chapter 19 - magnetism Flashcards
properties of magnets
- region where the magnetic attraction is the strongest is known as the poles of a magnet
- freely suspended magnet will always point in the north-south direction
- obeys laws of magnetism
law of magnetism
like poles repel, unlike poles attract
magnetic field
a region where a force of magnetism acts on a magnetic material
test for magnet?
hang a permanent magnet on a retort stand until it stabilizes. bring the metal bar to each end of the magnet and observe what happens. if both ends of magnet attracts the metal bar, the metal bar is a magnetic material. if only one end of the magnet attract the metal bar while the other one repels it, the metal bar is a magnet. (repulsion is the only way to test for magnetism)
how to induce magnetism
- place material near strong magnet
(materials such as iron and steel are attracted to magnets because they themselves become magnetised in the presence of a magnet. induced magnetism is temporary) - stroking method
(the first side the pole touches becomes the pole) - using an electric current
placing the magnetic material in a coil of wire (solenoid) carrying a d.c current
determining magnetic field pattern
- iron filling method
(putting too much iron fillings with make the magnetic field pattern unclear) - plotting compass method
direction of field line
the direction of field line at any point is taken to be direction of the force acting on a “free north” pole placed at that point of time
properties of magnetic field patterns
- magnetic field lines formed closed loops
- neutral points : magnetic field intensities cancel each other and leave no resultant force
using iron vs steel
iron is soft and easy to magnetise but easy to lose its magnetism, steel is hard and difficult to magnetise, but it is able to retain its magnetism for a longer period of time
iron is normally used as a temporary magnet but steel is normally used as a permanent magnet
