Chapter 20: Selected Exercises

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Table of Contents

  #2

#6

#10

#16

#20

#22

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2.  An old truck battery produced 24 Volts.  If each cell produced two Volts, how many cells did the battery have?

This is like having some unknown number N batteries in series.



6.  If a curling iron has a resistance of 800 Ohms when hot, what current does it require?  (As discussed in class, we must assume a standard U.S. household voltage of 120 Volts.)

We use Ohm's law to solve this exercise.



10.  Two 1.5 Volt batteries are connected in parallel to a 6 Ohm resistor.  How much current does each battery supply?

Here too, we use Ohm's law to solve our problem.



16.  If a clock draws a maximum current of 5 mA, what is its maximum power consumption?  (Household voltage of 120 Volts must be assumed.)

Noting that mA is the abbreviation for milli-Amps, that is 1/1000 Amps, we use the relation that power is the current times the voltage to find the maximum power.



20.  If a 40 Watt bulb is left on continuously in a secluded hallway, how much energy is used each month?

Recall that power is energy divided by time.  Then,



22.  A 1500-Watt heater for a sauna requires 45 minutes to heat the sauna to 190 degrees Fahrenheit.  What does this cost if electricity costs 8 cents per kW-hr?

The method used in this problem, coupled with the rate you pay per kilowatt-hour, could help you keep a handle on your electric bill!