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методические указания для 3 курса..doc
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1. Ответьте письменно на следующие вопросы:

1. What is electricity? 2. What is a magnetic field? 3. What connection is there between electricity and magnetism?

2. Переведите на русский язык следующие словосочетания:

electrification by friction, quantitative measurements, inversely proportional, units of charge, electric field, charged body, magnetic lines of force, static electricity, flow of electrons, chemical energy, electrical resistance, cross-section, difference of potential, in series, in parallel, reciprocal of resistance, free electrons, modern household.

Text 2. Ohm's Law

R= V/I Resistance equals voltage divided by current

I= V/R Current equals voltage divided by resistance

V= IR Voltage equals current times resistance

Problem

V= 1V

I= 1 amp

R=?

Suppose that resistance equals one volt and current equals one ampere. How much is resistance?

Solution

R=V/I, 1V/1 amp = 1 ohm

  1. Solve the following problems using the formulas of Ohm’s Law:

Model: - Current equals 5 amp; resistance equals 10 ohms. How much is the voltage? - Voltage equals current times resistance. 5 x 10 = 50 V

1) R = 80 ohms 2) R=10.25 ohms 3) V=50.05V

V=55V I=35 amp I=120 amp

I=? V=? R=?

4) I=10500 amp 5) V=20.05 V 6) I=0.24 amp

V=2000 V R=0.015 ohm R= 1.36 ohms

R=? I=? V=?

  1. Pair work. Make up similar problems of your own. Ask your groupmate to solve them.

Text 3. Series Circuit and Parallel Circuit

Compare circuits a and b. Circuit a consists of a voltage source and two resistors. The resistors are connected in series. Circuit a is a series circuit.

Circuit b consists of a voltage source and two resistors. The resistors are connected in parallel. Circuit b is a parallel circuit.

A parallel circuit has the mam line and parallel branches.

In circuit b the value of voltage in R1 equals the value of voltage in R2. The value of voltage is the same in all the ele­ments of a parallel circuit while the value of current is different. A parallel circuit is used in order to have the same value of voltage.

In circuit a the value of current in R1 equals the value of current in R2. The value of current is the same in all the ele­ments of a series circuit while the value of voltage is different. A series circuit is used in order to have the same value of current. In R1 V1=IR1 is the voltage drop in R1. In R2 the voltage equals IxR2; IR2 is the volt­age drop in R2. In circuit с a trouble in one element results in no current in the whole circuit. In circuit d a trouble in one branch results in no current in that branch only, a trouble in the main line results in no cur­rent in the whole circuit.