Saturday, December 25, 2010

Practical of Bar magnet for standard 8 to 12

Bar Magnet
Take two bar magnets and mark their north and south poles as explained. Suspend one of the bar magnets using a thread. Bring the north pole of the second magnet near the north pole of the suspended magnet. Observe what happens. Now bring the South Pole of the second magnet near the south pole of the suspended magnet. Observe what happens. Now bring unlike poles of the two magnets close to each other and observe.  Repeat the experiment several times using magnetic needles, generalize your Observation
Bar Magnet Attract
Bar Magnet Repel


Remember 
Like poles of two magnets repel each other
 and
 unlike poles attract each other.
This is called the law of magnetic poles.

Histroy of magnet

A story

Magents of Different types

A story about discovery of magnet is as follows. A shephered Magnus lived at Magnesia in Asia Minor. He noted that the nails fixed to his shoes were attracted by a piece of stone. The stone had the magic property of attracting iron. This stone was called magnet.


Magnetic Axis And Geographic Axis
A freely suspended magnet always points in the North-South direction even in the absence of any other magnet. This suggests that the Earth itself behaves as a magnet which causes a freely suspended magnet (or magnetic needle) to point always in a particular direction: North and South. The shape of the Earth's magnetic field resembles that of a bar magnet of length one-fifth of the Earth's diameter buried at its center.
The South Pole of the Earth's magnet is in the geographical North because it attracts the North Pole of the suspended magnet and vice versa. Thus, there is a magnetic S-pole near the geographical North, and a magnetic N-pole near the geographical South. The positions of the Earth's magnetic poles are not well defined on the globe; they are spread over an area. The axis of Earth's magnet and the geographical axis do no coincide. The axis of the Earth's magnetic field is inclined at an angle of about 15o with the geographical axis. Due to this a freely suspended magnet makes an angle of about 15o with the geographical axis and points only approximately in the North-South directions at a place. In other words, a freely suspended magnet does not show exact geographical South and North because the magnetic axis and geographical axis of the Earth do not coincide.
Cause Of Earth's Magnetism:
It is now believed that the Earth's magnetism is due to the magnetic effect of current which is flowing in the liquid core at the center of the Earth. Thus, the Earth is a huge electromagnet.
Elements Of Earth's Magnetic Field
To understand the Earth's magnetic field at any place, we should know the following two quantities or elements
1. Declination
2. Angle of dip (or Inclination)
Declination
The vertical plane passing through the axis of a freely suspended magnet is called magnetic meridian. The direction of Earth's magnetic field lies in the magnetic meridian and may not be horizontal. The vertical plane passing through the true geographical North and South (or geographical axis of Earth) is called geographical meridian. The angle between the magnetic meridian and the geographic meridian at a place is called declination at that place.
The value of the angle of declination is different at different places on Earth. To find the exact geographic directions (North and South) at a place by using a magnetic compass, we should know the angle of declination at that place. The declination is expressed in degrees East (o E) or degrees West (o W). For example a declination of 2 o E means the compass will point 2 degrees east of true geographical North. Thus, the knowledge of declination at a place helps in finding the true geographical directions at that place. In every map used by surveyors, mariners and air pilots, declination for different places is indicated. It should be noted that at the places of zero declination, the compass North will coincide with the true geographical North.
Angle Of Dip Or Inclination
So far we have only considered one type of magnetic needle which can move only in the horizontal place and points approximately in the North-South direction. Now, if we take a magnetic needle which is free to rotate in the vertical plane, then it will not remain perfectly horizontal. The compass needle makes a certain angle with the horizontal direction. In fact, in the Northern Hemisphere of Earth, the North Pole of the magnetic needle dips below the horizontal line. At any place, the magnetic needle points in the direction of the resultant intensity of Earth's magnetic field at the place.
Angle of Dip at the Poles
The magnetic lines of force at the poles of Earth are vertical due to which the magnetic needle becomes vertical. The angle of dip at the magnetic poles of Earth is 90 o.
Angle of Dip at the Equator
The lines of force around the magnetic equator of the Earth are perfectly horizontal. So the magnetic needle will become horizontal there. Thus, the angle of dip at the magnetic equator of the Earth will be 0 o. The angle of dip varies from place to place.
Magnetic field and magnetic lines of force : Space around a magnetic pole or magnet or current carrying wire within which it's effect can be experienced is defined magnetic field. Magnetic field can be represented with the help of a set of lines or curves called magnetic lines of force.
General Properties of Magnetic Lines of Force
Magnetic lines of force have a number of important properties, which include:
· They seek the path of least resistance between opposite magnetic poles. In a single bar magnet as shown to the right, they attempt to form closed loops from pole to pole.
· They never cross one another.
· They all have the same strength.
· Their density decreases (they spread out) when they move from an area of higher permeability to an area of lower permeability.
· Their density decreases with increasing distance from the poles.
· They are considered to have direction as if flowing, though no actual movement occurs.
· They flow from the south pole to the north pole within a material and north pole to south pole in air.

Magnetism and Electricity, Natural Magnet

Magnetism and Electricity
Concept of manetism-molecular theory, magnetic substances, diamagnetic, paramagnetic and ferro magnetic substance-magnets-artificial and natural-protection of magens-properties of magnets-magnetic field methods of making magnets.

The word magnet is derived from the old French word 'magnete', which in turn is dervied from the Latin word. 'magnes'. It means lodestone or magnet. The property of attraction in lodestone gave rise to its use as magnet. Let us now study about magnets.

