Activity 3. Electromagnet in practice. Electric bell
The electromagnet is also part of some important technical equipment:
- electromagnetic relay – it is an electrical switch that is used as a remote-controlled electrical switch operating on the principle of electromagnetism. It consists of an electromagnet, a set of input terminals (metal plates) for single or multiple control signals, and a set of operating contact terminals. The switch can have any number of contacts in multiple contact forms, such as contact making, contact breaking, or combinations thereof.
Relays are used when it is necessary to control a powerful electrical circuit by an independent low-power signal or when several circuits need to be controlled by a single signal. They can protect circuits from overload and short circuit.
Magnetic blocking relays are useful in applications where interrupted power should not affect the circuits that the relay controls.
They were first used in long-distance telegraph circuits as signal repeaters: they update the signal coming from one circuit by transmitting it over another circuit.
Relays were widely used in telephone exchanges and early computers to perform logic operations.
They are widely used in home appliances – stoves, refrigerators, vacuum cleaners, etc.
- circuit breaker to protect appliances from unreasonably high electric currents
Source: https://st2.depositphotos.com/4335179/8125/i/950/depositphotos_81250118-stock-photo-industrial-electrical-component.jpg
- Maglev — a train that uses magnets instead of wheels
Maglev (from magnetic levitation) is a rail transport system whose rolling stock is levitated by electromagnets rather than rolling on wheels, eliminating rolling resistance. There is an air cushion between it and the transport road, so the only friction is with the air.
Compared to conventional railways, maglev trains can have higher top speeds, superior acceleration and deceleration, lower maintenance costs, improved grade control and lower noise. However, they are more expensive to build, cannot use existing infrastructure, and use more energy at high speeds.
The speed record of 603 km/h (375 mph) on such a train was set by the experimental Japanese L0 maglev series in 2015. From 2002 to 2021, the record for the highest operating speed of a passenger train of 431 km/h (268 mph) belongs to the Shanghai maglev, which uses German Transrapid technology. The service connects Shanghai Pudong International Airport and the outskirts of central Pudong, Shanghai. At its historic top speed, it covers the distance of 30.5 kilometres (19 miles) in just over 8 minutes.
Different maglev systems achieve levitation in different ways, which generally fall into two categories: electromagnetic suspension (EMS) and electrodynamic suspension (EDS). Propulsion is usually provided by a linear motor. The power required for levitation is usually not a large percentage of the total power consumption of a high-speed maglev system. Instead, overcoming drag takes the most power. Vactrain technology has been proposed as a means to overcome this limitation.
Despite more than a century of research and development, there are only six maglev trains in operation today – three in China, two in South Korea and one in Japan.
Source: https://upload.wikimedia.org/wikipedia/commons/8/8b/Transrapid_09.jpg
- electric bell as an audible signal
An electric bell is a mechanical or electronic bell that operates using an electromagnet. When an electric current is applied, it produces a repetitive buzzing, rattling or ringing sound. Electromechanical bells have been widely used at railroad crossings, in telephones, firehouses, and burglar alarms, as school bells, doorbells, and alarms in industrial areas since the late 1800s, but are now being replaced en masse by electronic sounders.
Source: https://upload.wikimedia.org/wikipedia/commons/thumb/c/c1/DoorBell_001.jpg/450px-DoorBell_001.jpg
Objectives:
- Familiarise yourself with the working principle of the interrupting bell. It is a mechanical bell that makes a continuous sound when an electric current passes through it. Its operation is described by an animation and a photograph. Examine them and describe the principle of operation.
Source: https://st2.depositphotos.com/1009322/8122/i/600/depositphotos_81227120-stock-photo-alarm-bell.jpg
Source: https://en.wikipedia.org/wiki/File:Electric_Bell_animation.gif
- Connect the different parts of the chime to the correct letter in the picture by completing the interactive exercise:
