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Understanding Ohm's Law: Calculating Current, Voltage, and Resistance

Learn about Ohm's Law, the relationship between current, voltage, and resistance in electrical circuits. Practice calculating current, voltage, and resistance using Ohm's Law.

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Understanding Ohm's Law: Calculating Current, Voltage, and Resistance

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  1. Ch. 20 - Electricity IV. Electrical Circuits & Power (p.706-714) Ohms Law Series circuits Parallel circuits Power

  2. Things you should already know or be able to do… Construct a simple electrical circuit using wires, batteries and light bulbs. Can you do this??? You need to do this to pass this weeks test on Electricity

  3. Learning Target: Describe the relationships between current, voltage, and resistance.

  4. Current, Voltage & Resistance Electricity & Water Analogy: Pressure in a hose (V), rate the water flows through the hose (I) and the diameter of hose ( R) are all related. If you change one, it affects the others The relationship is known as Ohm’s Law… Voltage = Current x Resistance V = I x R

  5. Ohm’s Law Visual: Relationship between V, I and R http://phet.colorado.edu/sims/ohms-law/ohms-law_en.html

  6. Learning Target: Use Ohm's Law to calculate current, voltage, and resistance using correct units.

  7. Ohm’s Law

  8. E. Ohm’s Law • Ohm’s Law V: potential difference (V) I: current (A) R: resistance () V = I × R • Voltage increases when current increases. • Voltage decreases when resistance increases.

  9. V R I E. Ohm’s Law • A lightbulb with a resistance of 160  is plugged into a 120-V outlet. What is the current flowing through the bulb? GIVEN: R = 160  V = 120 V I = ? WORK: I = V ÷ R I = (120 V) ÷ (160 ) I = 0.75 A

  10. Practice: There is a potential difference of 12 volts across a resistor with 0.50 amps of current in it. The resistance of the resistor is _________. 0.5 ohms 6 ohms 12 ohms 24 ohms

  11. Practice: If there is a current of 6 amps flowing through a 3 ohm resistor, what is the potential difference in the circuit? 0.5 volts 2 volts 9 volts 18 volts

  12. Practice: If a circuit has a potential difference of 120 volts and a resistance of 10 ohms, what is the current that flows through the circuit? 0.08 amps 12 amps 120 amps 1200 amps

  13. Practice: A bunch of science students get together every Friday night for a science party. Last Friday, they watched a couple of episodes of Bill Nye the Science Guy. They used a TV requiring 2.00 amps and a DVD player requiring 0.50 amps and they used 120V outlets. What is the resistance of the TV? 12 ohms 60 ohms 240 ohms 1200 ohms

  14. NEED Ohm’s Law Worksheet Complete today in class (We’ll review in 15 minutes)

  15. Practice:

  16. Learning Targets • Describe the difference between a series and parallel circuit. • Contrast how voltage and current are applied to light bulbs in series vs. parallel circuits.

  17. A. Circuit Components A - battery C - light bulb B - switch D - resistor

  18. What are electric circuits? Circuits typically contain a voltage source, a wire conductor, and one or more devices which use the electrical energy. What is a series circuit? A series circuit is one which provides a single pathway for the current to flow. If the circuit breaks, all devices using the circuit will fail.

  19. What is a parallelcircuit? A parallel circuit has multiple pathways for the current to flow. If the circuit is broken the current may pass through other pathways and other devices will continue to work.

  20. What is the difference between an open circuit and a closed circuit? A closed circuit is one in which the pathway of the electrical current is complete and unbroken. An open circuit is one in which the pathway of the electrical current is broken. A switch is a device in the circuit in which the circuit can be closed (turned on) or open (turned off).

  21. B. Series Circuits • Series Circuit • current travels in a single path • one break stops the flow of current • current is the same throughout circuit • lights are equal brightness • each device receives a fraction of the total voltage • get dimmer as lights are added

  22. C. Parallel Circuits • Parallel Circuits • current travels in multiple paths • one break doesn’t stop flow • current varies in different branches • takes path of least resistance • “bigger” light would be dimmer • each device receives the total voltage • no change when lights are added

  23. A. Electrical Power • Electrical Power • rate at which electrical energy is converted to another form of energy P: power (W) I: current (A) V: potential difference (V) P = I × V

  24. A. Electrical Power • A calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use? GIVEN: I = 0.01 A V = 9 V P = ? WORK: P = I · V P = (0.01 A) (9 V) P = 0.09 W P V I

  25. D. Household Circuits • Combination of parallel circuits • too many devices can cause wires to overheat • Safety Features: • fuse - metal melts, breaking circuit • circuit breaker - bimetallic strip bends when hot, breaking circuit

  26. Assignment • Read pages 706 – 714 • Complete the Electrical Circuits and Power Review Handout • Due Thursday 6/12

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