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Bell Ringer

Bell Ringer. You walk up to your friend to give him a high-five for acing his science test. To your surprise, you shock him instead. Why did this happen?. Agenda. NOTES: Current Electric Static vs Current Voltage, Resistance, and Current Ohm’s Law. Current Electricity.

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Bell Ringer

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  1. Bell Ringer • You walk up to your friend to give him a high-five for acing his science test. To your surprise, you shock him instead. Why did this happen?

  2. Agenda • NOTES: Current Electric • Static vs Current • Voltage, Resistance, and Current • Ohm’s Law

  3. Current Electricity • Current electricity is a steady flow of electrons. Unlike static, current is always moving. • There are 3 characteristics of current electricity: • Voltage • Current • Resistance

  4. Voltage (Potential Difference) • The PUSH that makes electrons flow (electrons have potential to flow but won’t on their own) • A difference between energy levels is needed for flow • Electrons flow in a circuit when there is an energy difference from one end of the energy source to the other end of the energy source (like a battery) • Units = VOLTS (V) • 1 Volt = 1 Joule/Coulomb • Symbol = V (capital)

  5. Pop Bottle Demo • Draw a picture and write a description of the demo with the pop bottles for voltage.

  6. Electric Current • The FLOW of electric charges in a circuit • Units = Amperes (amps) • 1 amp = 1 C/s (1 Coulomb of charge moving past a point in 1 second) • Symbol = I • Speed of Current is affected by • Type, length, & thickness of wire • Voltage • When Voltage , Current 

  7. Pop Bottle Demo • Draw a picture and write a description of the demo with the pop bottles for current.

  8. 2 Types of Current • There are 2 types of electrical currents • DC = Direct Current • AC = Alternating Current

  9. DC electricity • Direct current means that the electrons flow in only one direction. • This is the kind of electricity produced by a battery • Electrons come out of the negative end and flow back into the positive end.

  10. AC electricity • Alternating Current electricity means that the direction of electron flow flips back and forth • This is the kind of electricity produced by spinning a generator. • The electricity in homes in the United States changes direction 60 times a second!

  11. Resistance • Opposition to the flow of electrons • Unit = Ohm (Ω) • Symbol = R • Highest resistance in: • Poor conductors • Thin wires • Long wires

  12. Ohm’s Law • Relates Electric Current, Voltage, & Resistance V = I ● R Voltage (volts, V) Resistance (ohms, Ω) Current (amps, A)

  13. Practice Problem 1 Calculate the voltage across a 3Ω resistor if a 0.5 amp current is flowing through it. V = I ●R V = ___________ I = ____________ R = ___________ ? 0.5 amps V = 0.5 amps x 3 ohm’s V = 1.5 volts 3 Ω (ohm’s)

  14. Practice Problem 2 A radio with a resistance of 240 Ω is plugged into a 120 V outlet. What is the current flowing through the outlet? V = I ●R 120 V V = ___________ I = ____________ R = ___________ 120 V = I ● 240 Ω ? I = 120 V 240 Ω 240 Ω I = 0.5 amps

  15. Practice Problem 3 Find the resistance of a circuit that draws 0.06 amps with 12 volts applied. 12 V V = I ● R V = ___________ I = ____________ R = ___________ 0.06 amps 12 v = 0.06 amps ● R R = 12 V 0.06 amps ? R = 200 Ω

  16. Assignments • Review questions and Ohm’s Law calculations

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