Magnetic Balance.
The circuit shown in Fig. E27.42
is used to make a magnetic balance
to weigh objects. The mass
to be measured is hung from
the center of the bar that is in a
uniform magnetic field of 1.50 T,
directed into the plane of the figure.
The battery voltage can be
adjusted to vary the current in the
circuit. The horizontal bar is
60.0 cm long and is made of extremely light-weight material. It is
connected to the battery by thin vertical wires that can support no
appreciable tension; all the weight of the suspended mass is supported
by the magnetic force on the bar. A resistor with
is in series with the bar; the resistance of the rest of the circuit is much
less than this. (a) Which point, or should be the positive terminal
of the battery? (b) If the maximum terminal voltage of the battery is
175 V, what is the greatest mass that this instrument can measure?