Electric Current

1. Electric Current Chapter 13

2. What is Electricity?

3. Some Key Terms: Conductor: Allows Electricity to flow easily Insulator: Does NOT allow electricity to flow easily Potential Difference: A difference in Electrical Potential Energy. Also called Voltage or an Electromotive force (EMF)

4. What is a circuit An electric circuit is a closed conductive path with a power source, for electricity to flow.

5. Potential Difference: We have seen Potential before…where….What does it mean? Where can you find Potential for electricity…?

6. What is potential difference? A voltmeter must be connected in parallel because it measures the potential difference across the component. V Potential difference is a measure of the difference in electrical potential energy between two points in a circuit. Potential difference is also calledvoltage. Voltage is measured involts (V)using avoltmeter. The voltage of a battery or cell is a measure of the force or “push” it gives the current. A 1 V cell gives 1 joule (J) of energy to each coulomb of charge. So, a 12 V battery gives 12 J of energy to each coulomb of charge.

7. What can we measure in a circuit? - Voltage • Voltage • Is a measure of __________ ________ _________. • When there is a voltage difference; there is _______ _____ ____ _____. • The Volt has a unit of ____. • Example: a 9 Volt battery has an electrical potential energy difference of _____.

8. A An ammeter must be connected in series because it measures the current flowing through it. What is current? Current is a measure of the rate of flow of electric charge in a circuit. Electric charge is measured incoulombs. Howis current measured? Current is measured inamperes (A) using anammeter. This unit is named after Andre Ampere, one of the early scientists to study electricity. A current of 1 A is 1 coulomb of charge flowing every second. So, a current of 5 A is 5 coulombs of charge flowing every second.

9. What can we measure in a circuit? - Current • Current What it actually means! • When there is a potential difference (V) electrons will flow in the circuit. • The electrons FLOWING is the actual _________. • We say the current flows from the + end to the – end of the battery. • The symbol for current is I and the unit is A (ampere or amp)

10. “Viva La Resistance!”- Eric Cartman What is Resistance…in a circuit? Resistance is a measure of how hard it is for electrons to move in an electrical circuit. • Symbol is R and it’s unit is Ω (Ohm). -If we add things to a circuit like an light bulb, it is harder for electricity for flow through it, increasing the resistance.

11. Water model of a circuit

12. Battery and Bulb Can you make a bulb light using only a bulb, a D-cell battery and one piece of wire? Draw a picture of all the ways you have tried to light the bulb. Identify which ones worked and which did not.

13. 1 step back, 2 steps forward • Current Electricity- The FLOW of electric charge. Charge flows from higher potential to lower charge potential (more on this later) • Q: How do we describe current flow?

14. How did you light the bulb? Congratulations! You made a circuit!!!, but what is a circuit?

15. You built this… BUT…we would draw it like this… OR

16. Symbollogy…How to draw circuit diagrams

23. Without the simple symbols, We would have to draw complex Pictures like this…

24. Current Flow • Circuit-The path or paths which current flows. MUST BE COMPLETE! • Conventional Current-How electrons would flow if they had a positive chargefrom Positive to Negative • Current cannot flow through an OPEN circuit

25. Closed circuit Vs Open Circuit Closed Circuit Open Circuit

26. Electric Current Summary • Electrons in motion, move from +  - • Current: The number of electrons that pass a specific point in a circuit in one second • Current is brought to us by the letter I I = Q/t Q-Charge (Coulombs (C)) t-Time (Seconds (s)) • Circuit: electric current flows through a closed, continuous path.

27. Units and Examples • SI Units for Current is the Ampere (Amp)(A) • From the equation I = Q/t we see 1 A = C/s • Ex: A charge of 3 coulombs moves through a circuit in .5 seconds. What is the current in the Circuit?

28. Conditions for current • For current to flow one needs 2 things: (think back to the bulbs) • A closed path of conducting material. This path is called a _____ • A difference of potential (electric charge) between two points in the circuit.

29. Potential Difference/Voltage • Remember, another name for Potential Difference is Voltage emf • Voltage is the difference in electrical potential between two places where e¯ are flowing • Voltage is what “pushes” the electricity through the circuit. • But HOW????

30. Stuff you know!  Explain the following diagram: How does this relate to a circuit?

31. Jumping back to Electricity • Think of the Current as water. Water flows from Higher PE to lower PE • Eventually the water settles and “loses” its energy • The pump acts like a battery, because it brings the water from Low E to High E • Battery keeps charge difference so that current continues to flow.

32. How much Current? • The amount of current flowing through a circuit depends on 2 things: • How big the voltage is (how hard the electrons are being pushed • How big the resistance is. • What is resistance?

33. How do you measure current and voltage Ammeter (smart wire) Voltmeter

34. Resistance • Resistance- degree of opposition (sort of like friction) that charges encounter as they move through a conductor, measured in Ohms (Ω) • HUH? • Can you use the water analogy to explain this in English? • How can we have a small resistance?

35. Ohms Law • Voltage = Current X Resistance V=IR • The Real lyrics to Twinkle Twinkle Little Star! • Twinkle Twinkle Little Star, Voltage= I x R A second verse, coming soon  Practice Problems!