1. STARTER
Which way does the current point in this wire?

2. Calculating the Magnetic Field of a Current-Carrying Wire
A long, straight wire
A current loop
A coil or solenoid

3. A Long, Straight Wire
mo = 4p x 10-7

4. Example A long, straight wire carries 50A of current. What is
the value of the magnetic field 5mm above the wire?
Also, indicate the direction.
B = moI/2pr = (4p x 10-7)(50)/(2p)(5 x 10-3) =
(2 x 10-7 )(50) /(5 x 10-3) = .20T

5. A Current Loop
mo = 4p x 10-7
B= 𝜇 𝑜 I/2R
R = loop radius

6. Example A loop of current, radius =5.00cm, carries 50Amps.
What is the value of the magnetic field at the loop’s center?
B = moI/2R = (4p x 10-7)(50)/(2)(5 x 10-2) =
= x 10-4 T

7. A Coil B= 𝜇 𝑜 IN/L N = number of turns I = current in amps
L = length of coil (m)
B= 𝜇 𝑜 IN/L
mo = 4p x 10-7

8. Example A coil has 5000 turns and is 5cm long. If 5A of
current run through the coil, what is the value of the
magnetic field inside the coil?
B = moIN/L = (4p x 10-7)(5)(5000)/(5 x 10-2) =
= .628T

9. The Force on a Moving Charge in a Magnetic Field
q = charge in Coulombs
v = velocity in m/s
B = magnitude of the B- field
q = angle between B and v
F = qvBsinq

10. Direction of the Force on a Moving Charge in a B-Field
Point the fingers of your right hand in the direction of the velocity.
Rotate your wrist until you can fold your fingers 90 degrees and point in
the direction of B.
Your thumb points in the direction of the force.

11. Example F = qvBsinq = .002(100)2sin90 = .400N , OUT
A 2mC charge moving at 100m/s passes through a 2T B-field at right angles as shown. What force does it feel? What is the direction?
F = qvBsinq = .002(100)2sin90
= .400N , OUT

12. The Force on a Current-Carrying Wire in a Magnetic Field
i = current in the wire in amps
L = length of the wire
B = magnitude of the B- field
q = angle between B and v
F = BiLsinq

13. Direction of the Force on a Current-Carrying Wire in a B-Field
Point the fingers of your right hand in the direction of the current (i).
Rotate your wrist until you can fold your fingers 90 degrees and point in
the direction of B. Your thumb points in the direction of the force.

14. Example F = BiLsinq = 2(10)2sin90 = 40.0N , IN
A 2m long wire with a current of 10A is in a 2T B-field at right angles as shown. What force does it feel? What is the direction?
F = BiLsinq = 2(10)2sin90
= 40.0N , IN