De La Salle University SHS-ABM 12 EXPERIMENT #4 OHM’S LAW.

EXPERIMENT #4: OHM’S LAW
OBJECTIVES
1. To become familiar with Ohm’s law.
2. To study the sign convention as regard voltages and currents.
PROBLEMS
1. Why can’t Ohm’s law be described in terms of “constant proportionality”?
 Generally, if we take the formula of Ohm’s Law as the basis for the meaning of
its concept, then it cannot be considered as “constant proportionality.” It is
because voltage is directly proportional with the product of current and
resistance (V=IR). However, resistance is inversely proportional with current
(R=1/I), and current is inversely proportional with resistance (I=1/R). With
such, the proportionality of the three variables is not constant.
2. Why does the E/I ratio of an electric circuit indicate its ability to oppose
electric current rather than its ability to permit current flow?
 The equation for Ohm’s Law is V=IR, where V is the voltage, I is the
current, and R is the resistance. By formula derivation, it can be
interpreted as R=V/I, which says voltage divided by current is equal to
the resistance. Since resistance, R is the ability of a conductor to resist,
block or prevent current and/or voltage, it can be inferred that the
equation R=V/I indicates the ability of a circuit to resist or oppose the
current.
3. An electric fuse consists of a small strip of wire with a low melting
temperature. The current in the protected circuit flows through this strip.
Which will have a greater resistance, a 10A fuse or a 20A fuse? Explain.
 Based on the equation of wire resistance with respect to its area, as the
area increases, the resistance decreases. With increasing area, the current
also increases. Therefore, 20A fuse has less resistance than 10A fuse,
because the area of the wire in 20A fuse is greater than the area of the wire
in 10A fuse. To conclude, 20A fuse allows more flow of current than 10A
fuse.
4. What is meant by a mil-foot section of wire?
 A mil-foot is a section of wire which is equal to one-foot long and one mil in
diameter. It is the unit of measurement of resistivity in ohms per mil-foot. For
wires, it can also be called circular mil-foot. Its unit of conversion is about
0.0377 cubic inches (in3) or 0.6178 cubic centimeters (cm3).