Phy 132 - Assignment 5
A. Whether terms for resistors are positive or negative comes from
remembering that current flows from higher to lower voltage. (+ to -.)
B. 1.
2.
C.
D. 1. 25 W has the higher resistance. Power = V2/R, so with the same voltage
on both, more ohms means less watts.
100 W carries more current, by V = IR.
(In words instead of equations, more current (more electrons per second) is
needed through the 100 W bulb to deliver the greater power (greater energy per
second). The 100 W bulb must have less resistance to let that greater current
through.)
2.
E. 1. For a current to flow, it needs someplace to flow to. The bird, touching
nothing but the wire, is not part of a complete circuit. The child is in contact
with the ground; if the kite’s string was damp enough to be conducting – zap.
2. Every term in the summation should be a voltage. The I2 term has amps for
its unit, not volts.
3.
F. 1. When no current is flowing through the battery. (The potential difference
between a battery’s terminals is E – Ir, where r is the internal resistance.)
2. Knock the person’s hand from the wire using some insulating object. (A
meterstick if it isn't metal, or a shoe if it isn't damp, or …) Do not touch the
person directly unless you are absolutely sure that you are not grounded.
3.