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Introduction to Electric Circuits and Ohm's Law

Learn about the different types of circuits and how electricity travels through them. Understand the concepts of resistance, voltage, and current, and how they relate to Ohm's Law. Practice drawing circuit diagrams and calculate electric current using Ohm's Law.

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Introduction to Electric Circuits and Ohm's Law

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  1. Pre-AP Physics Types of Circuits and Ohm’s LawAll you need to be an inventor is a good imagination and a pile of junk. -Thomas Edison

  2. Electric Circuits • An electric circuit is something that provides a complete path through which electricity travels. • Wires in electric circuits are similar in some ways to pipes and hoses that carry water.

  3. A Basic Circuit All electric circuits have three main parts • A source of energy • A closed path • A device which uses the energy If ANY part of the circuit is open the device will not work!

  4. How you should be thinking about electric circuits: - a force that pushes the current through the circuit (in this picture it would be equivalent to gravity)

  5. How you should be thinking about electric circuits: Resistance (R): friction that impedes flow of current through the circuit (rocks in the river)

  6. How you should be thinking about electric circuits: - the actual “substance” that is flowing through the wires of the circuit (electrons!) Note: The “I” stands for intensity

  7. Would This Work?

  8. Would This Work?

  9. Would This Work?

  10. The Central Concept: Closed Circuit

  11. Electrical Symbols Circuit diagrams are a short-cut method of drawing circuits. They don’t need to be perfectly draw, but they can be drawn wrong.

  12. Electrical Symbols Paths for electricity to flow. Pushes electricity through circuit. Wire Battery

  13. Electrical Symbols Lights up; resists electricity Resists flow of electricity Resistor Light Bulb

  14. Electrical Symbols Turns electricity on and off. Switch What one would look like.

  15. Simple Circuit When you are drawing a circuit it may be a wise thing to start by drawing the battery first, then follow along the loop (closed) starting with positive and drawing what you see.

  16. Simple Circuits • Series circuit • All in a row • 1 path for electricity • 1 light goes out and the circuit is broken • Parallel circuit • Many paths for electricity • 1 light goes out and the others stay on

  17. Let’s practice drawing the following scenario: • Two light bulbs • One switch • One battery • Wire • series

  18. Let’s practice drawing the following scenario: • Two light bulbs • One switch • One battery • Wire • Parallel

  19. Series and Parallel Circuits • Series Circuits • only one end of each component is connected • e.g. Christmas tree lights • Parallel Circuits • both ends of a component are connected • e.g. household lighting

  20. Series Circuit • In series circuit, the resistors are wired one after another. • Since they are all part of the SAME LOOP they each experience the SAME AMOUNT of current. • See that they all exist BETWEEN the terminals of the battery, meaning they SHARE the potential (voltage).

  21. Voltage Drop Each resistor in a series circuit “uses” part of the energy of the circuit, reducing the voltage. Eventually the voltage is back to zero at the negative side of the battery. Then the battery energizes the electrons again.

  22. Current • Electric current is measured in units called amperes, or amps (A) for short. • One amp is a flow of a certain quantity of electricity in one second. • The amount of electric current entering a circuit always equals the amount exiting the circuit.

  23. There are 2 types of Current DC = Direct Current- current flows in one direction Example: Battery AC = Alternating Current- current reverses direction many times per second. This suggests that AC devices turn OFF and ON. Example: Wall outlet (progress energy)

  24. Current A • This is moving electrons, moving charge. • Increasing current causes more electricity to move through a device. • Increasing electricity through a device causes it to work faster (in a motor) or be brighter ( in a light bulb) B Which bulb would be brighter?

  25. Voltage • Voltage is a measure of electric potential energy, just like height is a measure of gravitational potential energy. • Voltage is measured in volts (V). • A voltage difference of 1 volt means 1 amp of current does 1 joule of work in 1 second.

  26. Voltage • The positive end of a 1.5 volt battery is 1.5 volts higher than the negative end. • If you connect batteries positive-to-negative, each battery adds 1.5 volts to the total. • Three batteries make 4.5 volts. • Each unit of current coming out of the positive end of the three-battery stack has 4.5 joules of energy.

  27. Voltage

  28. Resistance measures how difficult it is for current to flow. Electrical resistance

  29. Resistance • Slows down current. “Think of resistance like a dam holding back water. “ • Adding devices in a circuit increases resistance. • More resistance = less current • Less current = less light

  30. Ohm’s Law I = V/R I = current (amps = A) V = voltage (volts = v) R = Resistance (ohms = Ω)

  31. Calculate time • How much current does a 12 v battery push through a 3 Ω resistor? • V = 12 v • R = 3 Ω • I = ? • 12 v / 3Ω = 4A • How strong a battery produces 2 A through a 3 Ω resistor? • V = ? • R = 3 Ω • I = 2 A • 2 A X 3 Ω = 6 v

  32. An Example and let’s practice VT = 12 V V1 = ITR1 = 2A*1Ω = 2V RT = 6 Ω IT = 2A V2 = ITR2 = 2A*2Ω = 4V V3 = ITR3 = 2A*3Ω = 6V

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