The objective of this lab was to study the current flowing in the wire, the magnetic field
surrounding the wire, and the length of the wire immersed in the field. This lab was very similar
to past weeks because we had to set up circuit diagrams in series. This lab looks at the magnetic
force and Lorentz’s Law through three different Investigations. Magnetic force is the attraction
or repulsion that arises between electrically charged particles because of their motion. It is the
basic force responsible for such effects as the action of electric motors and the attraction of
magnets for iron. Lorentz force, the force exerted on a charged particle q moving with velocity v
through an electric E and magnetic field B.
In these Investigations we will be studying the effects of the current, effective wire length, and
strength of magnetic field on the magnetic force experienced by the wire. Investigation
1forcusses on the dependence of force on current. With no current flowing through the brass loop
the armature with the two counter weights must be balanced, with a current flowing through the
loop, a magnetic Lorentz force will act on the straight section of the brass wire because it is
inside the magnetic field. In Investigation 2 we will be focusing on the dependence of Force on
L’, the length of wire in the magnetic field. In this part of the lab we will vary the length of the
wire in the magnetic field with the current staying constant. The last Investigation is focused on
the dependence of force on the strength of the magnetic field B. In this Investigation we will vary
the strength of the magnet force by removing magnets but keeping the current and the wire
length constant.
Investigation 1
Setup & Procedure
Balance the armature by first rotating the adjustment wheel until it is located halfway along the
length of its threaded rod. Then push the rider to its leftmost position and record the lowest value
it will reach on the scale. Balance the armature with the balance adjustment wheel until the part
of the brass loop on which the rider sits is level and parallel to the top scale. Connect the power
supply and ammeters in series with the current balance apparatus. Make sure the ammeter is
connected in the high current setting. The settings should be on DC current and the range should
be 20 Amax. Turn the current control all the way down and the voltage control all the way up.
Turn the power supply on, turn the meter on, and slowly increase the current. Observe the
armature while increasing the current, if it moves downward reverse the current flow. Record the
length of the wire L inside the magnetic field. Align the edge of the magnetic assembly with the
value 50 mm. Slide the rider until reaching a major marking on the scale, increase the current
until the armature is back to being level. Record the current and the rider’s displacement form the
origin. Move the rider to its next major marking and level the armature by increasing the current.
Continue this process until the rider gets to the end of the scale or the current maxes out. Go back