 

 Magnetic Field
Magnets show repulsion or attraction force around itself. This area affected from the force of magnets called magnetic field. We cannot see magnetic field necked eye. However, if we put a sheet on the magnet and put some iron filing on this sheet we can easily observe the magnetic field around the magnet with the shapes of the iron filling. The shapes of magnetic field lines showed in the picture given below;


Directions of magnetic field lines are showed below;


When the lines get closer to each other, this means that magnetic field is strong in that region.
Magnetic field lines;
  • Never intersect
  • If they are parallel we say that there is a regular magnetic field.
Electricity and magnetism are closely related to each other. Electricity causes magnetic field. Scientists have observed that, when a compass is put next to the wire (wire connected to a battery and current flows), needle of the compass is deflected. The reason of this deflection is magnetic field and they conclude that electric current produces magnetic field. Magnetic field lines around a wire are shown below;                                                           


Magnetic field is a vector quantity and showed with the letter B. Unit of B is Tesla. When we calculate magnetic field of a magnet we assume that there is a 1 unit of m at the point we want to find. We find the magnetic field with following formula;
magnetic field


Magnetic Flux

Magnetic flux is the number of magnetic field lines passing through a surface placed in a magnetic field.
We show magnetic flux with the Greek letter; Ф. We find it with following formula;
Ф=B.A.cosӨ
Where Ф is the magnetic flux and unit of Ф is Weber (Wb) 
B is the magnetic field and unit of B is Tesla 

A is the area of the surface and unit of A is m2

 In the first one, magnetic field lines are perpendicular to the surface, thus, since angle between normal of the surface and magnetic field lines 0 and cos0=1equation of magnetic flux becomes;
Ф=B.A
In the second picture, since the angle between the normal of the system and magnetic field lines is 90º and cos90º=0 equation of magnetic flux become;
Ф=B.A.cos90º=B.A.0=0
Magnetic Permeability

In previous units we have talked about heat conductivity and electric conductivity of matters. In this unit we learn magnetic permeability that is the quantity of ability to conduct magnetic flux. We show it with µ. Magnetic permeability is the distinguishing property of the matter, every matter has specific µ. Picture given below shows the behavior of magnetic field lines in vacuum and in two different matters having different µ.


Comments

Post a Comment

Popular posts from this blog

NUMBER SYSTEMS

Image
NUMBER SYSTEMS In Hindu Arabic System, we use ten symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 called digits to represent any number. This is the decimal system where we use the numbers 0 to 9. 0 is called insignificant digit. A group of figures, denoting a number is called a numeral. For a given numeral, we start from extreme right as Unit’s place, Ten’s place, Hundred’s place and so on. We represent the number 309872546 as shown below: 6-units 4-Tens 5-Hundreds 2-Tounsands 7-Ten thousand 8-Lacs 9-Ten lacs(million) 0-Crocres 3-Ten croces We read it as “Thirty crores, ninety- eight lacs, seventy-two thousands five hundred and forty-six.” In this numeral: The place value of 6 is 6 ×1 = 6 The place value of 4 is 4 ×10 = 40 The place value of 5 is 5 ×100 = 500 The place value of 2 is2 ×1000 = 2000 and so on. The face value of a digit in a numbers is the value itself wherever it may be. Thus, the face value of 7 in the above num
Read more

DC vs. AC

Image
In the Current Electricity section, you learned about electric charge, current, voltage and other related topics. But, just because you have a voltage does not mean electric current will flow. Electrons also need a complete loop of conductive material to flow, called a closed circuit . Let's look at a light switch. When you turn the switch "on", the switch creates a path that conducts electricity and electrons start to move—meaning electric current flows—and the light turns on. As soon as you turn the switch "off", the path is broken and electrons can no longer flow. The switch is like a drawbridge; switching it on is letting down the bridge so the electrons can cross (just like cars crossing a bridge) and provide energy to the light bulb. Illustration of how electric current can move through a closed loop of conductive material (left figure) but stops flowing whenever the loop is broken (right figure). This figure shows how a light bulb l
Read more

Physical quantities, standards and units

PHYSICAL QUANTITIES AND THEIR SI BASE UNITS Following is the list of Physical Quantities and their SI Base Units and Symbols. Physical Quantity Unit Symbol length meter m mass kilogram kg time second s electric current ampere A thermodynamic temperature kelvin K amount of substance mole mol luminous intensity candela cd SOME SI DERIVED UNITS Physical Quantity Unit Symbol area square meter m 2 volume cubic meter m 3 frequency hertz Hz mass density (density) kilogram per cubic meter kg/m 3 speed, velocity meter per second m/s angular velocity radian per second rad/s acceleration meter per second squared m/s 2 angular acceleration radian per second squared rad/s 2 force newton N pressure pascal Pa work, energy, quantity of heat joule J power watt W quantity of electricity coulomb C potential difference, electromotive force volt V electric field volt per meter V/m electric resistance ohm capacitance farad F magnetic flux weber Wb inductance h
Read more