question_answer

Directions (Q. No. 11 to 15):

Read the following text and answer the following questions on the basis of the same:

Spark coil

The principle of electromagnetic induction was discovered by Michael Faraday in 1831. Induction coils were used widely in electrical experiments and for medical therapy during the last half of the 19th century, eventually leading to the development of radio in the 1890's.

The spark coil designed on the principle of electromagnetic induction was the heart of the earliest radio transmitters. Marconi used a spark coil designed by Heinrich Rhumkorff in his early experiments.

An induction coil or "spark coil" is a type of electrical transformer used to produce high-voltage pulses from a low-voltage (DC) supply. To create the flux changes necessary to induce voltage in the secondary coil, the direct current in the primary coil is repeatedly interrupted by a vibrating mechanical contact called interrupter.

The spark scoil consists of two coils of insulated wire wound around a common iron core. One coil, called the primary coil, is made from relatively few (tens or hundreds) turns of coarse wire. The other coil, the secondary coil typically consists of up to a million turns of fine wire (up to 40 gauge).

An electric current is passed through the primary, creating a magnetic field. Because of the common core, most of the primary's flux couples with the secondary. When the primary current is suddenly interrupted, the magnetic field rapidly collapses. This causes a high voltage pulse to be developed across the secondary terminals due to electromagnetic induction. Because of the large number of turns in the secondary coil, the secondary voltage pulse is typically many thousands of volts. This voltage is sufficient to create an electric spark, to jump across an air gap separating the secondary's output terminals. For this reason, this induction coils are also called spark coils.

To operate the coil continually, the DC supply current must be repeatedly connected and disconnected. To do that, a magnetically activated vibrating arm called an interrupter is used which rapidly connects and breaks the current flowing into the primary coil. The interrupter is mounted on the end of the coil next to the iron core. When the power is turned on, the produced magnetic field attracts the armature. When the armature has moved far enough, contacts in the primary circuit breaks and disconnects the primary current.

Disconnecting the current causes the magnetic field to collapse and create the spark. A short time later the contacts reconnect, and the process repeats.

An arc which may form at the interrupter contacts is undesirable. To prevent this, a capacitor of 0.5 to 15 \[\mu \]F is connected across the primary coil.

The heart of the radio transmitters of Marconi was a

A) spark coil.

B) toroid.

C) RF tuning coil.

D) Van de Graff generator.