Electricity Electric circuits - презентация

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2 Electricity Electric circuits and circuit symbols Ohms Law Series and Parallel Circuits

3 The students will able: to explain how electric current flows in a circuit to wire a basic circuit to take measurements of voltage and current intensity in a circuit to explain the difference between series and parallel connections

4 The Electricity is the physical phenomena associated with the flow or movement of electric charge.

5 Electric charge as a fundamental property of some subatomic particles. Inside an atom there are: - Protons have a positive charge - Electrons have a negative charge - Neutrons have no charge (neutral)

6 Particles of opposite charges are attracted to each other Particles of like charges are repelled The SI (Systeme International) unit for charge is the coulomb (C) It takes 6.25 x protons to equal one coulomb!

7 A conductor is something which freely allows the motion of electric charge. An insulator is the opposite; it greatly resists the flow of charge. Conductors eg. Copper cable Water – Gold Silver – Platinum Metals Insulators eg. Plastic sheet Rubber – Ceramic Wood

8 Electric current is the ordered flow of negative electric charge. Typically the negative electric charge is electrons. In fact conventional current, which is what is used by all electrical engineers, is the flow of positive charge. conventional current flow of electrons

9 In a conductor the electric charges they are free to move, then the conductor resulting in electric current In an insulator the electric charges they are not free to move, then there is no passage of electric current

10 The SI unit of Intensity of electric current ( I ) is the Ampere (A). Ampère is equal to a flow of one coulomb per second. Intensity current is measured with an ammeter Digital ammeter (digital multimeter) has a digital display Analogic ammeter has a graduated scale

11 Current can only flow in the presence of an electric field, often provided by a voltage source (eg. Battery or Cell). Voltage is the electric potential between two points (V). It is the electric potential to cause an electric current to flow.

12 Voltage is measured with a voltmeter. The SI unit for voltage is the volt (V). Volt measure how strongly an electrical current is sent around an electrical circuit. Digital voltmeter (digital multimeter) has a digital display Analogic voltmeter has a graduated scale

13 How many volts are in a AA battery? 1.5 V the wall outlet? 230 V the power lines in the street? about 13,000 V the large power lines? up to 765,000 V lightning? about 100,000,000 V

14 Define the electric circuit as a connection of two or more components to form a closed loop. The closed loop is necessary to allow the electric current to flow from one point of the voltage source to the other.

15 Electric resistance is a physical property which describes how well electric current flows in a material.

16 The SI unit for resistance is the ohm ( Ω ) The resistor has resistance equal to 1 when, subjected to a potential difference of 1V, it is transmitted a current of 1A. Electric resistance is measured with an ohmmeter Digital ohmmeter (digital multimeter) Analogic ohmmeter

17 Voltage = Resistance Current The voltage V between the ends of a metallic conductor is directly proportional to the intensity of the current that runs through it. One therefore has: where the coefficient of resistance of the conductor R is constant with changing V. Ohms Law is a formula used to calculate the relationship between voltage, current and resistance in an electrical circuit.

18 If two of these values are known, technicians can reconfigure Ohms Law to calculate the third. Just modify the pyramid as follows: If you know current (I) and resistance (R) and want to know voltage (E), multiply the bottom halves of the pyramid

19 If you know voltage (E) and current (I) and want to know resistance (R), X-out the R in the pyramid and calculate the remaining equation If you know voltage (E) and resistance (R) and want to know current (I), X-out the I and calculate the remaining equation

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21 Define electric power as the rate at which electrical energy is transferred. The SI unit for power is the watt (W). P V I Power = Voltage Current Voltage = Power / Current Current = Power / Voltage The pyramid

22 In a series circuit, electric current has only one path to follow. All parts are connected one after another. Electrons flow from the negative side of the battery around in a loop to the positive side.

23 Series components are connect in line with each other. they share the same current Components in series have the same current They divide the voltage among themselves Components in series have different voltages The different voltages add up to the original total voltage of the voltage source

24 In a parallel circuit, electric current has more than one path to follow. Electrons can follow different paths as they flow from the negative side of the battery to the positive side.

25 Parallel components are connected side by side. Each component provides a different path for the current to flow Components in parallel have different currents The different currents add up to the current in the voltage source Components in parallel have the same voltage