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LESSON 5: ELECTRICITY II

The first two points are a review of the previous lesson

1.1.ELECTRIC CHARGE

- Electric charge is a property of all objects and is responsible for electrical

phenomena.

-All matter is composed of atoms. Atoms are made up of other smaller particles

Protons (+ charge) Neutrons (no charge)

Electrons (- charge)

-Same charges repel each other, different charges attract each other.

1.2. ELECTRIC CURRENT

-Electric current is a continuous movement of electrons.

-Conductor: Materials that allow electric current to pass through them. In general

all metals, and especially copper and silver.

-Insulators: Materials that don’t allow electric current to pass through them.

Plastic, wood or ceramic are insulators.

Electric current in a cable. Copper cable

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1.3. ELECTRIC CIRCUIT

Electric circuit is a set of connected components

through which an electric current circulates.

Electric circuits are made of three elements:

generator (battery), conductor (wire) and receptor

(bulb).

Components of an electric circuit:

-Generator:

-A generator provides the energy necessary to move the electrons. It

produces a permanent electric current. Types: batteries, alternators or

dynamos, photovoltaic solar cells, hydrogen cells.

-Conductor:

-The conductor transports the electric current. Copper wires are commonly used.

-Receptors:

-In a circuit, the receptors are the components that transform electrical energy

into another type of energy:

-Bulbs produce light.

-Bells produce sound.

-Motors produce motion.

-Control and protection components:

-Control components stop, start or change the direction of the

electric current.

The switch is the most common control component.

-Protection components stop the current when it is too strong so that the

important components of the circuit are not damaged.

Fuses are used to protect circuits.

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1.4. REPRESENTATION AND SYMBOLS

A diagram of an electric circuit is a graphic representation using symbols

for the components of the circuit.

Diagram of a circuit using symbols.

The symbols make it easier to draw and follow.

Component Symbol

Battery

Bulb

Motor

Resistor

Switch

Bell

Cable

Push switch

1.5. EFFECTS OF ELECTRIC CURRENT

The energy transported by an electric current can be transformed into other types

of energy:

-Heat: When electrons move through a material, part of the energy is

transformed in heat. This is called Joule effect. The components used to produce

heat are called resistors.

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-Light: Light can be obtained from electricity in three different ways:

a) When an object gets very hot, light begins to appear. At first it is red and

then it becomes white at higher temperature. Incandescent and halogen

bulbs are based on this phenomenon.

b) Some gases emit light when they receive and electric charge. Fluorescent

tubes and low energy bulbs are based on this phenomenon.

c) LED (Light emitting diodes), are tiny devices able to emit light. They are

very efficient but also very expensive.

-Motion: Motors transform electrical energy into motion. They are based on the

forces of attraction and repulsion between a magnet and a conductor wire.

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2. ELECTRIC QUANTITIES

2.1. VOLTAGE, CURRENT AND RESISTANCE

-The charge is the amount of electricity stored in an object. It is represented by

the letter Q and is measured in coulombs (C).

-The voltage is the difference between the electrical energy at two points in a

circuit. The charge always moves from the point where the energy is highest to

the lowest point. If there is not voltage there is not current. Voltage is

represented by letter V ain is measured in volts (V). This is also called tension.

-The current is the number of electrons that pass through a specific point in 1

second (I= Q/t). It is represented by the letter I is measured in amperes or amps

(A).

-The resistance is the opposition of the components of a circuit to the flow of the

electric current. It is represented by the letter R and is measured in ohms (Ω).

QUANTITY NAME SYMBOL UNIT

CHARGE Q Coulomb (C)

VOLTAGE V Voltage (V)

CURRENT I Ampere (A)

RESISTANCE R Ohm (Ω)

2.2. MEASURING INSTRUMENTS

-VOLTMETER measures the electrical voltage. To measure the voltage of a

component you connect the voltmeter in parallel.

-AMMETER measures the current. To measure the current of a receptor you

connect the ammeter in series.

-MULTIMETER measures different electric quantities.

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2.3. ELECTRICAL POWER AND ELECTRICAL ENERGY

-Electrical energy can be transformed into light, heat or mechanical energy. The

amount of energy consumed or produced is called power: P=E/t; P, power is

measured in watts (W) and E, electrical energy in joules (J) or in kW/h (kilowatts

per hour).

2.4. OHM’S LAW

-The proportional relationship between voltage, current and resistance is called

Ohm’s Law, and is expressed mathematically as:

V=I x R

-This shows that current and voltage are directly proportional for any given

resistance.

-Ohm’s triangle will help you this relation.

2.5. RATIONAL ELECTRICITY USE

-Electrical energy is used in most machines and devices we have. This

consumption has a serious impact on the environment. There are three ways we

can help to reduce this impact:

1. Improve the energy efficiency of electrical devices.

2. Reduce consumption.

3. Use renewable energy sources.

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3. CIRCUITS IN SERIES AND IN PARALLEL

-Connection in series: Placing one component after another, so the positive

terminal of each component goes into the negative terminal of the next.

-Connection in parallel: Connecting each component to one of the branches of

the same conductor, so that all the components connect to the same positive or

negative terminal.

3.1. CONNECTING BATTERIES

-When two batteries are connected in series the energy they provide is greater than

only using one battery.

VTotal= V1 + V2; in this case VTotal= 1.5 V + 1.5 V = 3 V

- When two batteries are connected in parallel, the give the voltage but they last

twice longer.

