Portable earphones convert electrical signals into audible sound with the help of a…
PHYSICS · Multi-part · CBSE · Physics · Magnetic Effects of Electric Current · Magnetic Effects of Electric Current
Problem
Portable earphones convert electrical signals into audible sound with the help of a miniature electromagnet placed close to a flexible diaphragm.
(i) Draw a neat, labelled diagram of a simple earphone driver consisting of a coil wound on a soft iron core, a permanent magnet and a diaphragm.
(ii) Describe in proper sequence the physical changes that occur from the instant an alternating current starts flowing in the coil to the production of sound waves in air.
(iii) Explain how Ørsted’s original observation of a magnetic effect produced by an electric current is utilised in the functioning of the earphone driver.
(iv) Show that reversing the instantaneous direction of current in the coil reverses the polarity of the electromagnet, and state how this reversal helps the diaphragm to vibrate rapidly back and forth.