- Electricity and Magnetism^85
Determine the current^12 required to
fuse the second wire, assuming that the
amount of heat dissipated to the ambient
per second obeys the law Q=kS (T — Tam),
where S is the cross-sectional area
of the wire, T is its temperature, T.m is
the temperature of the ambient away from
the wire, and k is the proportionality factor
which is the same for the two wires.
3.32. The key K in circuit diagram shown
in Fig. 90 can be either in position 1 or 2.IFig. 90The circuit includes two d.c. sources, two
resistors, and an ammeter. The emf of one
source is el and of the other is unknown.
The internal resistance of the sources
should be taken as zero. The resistance of the
resistors is also unknown. One of the re-
sistors has a varying resistance chosen in
such a way that the current through the am-
meter is the same for both positions of the
key. The current is measured and is found
to be equal to I.
Determine the resistance denoted by 14
in the diagram.