- •Part I
- •Text. Physics and physical phenomena
- •Laboratory Exercises
- •Additional Material
- •M. V.Lomonosov
- •Exercises
- •Laboratory Exercises
- •Additional Material
- •Measurement of Volume
- •Text. The metric system
- •Dimensions of a Solid Body
- •Laboratory Exercises
- •Additional Material
- •Origin of the Metric System
- •Text. The kinetic theory and the three states of matter
- •3 Not to matter — не иметь значения will make full use — займут
- •Exercises
- •Laboratory Exercises
- •Additional Material
- •Text. Mass and weight
- •3. Much, more, the most; little, less, the least; good, bet ter,
- •4, .,. Er than, more ... Than
- •5. At, on, over .., etc.
- •Exercises
- •Laboratory Exercises
- •Additional Material
- •Text, force, work, energy and power
- •Exercises
- •Additional Material
- •1. Have supported, has altered....
- •2. Energy can be converted...
- •Exercises
- •Laboratory Exercises
- •Additional Material
- •Isaac Newton
- •Text. Heat
- •1. Heat is known to be a form of energy.
- •2. You place, you placed, you have placed. They take, they took, they have taken.
- •3. Newton began to think about heat.
- •Exercises
- •Laboratory Exercises
- •Additional Material
- •Text. Transmission of heat
- •Exercises
- •Laboratory Exercises
- •Additional Material
- •Good and Bad Conductors of Heat
- •Text. Calorimeters
- •1. It is usual to transfer ...
- •2. There is; is there; there is no ...
- •3. The setting up of ...; the reading of ...
- •Exercises
- •Laboratory Exercises
- •Additional Material
- •Text. Wave motion and sound
- •1. It does not move forward but returns again...
- •2. It is evident, it is clear.
- •Exercises
- •Additional Material
- •Text. Light
- •1. It becomes red-hot, it is the reason, it was cold...
- •2. High temperature produced by..., in a substance called... . Exercises
- •Laboratory Exercises
- •Additional Material
- •Text. Reflection and refraction of light
- •1. Do bodies emit? Does he make? Did it represent?
- •2. Have they shown? Had he travelled? Was it reflected? Is he going? Exercises
- •Laboratory Exercises
- •Additional Material
- •Text. Lenses
- •1. After leaving the lens...
- •Exercises
- •Additional Material
- •Text. Simple cell
- •1. The twitching of; the reading of...
- •Exercises
- •Laboratory Exercises
- •Additional Material
- •Voltaic Cells
- •Text. The accumulator
- •1. A plate containing, a plate being immersed...
- •2. Achieved by connecting; determined by testing...
- •Exercises
- •Additional Material
- •Text. Principle of electric motor
- •1. They are used to pull...
- •2. When viewed, while doing...
- •Exercises
- •Laboratory Exercises
- •Additional Material
- •Electric Bell Circuit
- •Text. Moving-coil ammeter and voltmeter
- •Exercises
- •Laboratory Exercises
- •Additional Material
- •Moving-Coil Galvanometer
- •Text. Electromotive force
Text. Lenses
Lenses are bodies made of transparent material and bounded by faces having a cylindrical or spherical form. Although lenses differ much in form they may be divided into two classes according to the way in which they act on a parallel beam of light. Consider the lens in Fig. 5, a on which parallel rays are incident. Each ray is bent toward the
Fig. 5. Principal foci of simple lenses.
normal to the surface on entering the lens and away from the normal on emerging from the lens. In this way, the rays above the axis PO are bent downward and those below it are bent upward. After leaving the lens, the rays converge to a point F, called the principal focus. Such a lens is a converging lens. If the incident rays are parallel to each other, the incident wave front is a plane perpendicular to the incident rays. When this wave front emerges from the lens, it has been changed to a concave wave front that converges to the focus. When the bounding surfaces of the lens are very convex, the lens converges the rays rapidly. This gives the lens a short focal length. When the bounding surfaces are slightly convex, the lens has a long focal length. In order that all the rays may come to a point after leaving the lens,
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the beam of light must be restricted to a narrow bundle near the principal axis of the lens. For an extended beam the outer rays will not pass through the same point as the rays near the axis. When the surfaces of the lens are concave instead of convex, the lens makes the rays that pass through it more divergent, and for this reason it is known as a diverging lens. In Fig. 5, b parallel rays are incident on a concave lens. On entering the lens, the rays are bent toward the normal "as before, and on leaving they are bent away from the normal. In this case, however, the emerging rays are bent away from the principal axis. They appear on leaving the lens to come from a point F behind the lens. When the incident rays are parallel to each other and to the principal axis, this point from which the rays appear to come on leaving the lens is the principal focus. This is only an apparent focus because the light does not really come from it, but the effect on the left-hand side of the lens is the same as if the light actually came from this point behind the lens. This kind of focus from which the light appears to come is a virtual focus. It is to be carefully distinguished from a real focus through which the light actually goes.
If the lens is convex, and the incident rays come from a point source, the incident wave front is spherical, and the emerging wave front is the surface of a sphere with its centre at the image. If the lens is concave, the curvature of the wave front is increased in passing through the lens, and the image is behind the lens.
Listen and read words and word combinations to be remembered:
transparent [traens'pearant] concave [ konkeiv] вогнутый
прозрачный convex ['konveks] выпуклый
emerge [i'me:dj] выходить restrict [ris'trikt] ограничивать
converge [kan've:dj] cxo диться extend [iks'tend] расширяться
bundle ['bAndl] пучок diverge [dai've:dj] pacxoДИТЬСЯ -
apparent [a'paerant] мнимый virtual ['vetjual] действительный
image ['imidj] изображение normal ['no:mel] перпендикуляр
bound [baund] граничить curvature ['ke:vatja] изгиб
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principal focus главный фокус
converging lens собирательная линза
diverging lens рассеивающая линза
bounding surface граничная поверхность
focal length фокусное расстояние
principal axis оптическая ось
emerging wave front выходящий фронт волны
incident wave front падающий фронт волны
real focus действительный фокус
point source точечный источник
Give Russian equivalents to the following words without using a dictionary:
lenses ['lenziz] parallel ['paralel]
material [ma’tieriel] perpendicular [ ,pe:pen'dikju la]
cylindrical [si'lindrikal] outer ['auta]
spherical ['sferikal] effect [i'fekt]
form [fo:m] pass [pa:s]
front [frAnt] focus [foukas]
Models