To complete h. to let someone have or do something

To supply i. to finish doing something

To push j. to be greater in number or size

Exercise 2. Practice the reading of the following expressions and translate them into Russian:

Electric current; negative charge; a large number of free electrons; a gap in the circuit; a set number of electrons; a continuous loop; an electrical energy difference; the conducting wire; positive terminal of a cell; cells connected in series; energy transferred by the electrons to the components

Exercise 3. Choose the right answer to the following questions:

C. Yes, it is.

D. Yes, he is.

2. Does an electric current flow in the complete circuit with no gaps?

A. No, it doesn’t.

B. No, they aren’t.

C. Yes, they do.

D. Yes, it does.

3. Can the electrical current flow when the switch is in the “off” position?

A. No, it doesn’t.

B. No, it can’t.

C. No, they don’t.

D. No, it isn’t.

4. Does the battery supply the energy source for the electrons to move?

A. Yes, it does.

B. No, it isn’t.

C. Yes, it is.

D. Yes, he is.

5. Is loose energy passing through lamps in the form of heat and light today?

A. Yes, he does.

B. No, it doesn’t.

C. Yes, it is.

D. Yes, he is.

6. Do the electrons entering the lamp have a lower electrical energy than the electrons leaving the lamp?

A. No, it doesn’t.

B. No, they don’t.

C. Yes, they do.

D. Yes, it does.

7. Is potential difference measured in units called “amperes”?

A. No, it doesn’t.

B. No, they can’t.

C. No, they don’t.

D. No, it isn’t.

8. Do constant collisions make it difficult for the current to flow?

A. No, they aren’t.

B. No, they don’t.

C. Yes, they do.

D. Yes, they are.

9. Did circuit diagrams show the current moving from the positive terminal to the negative terminal?

A. Yes, they did.

B. No, they aren’t.

C. Yes, they do.

D. No, they don’t.

10. Can electrical components be arranged in a circuit either in series or parallel?

A. No, it doesn’t.

B. Yes, they can.

C. No, they don’t.

D. No, it can’t.

Exercise 4. Read the following texts and match them with the titles given below:

Resistance

Parallel Circuits

3. Electric current is measured in units called “Amperes” (amps for short) and has the symbol A.

Series and Parallel Circuits

Electric current is measured by an Ammeter.

6. Conventional Current & Electron Flow

Electric Current

Potential Difference

Text A.

Simply defined, electric current is a flow of electrons. As, electrons are negatively charged, it can be further added that electric current is the flow of negative charge.

In order for an electric current to flow there needs to be complete circuit with no gaps. A basic electric circuit consists of a metallic wire connected to an electrical cell and an electrical component such as a lamp. The metallic wire contains a large number of free electrons that can move easily from atom to atom, it is the movement of these free electrons that give rise to the current.

When the switch is in the “off” position there is a gap in the circuit and the electrical current cannot flow. In the “on” position the switch completes the circuit allowing current to flow and thereby lighting the lamp.

Text B.

1 ampere is a set number of electrons flowing through each point of an electrical circuit per second. 1 ampere is approximately 6 million million million (6 x 10¹⁸) electrons per second flowing past each point. As the charge on electrons is tiny the unit of charge used is the coulomb (C). 1 coulomb is equal to the charge on 6 million million million (6 x 10¹⁸) electrons. Therefore when a current in a circuit is 1 ampere the flow of charge is 1 coulomb per second.

Text C.

By connecting an ammeter in series in an electrical circuit the size of the electrical current can be measured.

It is important to remember that as an electrical current flows through a component such as a lamp or ammeter it is not used up but flows in a continuous loop. The battery supplies the energy source for the electrons to move. These transfer or loose energy when passing through components such as lamps in the form of heat and light but do not get used up themselves. Therefore in series circuit the electrical current is the same in all parts of the circuit.

Text D.

In an electrical circuit the cell (or battery) pushes the electrons around the circuit. It does this by transferring chemical energy from the materials in the cell to electrical potential energy to the electrons. When electrons pass through a lamp in the circuit they give up (lose) some of the electrical potential energy to the thin wires in the lamp in the form of heat and light. Therefore across the lamp there is an electrical energy difference. The electrons entering the lamp have a higher electrical energy than the electrons leaving the lamp. This difference in electrical potential energy across the lamp is called a “Potential Difference or p.d.”

