1. Electric Current
Chapter 7 – Section 2

2. Electric Current - The unit for current is amps (A)
Flow of electrons through a wire.
Current

3. Types of Current Ways in which electrons flow DC – direct current
Electrons flow in same direction in a wire
Ex. Battery
AC – alternating current
Electrons flow in both directions in a wire
Ex. Power cords

4. Direct Current - battery http://www. energizer
Batteries produce electrons through a chemical reaction.

5. Alternating Current - generator
Electrons are produced at a power plant and sent through wires to homes & businesses.

6. Amount of current depends on :
Voltage – the push behind current flow: measured in (V) volts.
Resistance – the amount of friction between the electrons and the wire: measured in (Ω) ohm’s
Low Resistance = good conductors
High resistance = poor conductors or Resistors
The amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to oppose electron flow.
Carpet vs. Hardwood

7. Calculating Current Current is calculated using Ohm’s Law
Current = Voltage
Resistance

8. Calculating Current Quantity Symbol Unit Abbreviation Current I Amps A
Voltage V
Volts
Resistance R
Ohms Ω

9. Calculating current

10. Practice
How much current is in a circuit that includes a 9-volt battery and a bulb with a resistance of 3 ohms?
How much current is in a circuit that includes a 9-volt battery and a bulb with a resistance of 12 ohms?

11. Practice
What is the voltage of a circuit with 15 amps of current and toaster with 8 ohms of resistance?
How many ohms of resistance must be present in a circuit that has 120 volts and a current of 10 amps?

12. Circuits - Path through which charges can be conducted
Closed Circuit =complete path - bulb WILL light up
Open Circuit = incomplete path - bulb will not light up

13. Parts of a Circuit Voltage source – battery Wire - conductor
Resistor – bulb, buzzer, motor
Switch – open/close circuit (optional)

15. Draw a circuit with … 1 battery & 1 light bulb & 1 resistor
If the battery is 9 volts, the light bulb is 2 ohms, and the resistor is 1 ohm – what is the current of this circuit?

16. Types of circuits Two types of circuits: Series – ex: Christmas lights
Parallel – ex: House

17. Series Circuits Series – single path for charges to flow
If one element removed, circuit will not work
Voltage across each device can be different – second bulb may have less voltage – light is dimmer

18. Parallel Circuits Parallel – multiple pathways
Voltage across each device is the same
Each resistor uses what it needs
Can remove one element without interrupting flow

19. Is the following series or parallel?
Series – all components are on the same path
Parallel– all components are on their own path

20. Draw your own circuit
Draw an open series circuit with 1 light bulb, 2 resistors, and a switch
Draw a closed parallel circuit with 2 light bulbs and a switch

21. What is the total voltage of each circuit? A = B =

22. Magnets

23. Let’s see what you
know about magnets!

24. 1.
Magnets not only pull things, but they can also push things away.
A. true
B. false

25. A. true

26. 2.
The Earth is one big giant magnet.
A. true
B. false

27. A. true

28. 3.
Two magnets with like poles will
_________ each other.
A. attract (pull together)
B. repel (push apart)

29. B. repel (push apart)

30. 4.
Two magnets with unlike poles will
_________ each other.
A. attract (pull together)
B. repel (push apart)

31. A. attract (pull together)

32. 5.
Compasses always point in
which direction?
A. North
B. East
C. South
D. West

33. A. North

34. 6.
The space around a magnet is
called its ____________.
A. electrical field
B. baseball field
C. magnetic field

35. C. magnetic field

36. 7.
Magnets will only be attracted to
objects that have this in them.
A. silver
B. copper
C. iron
D. gold

37. C. iron

38. 8.
Magnets can even work in water.
A. true
B. false

39. A. true

40. You are now an expert on magnets!
Congratulations!
You are now an expert on magnets!

41. What is a magnet?
A magnet is an object that attracts certain materials - usually objects made of iron or steel.

42. A magnet has two ends called magnetic poles or just poles for short.
A magnet’s pull is strongest at the poles.

43. magnetism Magnesia, province of Greece
Unusual property of lodestone noted over 2000 years ago

44. 12th C, Magnets first used in navigational compass, Chinese

45. 16th C, William Gilbert
“Every magnet has two poles, a north and a south.”
“Like magnetic poles repel, unlike poles attract.”

46. Figure 5-5(a)
A bar magnet and its magnetic dipole field.

47. Figure 5-3
A compass needle and the Earth. Any magnet will twist because of the forces between its poles and and those of the Earth. Every magnet has at least two poles.

48. Courtesy Andy Washnik
Figure 5-5(b)
Iron filings placed near a bar magnet align themselves along the field.

49. Figure 5-4
A magnetic field. Small magnets placed near a large one orient themselves along the lines of the magnetic field, as shown.

50. “Opposites attract. Likes repel.”
The above describes both magnetic and electric force, but
electric charges can be isolated,
magnetic poles cannot.

51. Figure 5-6
Cut magnets. If you break a dipole magnet in two, you get two smaller dipole magnets, not an isolated north or south pole.

52. Magnets have Poles
Just like the Earth has a North and South Pole, magnets also have two poles.
This is because the Earth is actually a HUGE magnet itself!
Similar magnetic poles repel, while opposite magnetic poles attract.

53. Magnets have a Magnetic Field
Every magnet has a magnetic field around it. It can be thought of as a line of force running from the north end of the magnet to the south end of a magnet.
Earth’s magnetic field is what causes the needle of a compass to point north and south.

55. 1820, Hans Oersted
…connected a battery to let electric current flow, and noticed a compass needle twitch and move.

56. Electricity & Magnetism: “ two sides of the same coin “
Every time an electric charge moves, a magnetic field is created.
(electromagnet)
Every time a magnetic field varies, an electric field is created.
(motor)

57. Electric motors convert electricity into magnetic fields, for useful rotary motion

58. Figure 5-8
An electric motor. The simplest motors work by placing an electromagnet that can rotate between two permanent magnets.
(a) When the current is turned on, the north and south poles of the electromagnet are attracted to the south and north poles of the permanent magnets. (b)–(d) As the electromagnet rotates, the current direction is switched, causing the electromagnet to continue rotating.

59. Electric motors convert electricity into magnetic fields, for useful rotary motion

60. Electrical Generators
…are the exact opposite of electric motors: they convert rotary motion into electrical energy.
link

61. Figure 5-10
An electric generator. As long as the loop of wire rotates, there is a changing magnetic field near the loop and a current flows in the wire.

62. Electric Motor M
Electrical
Energy
Mechanical
Energy
DC Motor

63. Electromagnetic Devices
Motors
Converts electrical energy into mechanical energy
Commutator – split ring, allows current to change direction every ½ revolution
Brushes – connect wires to commutator
2/19/2019
Physical Science

64. Electric Generator G Mechanical Electrical Energy Energy
Stationary magnets - rotating magnets - electromagnets

65. Generators Converts mechanical energy to electrical energy
Loop turns within a magnetic field
On each half rotation the current reverses direction – alternating current
2/19/2019
Physical Science