Solution: Since the total current is calculated to be 25.8 A, the circuit breaker will be tripped.
Sample problem: The toaster oven is rated at 1 kW; the microwave oven
is rated at 1.3 kW; the coffee maker is rated 800 W. If all three appliances are
operated simultaneously, will a circuit breaker rated at 20 A be tripped?
Solution: Since the total current is calculated to be 25.8 A, the circuit
breaker will be tripped.
Sample problem: A good car battery is being used to jump start a car
with a weak battery. The good battery has an emf of 12.5 V and an internal
resistance of 0.02 Ω. The weak battery has an emf of 10.1 V and an internal
resistance of 0.10 Ω. Each copper jumper cable is 3 m long and 0.5 cm in
diameter. Treat the starter as a simple resistor with a resistance of 0.15 Ω.
Determine the current through the starter with and without the good battery.
Solution: The negative value of I2 implies that the stronger
battery is pushing current back into the weaker battery. The terminal voltage of
the weaker battery is thus 10.1+6.2*0.10=10.7 V, which means that it is being
charged.
Sample problem: What is the current through the switch right after the
switch is closed? What is the current a long time after the switch is closed?
What is the voltage and charge on the fully charged capacitor? After the switch
is opened, how long does it take for the capacitor to discharge to 5% of its
full charge?
Solution: Right after the switch is closed, the capacitor is not charged
and therefore acts like a piece of wire (with zero resistance). This implies
that the upper two resistors are in parallel, and this combination is in series
with the lower two resistors, which are also in parallel. After a long time, the
capacitor is fully charged and therefore acts like an open switch. This implies
that the left two resistors are in series, and this combination is in parallel
to the in-series combination of the right two resistors.
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