Magnetism and Electricity
Magnetic field about a wire carrying a current
Hans Christian Oersted, a danish physicist conducted the following experiment in 1820. Oersted experiment -LeifiPhysik
Another experiment that followed from that:
Around a wire with a current
The right hand can be used to determine the magnetic field about the wire. The thumb points in direction of the conventional current + –> -.
In a solenoid (coil)
This leads to the effect of a current through a coil of wire (solenoid) …
The fingers curl over in direction of the conventional current. The thumb points in direction of the North pole of the solenoid.
Lorentz force
Question: What happens to the direction of the force after the coil makes a 180° rotation?
Right-hand (Mr Williams: “Why use the other hand?”)
After some contortions to get the hand into the correct position.
Comparing the right hand with the left hand.
- Thumb - conventional current + –> -
- Index finger - magnetic field N –> S
- Middle finger - direction of force
$F_L$
Flemming’s left hand rule for the same phenomena
- Thumb - Force
- Index finger - magnetic field dd
- Middle finger - direction of conventional current + –> -
Calculations
magnetic flux - magnetische Flussdichte
Experiments show that the force on a conductor in a magnetic field is directily proportional to:
- the magnetic flux density, B
- the current I, and
- the length l of the conductor in the field
$F = B \cdot I \cdot l$
or
$B = \frac{F_L}{I \cdot l}$ where $F_L$ is the German notation for the Lorentz force.
wire not perpendicular to the magnetic field
If the wire is not perpendicular to the magnetic field, but at an angle $\theta$ say, then the only the perpendicular component is considered and calculated as follows.
$F = B \cdot I \cdot l \cdot \sin{\theta}$
magnetic flux inside a long, influence of the material - magnetische Flussdichte im Inneren einer langen Spule, Einfluss von Materie auf die Flussdichte
$B = \mu_0 \cdot \mu_r \frac{N \cdot I}{l}$
magnetic force on a moving charge
Lorentz force - LORENTZkraft $F_L = Q \cdot v \cdot B$
- Q - charge (C)
- B - flux density (T)
- v - velocity (
$\frac{m}{s}$)