VII. Describe different types of measuring instruments and units, using the table in Task V.
SUPPLEMENTARY TEXTS
Part I
HISTORY OF ELECTRICITY:
OUTSTANDING SCIENTISTS AND DISCOVERIES
TEXT 1
George symon ohm
GEORGE SYMON OHM (1784–1854) is a famous German physicist. In 1805 he entered the Erlangen University. Though he did not graduate from this University, he managed to write and defend a thesis in 1811. Later, he was a teacher at the gymnasiums of Gottstadt and Wamburg. Beginning from 1833 he became professor at the Polytechnical School in Nuremberg, and since 1849 – at the München University.
He is the most famous for establishment of the general law of the electric circuit, stating the relation between resistance, electromotive force, and strength of the current in the electric circuit. The law was discovered experimentally and first formulated in 1826. Further investigations made use of this law. The unit of resistance was named after Ohm at the International Congress of Electricians in1881.
TEXT 2
Ohm's Law
One of Ohm's major contributions was the establishment of a definite relationship between voltage, resistance, and current in a closed circuit. A circuit consists of a voltage source and a complete path for current. Ohm stated this relationship as follows:
Current is directly proportional to voltage and inversely proportional to resistance.
As a formula, it appeals like this:
This formula is commonly known as Ohm's Law.
About 1817 Ohm discovered that a simple correlation exists between resistance, current and voltage. That is: the current that flows in the circuit is directly proportional to the voltage and inversely proportional to the resistance. A current is measured in amperes, a voltage, or potential difference is measured in volts. A resistance is measured in ohms.
Text 3 Faraday's Law
MICHEL FARADAY was a great British physicist, the founder of the theory of electron field, a member of the London Royal Society. He was born in London in the family of a smith. Spending a few years in the primary school, he continued his studies all by himself, reading books and listening public lectures. Greatly impressed by lectures of a well-known English chemist H. Davy, he sent him a letter asking for a job at the Royal Institute. In 1813 Davy gave him a job of a laboratory assistant. Thanks to the brilliant talent of an experimenter, Faraday soon made himself known. All his future scientific work was carried out in the Royal Institute laboratories.
Faraday's law is formulated as follows: (a) the induced E.M.F. in a conductor is proportional to the rate at which the conductor cuts the magnetic lines of force. (b) The induced E.M.F. in a circuit is proportional to the rate of change of the number of lines of force threading the circuit.
Text 4 emil lenz. Lenz's Law
EMIL LENZ was born on the 12 of February 1804 and died on the 29 of January 1865 in Derpt. He became a prominent Russian physicist, an Academician.
At the age of 16 he entered the Derpt University. In 1823, when being a student, he joined a 3 year round-the-world trip on board of the ship “Enterprise” as a physicist. The chief of the expedition was Kotzebu, a famous Russian seaman and explorer. In 1828 Lenz was elected adjunct-professor of the St.Petersburg Academy of Sciences for his outstanding investigations in geophysics.
In the 30 s of the 19th century, Lenz reorganized a physical laboratory of the Academy of Sciences where he began his famous studies on electricity and magnetism. He discovered the law of the electric current emitting heat in conductors. This law laid the foundation for the discovery of the Law of conservation and conversion of energy.
The direction of the induced current is such that its effect opposes the change producing it. The right-hand rule enables one to predict the direction of the induced current, and may be shown to conform with Lenz's law.
The induction coil, the dynamo, the transformer, and the telephone are practical application of electromagnetic induction.