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Chapter 21: Q18CQ (page 772)

Semi-tractor trucks use four large\({\rm{12 - V}}\) batteries. The starter system requires \({\rm{24}}\;{\rm{V}}\), while normal operation of the truck’s other electrical components utilizes \({\rm{12}}\;{\rm{V}}\). How could the four batteries be connected to produce \({\rm{24}}\;{\rm{V}}\)? To produce \({\rm{12}}\;{\rm{V}}\)? Why is \({\rm{24}}\;{\rm{V}}\) better than \({\rm{12}}\;{\rm{V}}\) for starting the truck’s engine (a very heavy load)?

Short Answer

Expert verified

A larger voltage gives more power. Thus, \({\rm{24\;V}}\) battery is used in the starter system.

Step by step solution

01

Relation between power and voltage

Power and voltage are proportional to each other if the current is kept constant

02

Step 2: Connection of batteries to get \({\rm{24V}}\)

For creating a voltage \({\rm{12\;V}}\), connect two batteries in parallel, whereas connect two in series to generate a voltage \({\rm{24\;V}}\). It is better to put \({\rm{24\;V}}\)for starting a heavy load because a lower voltage will not be able to produce the required power as the applied resistance will be higher.

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Most popular questions from this chapter

Suppose you measure the terminal voltage of an1.585-V alkaline cell having an internal resistance of0.100Ωby placing arole="math" localid="1656394302991" 1.00-kΩvoltmeter across its terminals. (See Figure 21.54.) (a) What current flows? (b) Find the terminal voltage. (c) To see how close the measured terminal voltage is to the emf, calculate their ratio.

Specify the points to which you could connect a voltmeter to measure the following potential differences in Figure \(21.49\): (a) the potential difference of the voltage source; (b) the potential difference across \({R_1}\) ; (c) across \({R_2}\) ; (d) across \({R_3}\) ; (e) across \({R_2}\) and \({R_3}\) . Note that there may be more than one answer to each part.

Two different 12-Vautomobile batteries on a store shelf are rated at 600and 850“cold cranking amps.” Which has the smallest internal resistance?

Why should you not connect an ammeter directly across a voltage source as shown in Figure21.48?(Note that script Ein the figure stands for emf.)

Figure 21.55 shows how a bleeder resistor is used to discharge a capacitor after an electronic device is shut off, allowing a person to work on the electronics with less risk of shock. (a) What is the time constant? (b) How long will it take to reduce the voltage on the capacitor to 0.250%(5% of 5%) of its full value once discharge begins? (c) If the capacitor is charged to a voltage V0 through a 100-Ω resistance, calculate the time it takes to rise to 0.865V0 (This is about two-time constants.)
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