Potential difference is measured in units called “Volts” and has the symbol V. It is for this reason potential difference is sometimes also referred to as voltage.

Potential difference is measured by a Voltmeter.

By connecting a voltmeter in parallel across the component of interest the potential difference across it can be measured (in this case the lamp)

Text E.

Electric current is the flow of electrons. As these electrons flow around a circuit they bump into the atoms in the conducting wire and electrical components. These constant collisions make it difficult for the current to flow or in other words resist the electrical current.

Therefore, Resistance is the property of an object or substance of resisting or opposing the flow of electrical current. Resistance is measured in units called “Ohms” and has the symbol Ω.

Text F.

Electric current is the flow of electrons from the negative terminal to the positive terminal of a cell. This is because electrons are negatively charged and want to move away from the negative terminal and head towards the positive terminal.

When cells were first invented the theory of electron flow mentioned above was unknown. Rather it was incorrectly assumed that the movement was from the positive to negative terminal. Therefore, circuit diagrams showed the current moving from the positive terminal to the negative terminal. We have unfortunately stuck with this convention to this day and so current flow from positive to negative is called, “conventional current flow” and is used when drawing circuit diagrams.

Text G.

Electrical components can be arranged in a circuit either in series or parallel.

Series Circuits

For components connected in series the following rules apply.

1. Electric Current – The electrical current through each component is the same, as all the current has to flow through everything in the circuit.

2. Potential Difference – The potential difference across each component adds up to the potential difference across the battery. This is because the energy transferred from the battery to the electrons must equal the amount of energy transferred by the electrons to the components. The potential difference provided by cells connected in series is the sum of the potential difference of each cell.

Text H.

For components connected in parallel the following rules apply.

1. Electric Current – The total current through the whole circuit is the sum of the current through each electrical component. The current in a parallel circuit branches out after leaving the battery and recombines before entering back in.

2. Potential Difference – The potential difference across each component is the same.

3. Resistance – The combined resistance across the components in parallel is less than either of the separate resistance across the components.

Exercise 5. Find in the texts given above 6 sentences in Active Voice and transfer them into Passive:

Example:

The metallic wire contains a large number of free electrons. – A large number of free electrons is contained in the metallic wire.

Exercise 6. Copy the following text separating it into words and sentences:

Circuit Symbols

Circuitdiagramsareusedtoshowhowelectricalcomponentsareconnectedtogethereachelectricalcomponenthasitsownsymbolinordertodrawbasiccircuitsymbolsitisimportantyoulearnthefollowingsymbols.

Exercise 7. Match components, circuit symbols and functions as it shown in example:

 

Example:

1. E.A., 2.

 

Component	Circuit Symbol	Function
1. Wire	E.	A. Made from a metallic conductor so current can easily pass from one part of the circuit to another

 

Task:

 

1. Wire	A.	A. Made from a metallic conductor so current can easily pass from one part of the circuit to another
2. Switch (open)	B.	B. A battery is more than one cell.
3. Switch (closed)	C.	C. Used to control current.
4. Cell	D.	D. Supplies the electrical energy to the circuit – the larger terminal on the left is the positive (+) terminal
5. Battery	E.	E. Instrument used to measure potential difference.
6. Lamp	F.	F.On/Off switch – in open position the circuit is broken so no current flows
7. Fuse	G.	G. A device which only allows current to flow in one direction
8. Voltmeter	H.	H. Converts heat to electrical resistance
9. Ammeter	I.	I. On/Off switch – in closed position the circuit is complete and current flows
10. Resistor	J.	J. Converts light to electrical resistance
11. Diode	K.	K. Coverts electrical energy to light.
12. Thermistor	L.	L. A safety device which melts to break the circuit if the electrical current flowing through it exceeds a specified value.
13. Variable resistor	M.	M. Restricts the flow of electrical current can be used to limit the flow of current to a particular component
14. Light dependant resistor	N.	N. Instrument used to measure electrical current

 

Exercise 8. Choose the right answers to the following questions:

 

1. What is electric current?

Date: 2015-12-24; view: 992