Download Solutions to Period 14 Exercises

Solutions to Period 14 Exercises
E.1 Household wiring (120 volts) is usually
divided into several fused circuits, each
with a fuse or circuit breaker that blows
when the current exceeds 15 amps. If you
operate a 250 watt TV, a 1000 watt iron,
and two 100 watt bulbs all at once from
one circuit, how much power is being used?
a) Less than 1000 watts
b) 1350 watts
c)
1450 watts
d) More than 2000 watts
Total Power = sum of the power drawn by
the appliances
= 250 W + 1,000 W + 2 (100 W) = 1,450 W
E.1 = c
14-Ex 1
E.2 In question E.1, what is the total current
being drawn by these appliances from the
120 volt line? Will the 15 amp fuse blow?
a) Less than 10 amps; fuse does not blow.
b) About 12 amps; fuse does not blow.
c)
About 13 amps; fuse does not blow.
d) More than 18 amps; fuse blows.
Solve P = I V for I:
I = P = 1450 W = 12 A
V
120 V
E.2 = b
14-Ex 2
E.3 You are standing in wet shoes on a damp
concrete floor that has a resistance of
10,000 ohms. If you touch the hot side of a
120 volt line with wet hands, about how
much current could flow through you?
(Hint: approximate the resistance
connected across 120 volts by the sum of
10,000 ohms and your “wet hands” body
resistance of 5,000 ohms.)
a) 0.0008 amps
b) 0.008 amps
c)
0.08 amps
d) 0.8 amps
Solve V = I R for I:
I = V = 120 V =
R
15,000 Ω
0.008 amps
E.3 = b
E.4 Is the current in E.3 dangerous? What
effect is it likely to have on your body?
This amount of current is painful and could
paralyze some muscles.
14-Ex 3&4
E.5 A current at a voltage of 120 V flows into a
transformer. A 10 amp current at a voltage
of 240 V flows out of the transformer. How
much current flows into the transformer?
Is this a step up or a step down
transformer?
a) 5 amps; step up transformer
b) 5 amps, step down transformer
c)
20 amps; step up transformer
d) 20 amps; step down transformer
e) 40 amps; step down transformer
Solve Ip x Vp = Is x Vs for Ip
Ip = Is x Vs = 10 A x 240 V = 20 A
Vp
120 V
The voltage out is greater than the voltage
in. Therefore, the transformer steps up the
voltage.
E.5 = c
14-Ex 5
Solutions to Period 14 Exercises
E.1 = c
E.2 = b
E.3 = b
E.4 = This amount of current is painful and
could paralyze some muscles.
E.5 = c
14-Ans