Check your understanding

Exercise 1. True or false?

1. Frequency is the number of wave crests passing a point in one second.

2. When light strikes a mirror at an angle, it is reflected at some other angle.

3. The ratio of the speed of light in space (or in air) to its speed in the substance is always less than one.

4. Diffuse reflection takes place at surfaces that are rough compared with the wave length of light.

5. When the two sides of the glass are parallel, the light emerges in a new direction when it leaves the glass.

6. Light travels faster in empty space and slows down upon entering some matter.

Exercise 2. Choose the correct answer.

1. What is the nature of light?

   1. Light is the form of electromagnetic wave.

   2. Light is a magnetic field.

   3. Light is an electric field.

   4. Light is a stream of molecules.

2. What happens with the light that is not transmitted or reflected?

   1. It is polarized.

   2. It is refracted.

   3. It is scattered.

   4. It is absorbed.

3. At what angles does the light leave an object in diffuse reflection?

   1. The light leaves an object in diffuse reflection at the same angle as it strikes an object.

   2. The light leaves an object in diffuse reflection so, that incident and reflected rays are on opposite sides of the normal.

   3. The light leaves an object in diffuse reflection at many different angles.

   4. When the light leaves an object in diffuse reflection angle of reflection equals to angle of the incidence.

4. When a light ray crosses the boundary between two different materials what does it change?

   1. It changes its speed.

   2. It changes its direction.

   3. It changes its wavelength and frequency.

   4. It changes its wavelength, speed and direction.

5. How many laws of reflection do you know?

   1. 3 Laws

   2. 2 laws

   3. 1 law

   4. 4 laws

Increase your vocabulary

Exercise 1. Arrange the following words in pairs of antonyms.

Negative, light, top, shade, positive, small, diverge, base, more, thin, less, converge, thick, large.

Exercise 2. Translate the following words and word combinations into Russian.

a) recognize, diffuse, finite, converge, join, diverge, curvature, enlargement, truncated, incident;

b) image quality, image formation, light intensity, light diffraction, light propagation, pinhole size, image enlargement, surface curvature, object point, lens axis, light beam;

c) luminous point, straight line, truncated prism, bright image, practical value, coarse pinhole, certain limit, diffuse image, finite size, further enlargement, ground glass, dotted lines, infinite number, opaque screen, fine pinhole.

Exercise 3. Remember the meaning of the terms that you have found in the text.

Focus is a meeting point of rays of light; point, distance at which the sharpest outline is given (to the eye, through a telescope, through a lens, etc.).

Lens is a piece of glass or glass-like substance with one or both sides curved for use in spectacles, cameras, telescopes and other optical instruments.

Prism is a solid figure with similar equal and parallel ends and which are parallelograms body of this form made of glass which breaks up white light into the colours of the rainbow.

Diffraction is scattering of waves in back of a solid object after they strike it.