A Siren in Emergency Service Vehicles (Level 3)

Written by Saurav
Description: An article about s police siren on their cars

Instructions: Read the short article below and answer the questions or fill in the spaces.

A siren is a device that makes a loud noise. It is used to get people’s attention. Sirens are used today in emergency service vehicles like ambulances, police cars and fire trucks. Most of the sirens are also used during a natural disaster or civil defence incident to alert people to danger.
There are two types of sirens. That is a pneumatic siren and an electronic siren. These sirens are mounted on the top of a vehicle. A pneumatic siren consists of a rotating disk with holes in it. As the holes in the rotating disk alternately prevent and allow air to flow it results in alternating compressed and rarefied air pressure which makes the sound. Electronic sirens are made up off circuits. The main components are oscillators, modulators and amplifiers.