LESSON 5: ELECTRICITY II

Transcription

1 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 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 Technology 1

2 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. Technology 2

3 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. Technology 3

4 -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. Technology 4

5 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. Technology 5

6 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) 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 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. Technology 6

7 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 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 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 Technology 7

8 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. Technology 8

9 3.3. CONNECTING MEASURING INSTRUMENTS - Volmeter measures electrical voltage. It s connected in parallel. Technology 9

10 Exercise 1 Electricity Name:... Date:... Draw the electrical circuit of the following pictures on their right: a) b) c) Technology 10

11 Exercise 2 Electricity Name:... Date:... Draw the electrical circuit of the following pictures on their right: a) b) c) Technology 11

12 Exercise 3 Elektricity Name:... Date:... Draw the electrical circuit of the following pictures on their right: a) b) c) Technology 12

13 Exercise 4 Electricity II Name:... Date: Cross the right answer: a) Which type of connection do these light-bulbs have?: Series. Parallel. Neither of them. b) Which type of connection do these light-bulbs have?: Series. Parallel. Neither of them. c) Which type of connection do these light-bulbs have?: Series. Parallel. Neither of them. d) Which is the voltage of the light bulb in the next circuit: 1,5 V 3 V 4,5 V e) Which is the voltage of the light bulb in the next circuit: 1,5 V 3 V 4,5 V Technology 13

14 f) Which is the voltage of each light bulb in the next circuit: 1,5 V 3 V 9 V 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. The light-bulbs are connected in parallel. The switch is opened. 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. The light-bulbs are connected in parallel. The switch is opened. i) When the switch is closed: All the bulbs are switched on. B 1 is switched on. B 2 is switched on. j) In the next circuit as long as I 1 and I 2 are closed and I 3 is opened: B 1 will light. B 2 will light. All the lights will be switched off. Technology 14

15 k) In the next circuit if I 1 is closed and I 2 is opened: B 1 is on and B 2 is off. All the bulbs are off. B 2 is on and B 1 is off. l) In the next circuit if I 1 is closed and I 2 is opened: The bulb is on. The bulb is off The bulb is burned. m) In the next circuit: B 1 lights, when I 1 and I 2 are closed. B 2 lights when I 1 and I 3 are closed. B 1 lights, when I 1 and I 2 are closed and I 3 is opened. Technology 15

16 n) In the following circuit what should it happen so that the two bulbs are turn on: I 1, I 2 and I 3 should be closed I 1, I 2 and I 4 should be closed and B 3 has to be in good condition. All the switches closed and B 3 in good condition. o) All the switches are closed and B 2 is burned. What will happen? B 1 and B 3 will turn off. B 1 and B 3 will keep on. B 1 will turn off and B3 will remain on. Technology 16

17 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 Current I Amperes Voltage Volts Resistance R Energy Power Symbol of the unit kw.h 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. Technology 17

18 5. Analyse if these circuits will work or not and explain why. a) c) b) d) 6. Complete the table. Position of the switches I1 position 1 I2 open I1 position 2 I2 open I1 position 1 I2 closed I1 position 2 I2 closed Bulb1, B1 Bulb 2, B2 Motor Off Off Stopped Página 18

19 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 Technology 19

20 10. Classify the following materials as conductor, insulator or semiconductor. -Germanium: -Copper: -Silicon: -Plastic: -Wood: -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) Página 20