1. Electricity & Magnetism How are electricity & magnetism related?

2. Warm-up: True or False? Magnets attract all metals.
If you cut a magnet in half, one end will be a north pole, the other end will be a south pole.
North poles are made of positive electric charges, and south poles are made of negative electric charges.

3. Conventional Current vs. Electron Flow
Electron Flow Model:
Electrons flow from the negative terminal to the positive terminal of the source.
Conventional Current:
From Benjamin Franklin’s Kite Experiment
Positive charges were thought to carry current

4. Relating Electricity & Magnetism
When a current flows through the wire, you should have noticed that this causes the needle of the compass to move perpendicular to the wire. Watch This
What does this imply?

5. Oersted’s Discovery
Hans Oersted first related electricity and magnetism in when he noticed that the needle of a compass deflects when placed closed to a current carrying conductor
Oersted’s Principle:
Electric charges moving through a straight conductor generate a circular magnetic field around the conductor
Current flows from positive to negative

6. Oersted’s Discovery… The field around a straight conductor:
Forms concentric circles around the conductor
Has a direction that depends on the direction of the current
Has a strength that decreases the further you are from the conductor
Gets stronger when the current is stronger

7. Oersted’s Discovery…
Cross section of the field around a straight conductor (note how the field weakens further away from the wire):
The shaded inner circle represents the cross-section of a straight conductor carrying a current. You can imagine that the X is the tail of an arrow and is moving away from you. This indicates a current that goes into the page. You can imagine that the dot is the tip of an arrow that is facing you. This indicates a current that goes out of the page.

8. Use right hand rule for a straight conductor
How can you predict the direction of the magnetic field around a line conductor?
Use right hand rule for a straight conductor
Rule is based on the flow of conventional current
To apply the rule:
Current flows from positive to negative
1. Point your thumb in the direction of conventional current flow
2. Your fingers curl in direction of the magnetic field

9. Relating Electricity & Magnetism
Watch this video until 0:17.
What will happen when the switch is pulled?
Nothing
The wires will always be attracted
The wires will always be repelled
Sometimes they will attract, and sometimes they will repel

10. Relating Electricity & Magnetism
In the video, what happened when the switch is pulled?
When in series, the wires repel
When in parallel, the wires attract

11. Coiled Conductors?
Use the right hand rule to predict what the magnetic field will look like in each case. The + and – signs show the direction of conventional current.

12. Coiled Conductors? Look Here

13. Coiled Conductors A solenoid is a coiled conductor.
The magnetic field created by a current flowing through a solenoid is similar to the field of a bar magnet. Electromagnets are electrically powered bar magnets, that can be turned on and off by turning the current on and off.
The field of an electromagnet can be increased by:
Increasing the number of loops in the coil
Increasing the current
Introducing a core made of a material that can be magnetized

14. How can you predict the direction of the magnetic field produced by a solenoid?
Use right hand rule for a solenoid
Based on the flow of conventional current
To apply the rule:
Wrap your fingers in the direction of the conventional current flow
Your thumb will point north
Current in the coil
Number of loops
Type of core material (e.g. air, iron…)

15. Recall: Magnetic Domains
Domains in a non-magnetized material
Domains in a magnetized material

16. Strength of an Electromagnet

17. Magnetic Field of a Solenoid
Rank the magnetic field just outside the RIGHT end of the electromagnet from largest to smallest. (Some may be equal.) Explain your ranking!

18. Magnetic Field of a Loop Magnetic Field of a Series of Loops
Hypothesize: Use the right hand rule to predict what the magnetic field will look like in each case.
current flow
current flow

19. Homework
Pg. 556 #1, 2, 3, 5, 6, 7
Pg. 562 #1, 2, 3, 4, 7
Read and take notes on Pg. 561, “Applications of Solenoids”
Really Old School But Cool Video