VTotal= V1 = V2; in this case VTotal= 1.5 V

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3.2. CONNECTING RESISTORS/BULBS

-When bulbs are connected in series they share the battery’s voltage.

If one of the receptors in the series stops working, all stop working.

-When bulbs are connected in parallel they receive all the voltage supplied by the

generator.

If one of the receivers turns off /broke the rest continue working.

The more receivers in parallel, the faster the battery will drain.

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3.3. CONNECTING MEASURING INSTRUMENTS

- Volmeter measures electrical voltage. It’s connected in parallel.

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Draw the electrical circuit of the following pictures on their right:

Exercise 1 Electricity

Name: ............................................................................. Date: ...........................

a)

b)

c)

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Draw the electrical circuit of the following pictures on their right:

Exercise 2 Electricity

Name: ............................................................................. Date: ..........................

a)

b)

c)

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Draw the electrical circuit of the following pictures on their right:

Exercise 3 Elektricity

Name: ............................................................................. Date: ...........................

a)

b)

c)

Exercise 4 Electricity II

Name: ............................................................................. Date: ...........................

1. Cross the right answer:

a) Which type of connection do these light-bulbs have?:

.Series ڤ

.Parallel ڤ

.Neither of them ڤ

b) Which type of connection do these light-bulbs have?:

.Series ڤ

.Parallel ڤ

.Neither of them ڤ

c) Which type of connection do these light-bulbs have?:

.Series ڤ

.Parallel ڤ

.Neither of them ڤ

d) Which is the voltage of the light bulb in the next circuit:

V 1,5 ڤ

V 3 ڤ

V 4,5 ڤ

e) Which is the voltage of the light bulb in the next circuit:

V 1,5 ڤ

V 3 ڤ

V 4,5 ڤ

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f) Which is the voltage of each light bulb in the next circuit:

V 1,5 ڤ

V 3 ڤ

V 9 ڤ

g) In a circuit composed by several light-bulbs, as long as one of them is broken and the rest are switched off:

.The light-bulbs are connected in series ڤ

.The light-bulbs are connected in parallel ڤ

.The switch is opened ڤ

h) In a circuit composed three light-bulbs, as long as one of them is broken and the rest are switched off:

.The light-bulbs are connected in series ڤ

.The light-bulbs are connected in parallel ڤ

.The switch is opened ڤ

i) When the switch is closed:

.All the bulbs are switched on ڤ

.B1 is switched on ڤ

.B2 is switched on ڤ

j) In the next circuit as long as I1 and I2 are closed and I3 is opened:

.B1 will light ڤ

.B2 will light ڤ

.All the lights will be switched off ڤ

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k) In the next circuit if I1 is closed and I2 is opened:

.B1 is on and B2 is off ڤ

.All the bulbs are off ڤ

.B2 is on and B1 is off ڤ

l) In the next circuit if I1 is closed and I2 is opened:

.The bulb is on ڤ

The bulb is off ڤ

.The bulb is burned ڤ

m) In the next circuit:

.B1 lights, when I1 and I2 are closed ڤ

.B2 lights when I1 and I3 are closed ڤ

B1 lights, when I1 and I2 are closed and I3 is ڤopened.

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n) In the following circuit what should it happen so that the two bulbs are turn on:

I1, I2 and I3 should be closed ڤ

I1, I2 and I4 should be closed and B3 has ڤto be in good condition.

All the switches closed and B3 in good ڤcondition.

o) All the switches are closed and B2 is burned. What will happen?

.B1 and B3 will turn off ڤ

.B1 and B3 will keep on ڤ

.B1 will turn off and B3 will remain on ڤ

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EXERCISE 5: REVIEW ACTIVITIES ABOUT ELECTRICITY 1. Choose the correct word.

a) Plastic and wood allow/don’t allow electric current to pass through them. b) Insulators are used so that people don’t get electric charges/shocks. c) Electric wires are usually made of copper/rubber and have wooden/plastic

insulation. d) Light switches are usually made of metal/plastic because it is good

conductor/insulator. e) Electric currents are created by the movement of protons/electrons.

2. Complete the table by filling in the missing information.

Quantity Symbol Unit of measurement

Symbol of the unit

Current I Amperes Voltage Volts

Resistance R Energy kW.h Power W

3. What will happen in this circuit if: a) the motor burns out? b) lamp 1 blows? c) lamp 2 blows? d) switch 1 open/closes? e) switch 2 open/closes ? 4. Calculate the resistance of a bulb in a circuit made up of a 6V battery and with a current of 0.5A.

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5. Analyse if these circuits will work or not and explain why.

a) c)

b) d)

6. Complete the table.

Position of the

switches Bulb1, B1 Bulb 2, B2 Motor

I1 position 1 I2 open

Off Off Stopped

I1 position 2 I2 open

I1 position 1 I2 closed

I1 position 2 I2 closed

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7. Draw diagrams with symbols for these circuits:

8. Find the missing quantity, write calculation:

a. V =9V, R=4.5 Ω; I=?

b. R=4 Ω; I=3 A; V=?

c. V=1.5 V; I = 0.5 A; R=?

9. What does the instrument in the photograph measure? a) Current b) Voltage c) Resistance d) All them

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10. Classify the following materials as conductor, insulator or semiconductor. -Germanium: -Plastic: -Copper: -Wood: -Silicon: -Iron: 11. Write the name to each component and draw its symbol.

12. Draw the electric diagrams for the following circuits and identify each symbol

a) b) c)

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