1. Magnetic Field due to a Current-Carrying Wire
Physics
Mrs. Coyle

2. A Current-Carrying Wire Causes a Magnetic Field Around it.

3. Hans Christian Oersted, 1820

4. Right Hand Curl Rule

5. Magnetic Fields of Long Current-Carrying Wires
B = mo I
2p r
I = current through the wire (Amps)
r = distance from the wire (m)
mo = permeability of free space
= 4p x 10-7 T m / A
B = magnetic field strength (Tesla) I

6. Example 1
What is the magnitude of the magnetic field created by a 0.25A current at a distance of 50cm from the wire?
Answer: 1x10-7 Tesla

7. Magnetic Field of a Current Carrying Wire

8. Magnetic Field in the Center of a Current-Carrying Loop (Ring) B = mo I 2 r

9. Note
The overall shape of the magnetic field of the circular loop is similar to the magnetic field of a bar magnet.

10. Magnetic Field at Center of a Solenoid B = mo NI L
N: Number of turns
L: Length
n=N/L
 L 

11. Force of Attraction Between Two Long Current-Carrying Wires
F= mo I1 I2 L
2p d
d : distance between wires
I : current
L: length of wire

12. Note
If the wires have currents in opposite directions, the wires repel each other.

13. Example 2
What is the force of attraction felt by two 4m long current-carrying wires carrying currents of 2A and 3A, that are 60cm from each other?
Answer: 8x10-6 N