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 main 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.

 

3. Complete these sentences using the correct variant:

 

1. A parallel circuit has

a) parallel branches only.

b) the main line and parallel branches.

 

2. A parallel circuit is used in order

a) to have the same value of current in all the elements.

b) to have the same value of voltage in all the elements.

 

3. In a parallel circuit a trouble

 a) results in no current in that branch in one branch only.

b) results in no trouble in the whole circuit.

 

4. No current in a parallel circuit

 a) results from a trouble in one branch,

b) results from a trouble in the main line.

 

5. The sum of IR voltage drops

a) equals the value of voltage in the circuit.

b) is less than the smallest voltage drop.

c) is more than the value of voltage in the circuit.

 

4. Complete the sentences using while. Follow the model:

 

Model: Resistors connected in series have the same value of current...

Resistors connected in series have the same value of current while resistors connected in parallel have the same value of voltage.

1. Resistors connected in series have different values of voltage while....

2. A trouble in one element of a series circuit results in no current in the

whole circuit while....

3. In order to have the same value of current in all the elements, a series

circuit is used while....

4. No current in a parallel circuit results from a trouble in the main line

while....

 

5. Answer the following questions:

1. What type of circuit has the main line and parallel branches?

2. What type of circuit is used in order to have the same value of current in all the elements?

3. What type of circuit is used in order to have the same value of voltage in all the elements?

4. What does a trouble in the main line result in?

5. What does a trouble in a branch result in?

6. What does no current in a series circuit result from?

7. How much does the sum of IR voltage drops equal?

8. What is the difference between series and parallel circuits?

5. Pair work. Ask your groupmate to draw and describe a series-parallel circuit.

 

Практическое занятие 4. Измерительные приборы

Lesson 4. Meters

 

1. Read and learn the words:

meter - измерительный прибор

battery - батарея

scale - шкала

readings - показания на шкале (прибора)

terminal - клемма

positive - положительный

negative - отрицательный

to measure - измерять

to take into consideration - принимать во внимание

in this way - таким путем, таким образом

 

Read and translate the text.

 

Meters

Among the most common meters used there are the ohmmeter, the ammeter and the voltmeter. The ohmmeter is used to measure the value of resistance. It consists of a milliammeter calibrated to read in ohms, a battery and resistors. The meter is connected in parallel and the circuit is not opened when its resistance is measured.

The readings on the scale show the measured value. The ammeter is used to measure the value of current. When the ammeter is used the circuit should be opened at one pointand the terminals of the meter should be connected to it. One

should take into consideration that the positive terminal of the meter is connected to the positive terminal of the source; the negative terminal - to the negative  terminal of the source. The ammeter should be connected in series. The readings on the scale show the measured value.

 

3. Complete the sentences using the correct variant:

1. The ammeter is

a) a common meter.

b) an uncommon meter.

 

2. In order to measure the value of current

a) the ohmmeter is used,

b) the voltmeter is used.

c) the ammeter is used.

 

3. A meter has

a) positive terminals only.

b) negative terminals only.

c) positive and negative terminals.

 

4. When the ammeter is used

a) the circuit should be opened.

b) the circuit should not be opened.

 

5. The ammeter should be connected

 a) in series,

b) in parallel.

 

6. One should take into consideration that

 a) the positive terminal should be connected to the negative terminal.

b) the positive terminal should be connected to the positive terminal of the source.