Vocabulary notes

trial = attempt спроба

lantern [’laentan] ліхтар

subsequent ['sAbsikwant] наступний

circumference [sa'kAmfarans] довжина кола

evacuated chamber вакуумна камера

TASKS

I. Pronounce these word combinations after the speaker and translate them.

Recorded attempt, to travel back and forth, between two hilltops, subsequent trials, human reaction, terrestrial methods, toothed disc, rotational frequency, circumference of a disc, multi-sided mirror, rotating mirror, stationary mirror, rotating period, similar experiments, evacuated chamber, significantly less.

II. Find a synonym (or synonyms) to the first word in each line:

rotate — round, vibrate, move, revolve, improve;

attempt - event, act, perform, trial, vibrate, effort;

travel — go, spread, arrive, move, propagate, cut;

hill - circumference, surface, plane, mountain;

mirror - glass, plate, fork, looking glass, stick;

observe - look, see, hear, watch, investigate, guard;

obtain — go, get, receive, give, translate, write;

place - install, fix, locate, build, distribute.

III. Answer the questions on the text.

1. Who performed the first experiment to measure the speed of light? 2. Did Galileo obtain a time measurement? 3. How did Galileo explain his failure in measuring the speed of light? 4. Who performed the second experiment to measure the speed of light? 5. What method did Olaus Roemer use in his experiment? 6. Who succeeded in measuring the speed of light by a terrestrial method? 7. What was the difference in Fizeau’s and Foucalt’s experiments? 8. What apparatus did Michelson use in his experiment? 9. Is there any difference between the speed of light in air and in other materials?

PROBLEMS

In an experiment similar to that of Michelson’s the correct frequency of a 12-sided mirror is 621 Hz and the distance to the stationary mirror is 20 km. Calculate the speed of light in air from this data.

When walking past a row of shop windows, why can you see yourself in dark windows, but not in brightly lit windows?

Compare and explain the difference in the appearence of stars to astronauts above the Earth’s atmosphere and to astronomers on the surface of the Earth.

If the speed of light in air is 3.00 r 108 m/s, calculate the number of faces on Michelson’s rotating mirror if it has a frequency of 500 Hz and the stationary mirror is 50 km away.

What is the speed of light in a medium if the angle of incidence in air is 50’ and the angle of refraction is 42"?

IV. Read these texts without the dictionary and discuss them with your groupmates.

Albert Abraham Michelson (1852-1931)

Michelson was born in Poland. He emigrated to the Unites States with his parents when he was two.

During his lifetime, Michelson made two major contributions to physics. His work between 1878 and 1927 led to an accurate value for the speed of light. And his investigation with Edward William Morley showed that light travels at exactly the same speed in two mutually perpendicular directions.

Prior to 1887, it was believed that a motionless medium, called ether, existed in space. Scientists postulated the existence of ether to explain the fact that light waves travel from the sun through space. It was thought that all waves require a material medium for their travel.

Michelson hypothesized that if ether existed, then light waves sent in the same direction as the Earth’s motion through the ether should travel faster than light sent perpendicular to it. Michelson and Morley could find no difference in the speeds and hence no evidence for the existence of ether. In 1907, as a result of his work in light, Michelson was the first American to be awarded the Nobel prize for science.