Mains hum

Mains hum, electric hum, or power line hum is a sound associated with alternating current at the frequency of the mains electricity. The fundamental frequency of this sound is usually 50 Hz or 60 Hz, depending on the local power-line frequency. The sound often has heavy harmonic content above 50–60 Hz. Because of the presence of mains current in mains-powered audio equipment as well as ubiquitous AC electromagnetic fields from nearby appliances and wiring, 50/60 Hz electrical noise can get into audio systems, and is heard as mains hum from their speakers. Mains hum may also be heard coming from powerful electric power grid equipment such as utility transformers, caused by mechanical vibrations induced by the powerful AC current in them.

Causes of electric hum

Electric hum around transformers is caused by stray magnetic fields causing the enclosure and accessories to vibrate. Magnetostriction is a second source of vibration, where the core iron changes shape minutely when exposed to magnetic fields. The intensity of the fields, and thus the "hum" intensity, is a function of the applied voltage. Because the magnetic flux density is strongest twice every electrical cycle, the fundamental "hum" frequency will be twice the electrical frequency. Additional harmonics above 100 Hz or 120 Hz will be caused by the non-linear behavior of most common magnetic materials.

Mains

Mains may refer to:

See also

Mains electricity

Mains electricity is the general-purpose alternating-current (AC) electric power supply. In the US, mains electric power is referred to by several names including household power, household electricity, house current, powerline, domestic power, wall power, line power, AC power, city power, street power, and grid power.

The two principal properties of the electric power supply, voltage and frequency, differ between regions. A voltage of (nominally) 230 V and a frequency of 50 Hz is used in Europe, most of Africa, most of Asia, most of South America and Australia. In North America, the most common combination is 120 V and a frequency of 60 Hz. Other voltages exist, and some countries may have, for example, 230 V but 60 Hz. This is a concern to travelers, since portable appliances designed for one voltage and frequency combination may not operate or may be destroyed by another.

The use of different plugs and sockets in different regions provides some protection from accidental use of appliances with incompatible voltage and frequency requirements.

Hum (Bugojno)

Hum (Serbian: Хум) is a village in the municipality of Bugojno, Bosnia and Herzegovina.

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Coordinates: 44°02′16″N 17°34′03″E / 44.03778°N 17.56750°E / 44.03778; 17.56750

Hum (film)

Hum (Hinedi: हम, English: We/Us) is a 1991 Hindi action crime film directed by Mukul S. Anand. It stars Amitabh Bachchan, Rajnikanth, Govinda, Kimi Katkar, Deepa Sahi, Shilpa Shirodkar, Danny Denzongpa, Anupam Kher and Kader Khan. This was the most successful film for the famous super star, Bachchan in the early '90s before he announced his temporary retirement (for five years) immediately after its release. He also won the Filmfare Best Actor Award for it in 1992. The film ranked second among the top grossers of 1991 at the box office and was declared a blockbuster hit. Mukul S. Anand had considered and discussed a potential scene for this movie with , where Amitabh Bachchan's character would help Govinda get a seat in the Police Academy. Anand discarded the scene, because he did not find it suitable. But felt the scene had the potential to develop into a script for a possible feature film. The discarded scene became the foundation for the 1995 Tamil movie Baashha where character in the film, Manikkam, helps his sister get admission in the medical college she had applied for and it was planned to weave the rest of the film's story around the scene using all the integral key plot elements of Hum.

Hum (Pešter)

Hum (Serbian Cyrillic: Хум) is a mountain on the border of Serbia and Montenegro, between towns of Sjenica and Rožaje, on the eastern edge of Pešter plateau. Its highest peak Krstača has an elevation of 1,756 meters above sea level.

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