The flow of electrons

1. The flow of electrons M Tommasi

2. Electric current Static electricity is the…….. The flow of e- in a wire is called an electric current More e- implies greater current. It is measured in Amperes (amps) The symbol is the letter “I”

3. Resistance It is the opposition to the flow of electrons. It is what makes some wires better conductors. It changes electricity into light or heat It is measured in ohms The symbol is “R”

4. Voltage To move object we need to push them Electrons can be pushed also That push is called voltage The bigger the push the higher the voltage It is measured in volts The symbol is “V”

5. Donow • Give an example of a load. • What does a switch do to a circuit? • What is the main difference between a series and a parallel circuit? • Draw a series circuit containing a power source, a switch and 2 loads? • What happens in a series circuit that contains a power source, a switch and 2 light bulbs if one light bulb blows out?

6. Reviewing • Current (I) is the flow of electrons in a circuit • Voltage (V) is how hard the electrons are pushed • Resistance (R) is the “friction” of electric flow.

7. Possibilities • Can you have • A) high current and high voltage? • B) high current and low voltage? • C) low current and high voltage? • D) low current and low voltage?

8. Ohm’s law • A locomotive can push a train of cars against friction at a velocity. • If there’s a lot of friction it can push only a few cars • To push a lot of cars it has to push harder • The amount of push a locomotive can provide depends on the friction and number of cars.

9. Ohm’s law • In electricity voltage is the locomotive • The voltage equals the current x resistance • V = I x R • If there’s more resistance you have to push harder • If you want to move more electrons you have to push harder

10. Problem 1 • A voltage has to push electrons through a load or resistor • Problem: What voltage is needed to push a current of 5 amps through a light bulb that has a 4 ohms resistance inside it? • V = I x R • V = 5 x 4 = 20 volts

11. Question 2 • What is the current going through a wire that has a resistance of 30 ohms if the voltage pushing the electrons is 45 volts? • V = I x R • 45 = I x 30 • I = 45/30 • I = 1.5 ?

12. Donow • What is voltage? • What is current? • What is resistance? • What voltage is necessary to push 3 amps of current through a 4 ohm resistor? • What current can go through a 5 ohm resistor if 4 volts are pushing it?

13. Electrical power • The power needed to run an appliance depends on the voltage and the current • Every appliance needs a different amount of power to work • Power = voltage x current • P = V x I • In the US the voltage in any regular outlet is always 120 volts

14. Example • How much power is used by a light bulb if the voltage across the light bulb is 120 V and the current going through it is 2 amps? • P = V x I • P = 120 x 2 = 240 watts.

15. example • What power is being used by a hair dryer if the current going through it is 10 amps? • Power = voltage x current • Power = 120 x 10 • Power = 1200 watts

16. Two types of current • Electrons can be pushed in 2 different ways • They can be pushed out directly from one point and go into another (DC or Direct Current) • The electrons can be made to go back and forth (AC or Alternating Current)

17. Creating DC (direct current) • DC can be created in several ways • 1) wet cell-using liquid acid and two different metals to chemically release electrons • Car batteries are a kind of wet cells • 2) dry cell-using an acid paste instead of liquid acid to release electrons • These are the regular “batteries” • Cells always have a voltage of 1.5 V

18. Creating a DC current • 3) battery- a group of cells working together • That’s a 9-volt battery • 4) Solar cells- pure silicone sheets that use sun light to push electrons

19. Creating (AC) alternating current • A magnet is moved back and forth near a wire • As the magnet moves the electrons are pushed back and forth • The current changes direction • In the US the current changes direction 60 times a second (60 Hz)

20. Creating alternating current • AC current is made by blocking a river (Dam) and allowing the escaping water to turn a turbine (hydroelectric). • Or by boiling water and letting the steam turn the turbine • The heat to boil the water can be made by burning coal, oil or nuclear power.

21. Electrical safety • Never handle an appliance with wet hands or while standing in water • Never run wires under a carpet • Don’t connect too many appliances to the same circuit • Get rid of extensions if they are damaged • Never stick metals inside electrical appliances • Never come too close to fallen power lines.