As the Ebola virus outbreak continues to run amok in West Africa, scientists are looking ahead to the possibly pivotal use of experimental drugs and vaccines against the disease. It will take months to test, produce and deploy the therapies. But researchers hold out hope that these products — even incompletely vetted — might help to turn the tide against an illness that has defied public health efforts to bring it under control.

Thursday, 14 June 2012

Construction of Electric Bell

ELECTRIC BELL
 

MAIN COMPONENT OF
ELECTRIC BELL

    Important parts of an electric     bell are :
    1. Electromagnet
    2. Armature
    3. Spring
    4. Armature rod
    5. Hammer
    6. Gong
CONSTRUCTION
    One end of armature winding is connected to terminal T1 and the other to a spring, which is mounted on     a soft iron strip. A rod is attached to the armature and the free end of the rod carries a small hammer,     which strikes a bell. A very light spring is attached to a screw, which is joined to terminal T2.
WORKING OF ELECTRIC BELL
    The electric circuit is completed through a battery and push switch button connected to the terminal T1     and T2. When the push button is pressed the electric circuit is completed and the armature is attracted     towards the electromagnet as a result, the small spring gets detached from the screw due to which the     electric circuit is broken and the electromagnet is demagnetized. Hence, the attraction disappears and     the armature is brought back by the spring to its original position. Contact of the spring with the screw is     now remade, which completes the electric circuit. The action is repeated over and over again     consequently. The armature vibrates and hammer attached to it strikes the gong and the bell rings and     sound is produced.
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