Page 156 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

Permeability is the ability of substances to pass magnetic lines of
force through them.

On the basis of your findings can you suggest a method to
increase flux density at a point in a magnetic field?
The magnetic compass is not made by arranging magnetic
needle inside a soft iron case. Why?

Magnetic needles are usually artificial magnets. Alloys are used
to make artificial magnets. How do you make strong magnets
using these alloys?
Electromagnet

Wind a few turns of insulated copper wire on an iron nail.
Connect the ends of the wire to a cell. Bring some pins near the
nail. What do you observe? Why does the nail attract the pins?

Fig. 11.15
Repeat the experiment increasing the number of turns of wire,
increasing the number of cells and using more than one
nail held together. Write down your findings in the science
diary.

Electromagnets can be made by passing electric current through
insulated copper wire wound on a soft iron piece.
The strength of electromagnets made in this way depends on

the number of turns of coiled conductor
the strength of current
the area of cross section of the soft iron placed inside the coil.

All electromagnets are temporary magnets. If the current ceases
to flow, the magnetism of the soft iron core is lost.

Basic Science VIII 155