Download 49. Rau Alexander Ngatuni, Irene Chuwa and Witness Shirima

Application Of Electromagnets
In An Electric Bell
49. Rau
Alexander Ngatuni, Irene Chuwa and Witness Shirima
Introduction:
An electromagnet consists of a coil of wire wrapped on an iron core and generates magnetic flux when electricity is allowed
to pass through it. The coil forms the shape of the tube which is called as solenoid. If ferromagnetic material is placed inside
the coil much stronger magnetic field can be created. Much stronger magnetic fields can be produced if a "core" of
paramagnetic or ferromagnetic material (commonly iron) is placed inside the coil.
Electric bells help to simplify and support the learning process in school. Apart from schools, it has many applications in
daily life. On our side, making electric bell helps to relate the theory and real life situations. Electric bell reduces the cost of
buying ready made electric bells since we used local available materials to give the same result. For the bell to function
properly it needs to have number of turns of coil which when connected to electricity they create electromagnetism and an
armature made up of soft iron which is attracted by resulting temporary magnetism. The armature must be wounded with
insulated copper wire and not steel iron because steel tend to result into a permanent magnetism a condition which do not
result into ringing.
:
How Electromagnet Works?
Electric current when passes through the soft iron core, produces an energy which is called magnetic flux. If insulated wire is wrapped around an iron or steel object, a
powerful magnetic field is produced. When electricity is passed through a coiled wire a stronger magnetic field is generated. The strength of the magnetic field
depends upon and is directly proportional to the number of coils, the strength of the current, and the magnetic permeability of the core material. Apart from these
factors, the number of turns made by the coil will determine the strength of the field.
MATERIAL AND METHODS
U shaped soft iron core, gang, hummer, Coil copper wire which insulated, Switch, Connecting wire, Adjustable knob
METHODS
Insulated copper wire was wounded on u shaped soft iron (named armature).
Then the armature was attached on a soft board or wooden board.
The adjustable knob was made to contact with the elastic metallic strip.
An elastic metallic strip ends were connected with the Hummer which was close to the hummer.
A connecting wire was connected in a coil then to the battery and adjustable knob. Between adjustable knob and battery a key switch was connected.
When the key was closed the bell started ringing. The problem was that it was stopping ringing after a while. Then we diagnosed and
discovered that the problem was the adjustable knob which pressed the metallic strip so hard is search a way that resulted into permanent
magnetism. After adjustments the sound was better.
To make a bell more efficient, we used soft iron core to make many number of turns of the coil. This produced more electromagnetism in so
doing, a bell produced an excellent sound.
References:
Conclusions:
The bell rang because when the current flowed through adjustable
knob which was in contact with a strip, an electric circuit was
complete. This caused the soft iron core to create
electromagnetism. The electromagnetism created attracted the
strip where by so doing a contact with knob and strip broken and
no more current flowed.
When electromagnetism disappeared it released the strip to its
original position where it reconnected to cause the current to flow
again. This attracted the strip, resulting into vibration which
caused hummer to hit the gang to give the sound.
Further information:
Download at: www.youngscientists.co.tz/posters
http://www.one
school.net/Malaysia/UniversityandCollege/SPM/revisioncard/physics/electr
omagnetism/applicationelectromagnet.html
Nelkons, M. (1981). Principles of Physics, England. Pearson Education
Limited.
TIE. (1995). Physics for Secondary schools. Dar es salaam. Dar es salaam
University Press.
Acknowledgements:
Headmistress and teachers Mr. Felix Puka and Mr. Reve Costa (technical
support).