Natural magnet

Natural magnet occurs as an ore called magnetic. Magnetic has magnetic properties and does not occur in any regular shape. It behaves like a weak magnet

Natural Magnet

Natural Magnet

Do you Know ?
Chinese were the first people to use the property of magnets to construct Mariner's Compass.

Friday, December 24, 2010

Artificial Magnet Electricity an Magnetism

Do you know 
compass





Chinese were the first people to use the property of magnets to construct Mariner’s Compass.




Artificial magnet
Magnets are useful in many ways. As more and more uses of magnets came to be known, the need for powerful magnets of fixed shape became great. To fulfill this need, powerful magnets of required shapes are made. The powerful magnets of different shapes that are prepared are called artificial magnets. Artificial magnets have regular shapes and required magnetic strength. Artificial magnets are named on the basis of the artificial magnets with their names are shown below.




Bar magnet


Magnetic Needle


Horse Shoe Magnet

Artificial magnets
magnet attracting dollar signs image by Steve Johnson from Fotolia.com
Natural magnets occur in many areas of the world and have been used in China since at least 2,600 BC. These natural magnets are no longer used because it is easy to make artificial magnets. Electromagnets exist only as long as the electricity is on. Non-electric artificial magnets can be more permanent--depending on the material that is used to make them.
Create an artificial magnet by using electricity. When electricity flows through a wire--for example, when the wire is connected to a battery--a magnet field is generated around the wire. You can intensify this magnetic field by coiling the wire so that the overlapping magnet fields reinforce each other. The coil is an artificial magnet as long as the electricity is flowing.
Insert a metallic core into the coil of wire to concentrate the magnetic field. This system of power supply and coil of wire around a metallic core is known as an electromagnet. For most common metallic cores, most of the magnetism goes away when the electricity is turned off.
Construct an electromagnet by attaching both ends of a long wire to a battery and then coiling the center part of the wire around a large nail or a metallic bolt. When both ends of the wire are attached to the battery and electricity is flowing, the metallic core will act like a magnet--picking up small metallic objects. When the circuit is broken--by disconnecting a wire--the small objects will fall. The electromagnet is a magnet only as long as the electricity is flowing.
Make a more permanent artificial magnet by choosing a specially designed substance to make an electromagnet. Two of these substances are alnico and permalloy. If you make an electromagnet using one of these substances--and leave the electromagnet turned on for a while--the core remains magnetic after the electricity is turned off.

How to Make an Easy Electromagnet.
Dry Cell
 
Dry Cell
D Cell Battery image by ike from Fotolia.com
An electromagnet produces a magnetic field through the addition of an electric current. The electricity will flow through a wire. To produce a strong magnetic field in one area, the wire of the electromagnet is coiled around a solid core. The more coils or thicker the wire, the stronger the magnetic field. Electromagnets are used in many devices, such as loudspeakers, generators, magnetic locks, mass spectrometers, relays and transformers. You can create a simple electromagnet with items found at home.
                                                                                        
How to Make An Electromagnet.

Electromagnet
 
Electromagnets are advantageous over permanent magnets in that they can be turned on and off at will. Electromagnets are relatively easy to build if you follow a few steps.

Take the circular piece of metal [magnet] and wind copper wire around it. The windings should be tight and close together
Connect one end of the covered copper wound wire to the output side of a switch.
Connect the negative(black) battery terminal to the negative input terminal on the switch.
Connect the positive battery terminal to the end of the wound wire on the magnet
Check that the circuit is complete, beginning at the negative terminal of the battery to the input side of the switch, then from the output side of the switch to the magnet windings, then back to the positive terminal of the battery.
Turn the switch to on and the magnet will work.
Apparatus:       Circular piece of metal.
 Covered copper wire.
 Switch
 Battery.

Magnetism and Electricity for standard 8 to 10

Scientist

Scientist 
William Gilbert

William Gilbert
1544 – 1603
He was the first person to make a scientific study of magnets. He proved that magnetic poles cannot be separated and Earth acts  as a magnet.

Properties of Magnet

Properties of Magnet 


Bring a powerful magnet near an iron key. What do you observe? Bring an iron key near a powerful magnet. What do you observe? Force of attraction exists between a magnet and iron. Attraction exists between magnet and some other substances like nickel and Alnico also. Verify whether this is true in case you get these substances. What do you learn from this experiment?


Bar magnet Force


Bar magnet Attracts

Remember 
Magnet and a few substances like Iron attract each other.
Properties of Magnet


Take a bar magnet and suspend it from a stand with the help of a thread. Notice the direction in which the ends of the magnet lie as soon as it comes to rest. Now turn the magnet to some other direction and gently leave it. Let it come to rest. Find out whether its ends are pointing to the same directions as before or not. Repeat the experiment using different magnets. What do you infer?
Bar magnet Direction

Remember  
Magnet has the property of indicating the directions when it is freely suspended. Magnet comes to rest in North-South direction.

Properties of Magnet

Take a bar magnet and roll it on iron filings. Did iron filings cling to it? It is quite natural for a magnet to attract iron or vice versa? Now observe the iron filings clinging to the magnet. Do you find iron filings clinging uniformly all over the magnet? In which part of the magnet do you find more iron filings? Do you know why? Repeat the experiment using different types of magnets. What do you infer?

Bar magnet Properties

Remember 
Attraction will be maximum at the ends of the magnet. The ends of a magnet where the attraction is maximum are called the poles of a magnet. Every magnet has two poles-North and South. These ends/poles point to North and South directions.

Wednesday, December 22, 2010

Physics Presentation Student

Physics Innovative
 
Dear Students 
This is the presentation of the science subject which is help full to you to understand science very simply hope you may go through it.