Module in Electric Current-lesson Guideleines pptx

about electric curent

1. ELECTRIC CURRENT Let’s go to our lesson for today ! ANGELICA P. MAGLELONG, MST INSTRUCTOR

2. Contents of the Lesson Electric Battery Electric Current Ohm ’ s Law: Resistance, Voltage and Current Resistivity Electric Power Alternating Current Superconductivity Electrical Conduction in the Human Nervous System

3. LEARNING OBJECTIVES: Explain the transformation of energy Discuss how electric current is produced Solve problems regarding electric current Identify factors that affects the resistance of a wire Illustrate direct current, alternating current and superconductivity Relate electrical conduction in the processes of human nervous system

4. ELECTRIC CURRENT ANGELICA P. MAGLELONG, MST INSTRUCTOR

5. Volta discovered that electricity could be created if dissimilar metals were connected by a conductive solution called an electrolyte. This is a simple electric cell. Electric Battery

6. A battery transforms chemical energy into electrical energy. Chemical reactions within the cell create a potential difference between the terminals by slowly dissolving them. This potential difference can be maintained even if a current is kept flowing, until one or the other terminal is completely dissolved . Several cells connected together make a battery, although now we refer to a single cell as a battery as well. Electric Battery

7. — Gregory Dickow “ Faith is like electricity. You can't see it, but you can see the light .”

8. Electric current is the rate of flow of charge through a conductor. Unit of electric current: the ampere, A. 1 A = 1 C/s What is an electric current?

9. ELECTRIC CURRENT A complete circuit is one where current can flow all the way around. Note that the schematic drawing doesn ’ t look much like the physical circuit.

10. Ohm’s Law - How Voltage, Current, and Resistance Relate DEFINITION Current It is the rate of flow of charge through a conductor Resistance a measure of the opposition to current flow in an electrical circuit. Voltage A n electromotive force or potential difference expressed in volts. UNITS Ampere (A) is for current, Volts (v) is for voltage, Ohms ( Ω ) for resistance.

11. SAMPLE PROBLEM In this first example, we will calculate the amount of current (I) in a circuit, given values of voltage (V) and resistance (R):   I = V/R OHM’S LAW EQUATION In this algebraic expression, voltage (V) is equal to current (I) multiplied by resistance (R). Using algebra techniques, we can manipulate this equation into two variations, solving for I and for R, respectively:   R = V/I

12. Some clarifications: Batteries maintain a (nearly) constant potential difference; the current varies. Resistance is a property of a material or device. Current is not a vector but it does have a direction. Current and charge do not get used up. Whatever charge goes in one end of a circuit comes out the other end. EXERCISES: Solve for the unknown quantity ( V , I, or R) given the other two, and express your answer in both scientific and metric notations and kindly illustrate also. 1. I = 825 A, R = 15.0 mΩ; V = ? 2. V = 750 mV, R = 86 Ω; I = ? 3. V = 30.0 V, I = 0.0025 A; R = ?

13. - The thinner the wire, the more resistance it offers. Thicker wires offer less resistance - The longer the resistor, the more resistance it has. The shorter the resistor, the less resistance it has. FACTORS THAT AFFECT RESISTORS What determines the resistance of a component? Let's investigate some of the factors. There are 4 different factors which affect resistance : The thickness of the resistor The length of the resistor The type of material of which the resistor is made The temperature of the conductor Thickness of a conductor Length of the conductor

14. The type of material of which the resistor is made - Conductors can be made of different materials Temperature of the conductor The hotter a resistor becomes the more resistance it has. The atoms of the conductor vibrate much faster when they are hot due to the increase in kinetic energy. You can see that the filament is made up of coils of tungsten wrapped up tightly. We want to fit a very long wire into a small space. The electrons have to travel through this very long, high-resistance wire.  A close-up photograph of the tungsten filament in an incandescent light bulb.

15. RESISTIVITY It is the resistance of the flow of current from one end to the other in a material. Electrical resistivity is a simply accessible and informative quantity to describe the material. It is the reciprocal of electrical conductivity. The resistivity is represented as ρ and it is directly proportional to the material resistance and length. Resistivity is inversely proportional to the area of cross-section of the given material.

16. Resistivity The resistance of a wire is directly proportional to its length and inversely proportional to its cross-sectional area: The constant ρ , the resistivity, is characteristic of the material.

17. ELECTRIC POWER Power, as in kinematics, is the energy transformed by a device per unit time: The unit of power is the watt, W. SAMPLE PROBLEM What is the resistance of a 100m length of round copper wire with a radius of 0.3mm? Kindly work on your virtual spaces and solve!

18. Power in Household Circuits The wires used in homes to carry electricity have very low resistance. However, if the current is high enough, the power will increase and the wires can become hot enough to start a fire. To avoid this, we use fuses or circuit breakers, which disconnect when the current goes above a predetermined value. For ohmic devices, we can make the substitutions: What you pay for on your electric bill is not power, but energy—the power consumption multiplied by the time. We have been measuring energy in joules, but the electric company measures it in kilowatt-hours, kWh. One kWh = (1000 W)(3600 s) = 3.60 x 10 6 J

19. Fuses are one-use items—if they blow, the fuse is destroyed and must be replaced. Circuit breakers, which are now much more common in homes than they once were, are switches that will open if the current is too high; they can then be reset.

20. Thanks! You can always attracted to what you’ve learn, see you in the next lessons!