Acoustics

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.

Hearing is one of the most crucial means of survival in the animal world, and speech is one of the most distinctive characteristics of human development and culture. Accordingly, the science of acoustics spreads across many facets of human society—music, medicine, architecture, industrial production, warfare and more. Likewise, animal species such as songbirds and frogs use sound and hearing as a key element of mating rituals or marking territories. Art, craft, science and technology have provoked one another to advance the whole, as in many other fields of knowledge. Robert Bruce Lindsay's 'Wheel of Acoustics' is a well accepted overview of the various fields in acoustics.^[1]

The word "acoustic" is derived from the Greek word ἀκουστικός (akoustikos), meaning "of or for hearing, ready to hear" and that from ἀκουστός (akoustos), "heard, audible", which in turn derives from the verb ἀκούω (akouo), "I hear".

The Latin synonym is "sonic", after which the term sonics used to be a synonym for acoustics^[ and later a branch of acoustics. Frequencies above and below the audible range are called "ultrasonic" and "infrasonic", respectively.

Explain the following scheme:

Write definitions of the following terms: vibration, sound, ultrasound, infrasound, mechanical waves.

Физика және математика кафедрасының отырысында қаралып, бекітілген.

Хаттама № «7» __18_____ ____03______ 2015 ж.

Кафедра меңгерушісі:____________ Кульжумиева А.А.

Факультеттің ОӘК отырысында қаралып, бекітілген.

Хаттама № «7» __19____ ____03_____ 2015 ж.

Факультеттің ОӘК төрағасы: _________ Иксебаева Ж.С.

М. Өтемісов атындағы Батыс Қазақстан мемлекеттік университеті

Факультет: физика-математика

Кафедра: физика және Физика

Шифр, мамандық: 5В011000 – Физика

Пән: Кәсіби бағытталған шетел тілі

Билет №5

Read and retell the text:

Albedo

Albedo (/ælˈbiːdoʊ/), or reflection coefficient, derived from Latin albedo "whiteness" (or reflected sunlight) in turn from albus "white", is the diffuse reflectivity or reflecting power of a surface.

It is the ratio of reflected radiation from the surface to incident radiation upon it. Its dimensionless nature lets it be expressed as a percentage and is measured on a scale from zero for no reflection of a perfectly black surface to 1 for perfect reflection of a white surface.

Albedo depends on the frequency of the radiation. When quoted unqualified, it usually refers to some appropriate average across the spectrum of visible light. In general, the albedo depends on the directional distribution of incident radiation, except for Lambertian surfaces, which scatter radiation in all directions according to a cosine function and therefore have an albedo that is independent of the incident distribution. In practice, a bidirectional reflectance distribution function (BRDF) may be required to accurately characterize the scattering properties of a surface, but albedo is very useful as a first approximation.

The albedo is an important concept in climatology, astronomy, and calculating reflectivity of surfaces in LEED sustainable-rating systems for buildings. The average overall albedo of Earth, its planetary albedo, is 30 to 35% because of cloud cover, but widely varies locally across the surface because of different geological and environmental features.

The term was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria.