Question

An iron nail behaves as a magnet till it remains close to a magnet

Answer 1

magnetism comes from the region of Magnesia, a city in Western Turkey, where Greeks found lodestones, which attracted iron pieces across the space.   It is also observed that, magnets attract as well as repel.  We can explain this dual nature of magnetic force by proposing that each magnet has two poles, north pole (N) and south pole (S).  You will observe two things during the activities:

1)      When two magnets are brought near each other, like poles repel; opposite poles attract.

2)      When a magnet is brought near a piece of iron, the iron also gets attracted to the magnet, and it acquires the same ability to attract other pieces of iron.

 

We like to represent this force effect of a magnet on iron-like objects with a concept called magnetic field.  The concept of field can be best understood if we remember the gravitational force of Earth on object near it.  We say that the mere presence of Earth sets up gravitational field in the surrounding space, and that we can represent this gravitational force effect with lines starting from Earth and radially diverging away to infinity.

 



Moon is caught in Earth’s field.  Likewise, the Astronaut in space walk is feeling the Earth’s gravity.  Space shuttle is also in the Earth’s field. The reason why they don’t fall is beyond the scope of this course, but I will explain for completeness.  None of them fall towards Earth because they all have enough horizontal speed to make around the Earth.  If you were able to horizontally throw a baseball at 18,000 mi/h, I would also make around the Earth and return to you.  Therefore, we represent the Earth’s attractive gravitational force with field lines.  The direction of field lines represent the direction of force a body would experience around Earth, and the density of field lines (how closely they are separated) represents the strength of the force.  For example, closer you are to the Earth, stronger the force.

Similarly, a magnet sets up a magnetic field in its surrounding space in which it magnetically affects any other magnetic material.  The strength is represented by the density of the magnetic field lines.  Magnetic field lines are closed curves leaving from North pole and entering the South pole when you follow them on the outside the magnet. 

When two magnets are broughtnear each other, like poles repel; opposite poles attract. 2) When amagnet is brought near a piece of iron,the iron also gets attracted to themagnet, and it acquires the same ability to attract other pieces of iron.