1. Day 4 ELECTROMAGNETISM: The Magnetic Field of a Current Carrying Wire

2. Danish Physicist Hans Oersted made an accidental discovery in 1819
Danish Physicist Hans Oersted made an accidental discovery in He had a compass (with its needle pointing, as usual, to magnetic South) next to a wire. He connected a wire to the battery and found that the wire “induced” the compass needle to swing away from magnetic north. Thus, he found that:
When current flows through a wire, a magnetic field is created around the wire.

3. Let’s test this “Theory”
Compass ABOVE wire A B + -
wire loop

4. Let’s test this “Theory”
Compass BELOW wire A B + -
wire loop

5. Right-Hand Rule #2 (RHR-2)
The Magnetic Field Around a Current Carrying Wire
Right-Hand Rule #2 (RHR-2)

7. A B C

9. Magnetized Substance
Unmagnetized substance
What’s a SOLENOID?

10. OK, so RHR-2 gives us the direction of the magnetic field around a current-carrying wire. But since B is a vector, can we find the MAGNITUDE of the magnetic field?
m0 = the magnetic
permeability of free-space =
I = current (A)
d = distance from the center of
the wire.
Magnetic field strength, measured in Teslas (T)

11. What exactly is a Tesla again?
1T is REALLY big. So we often us prefixes like mT, mT, or nT.
The earth’s magnetic field is soooooo small that we often use a term called a GAUSS (G) to measure it.
1 G = 0.1mT (and the earth’s magnetic field is ~ G)

12. m0 = the magnetic
permeability of free-space =
I = current (A)
d = perpendicular distance
from the center of the wire.
This equation is only valid for VERY LONG, STRAIGHT wire. It will be derived in AP 1-2 using Calculus techniques.