Portable ladders approved for fire service use can support up to _____.

a. 750 lb
b. 450 lb
c. 300 lb
d. 600 lb


Answer: a. 750 lb

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Pure aluminum melts at ____ Fahrenheit.

A. 1200° B. 1500° C. 1800° D. 2200°

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The accompanying figure shows the parts of an open cornice. What is feature 4?

A. Rafter B. Wall plate C. Ventilator D. Siding

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What term is used to describe a battery's ability to conduct current.

A. ampere B. electrolyte C. voltage D. conductance

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An electromagnet is used to support a solid piece of steel, as shown in Example 18.9. A force of 10,000 N is required to support the weight. The cross-sectional area of the magnetic core (the fixed part) is 0.01 m2. The coil has 1,000 turns. Determine the minimum current that can keep the weight from falling for x = 1.0 mm. Assume negligible reluctance in steel and negligible fringing in the air gaps.


Example 18.9

An electromagnet is used to collect and support a solid piece of steel, as shown in Figure 18.38. Calculate the starting current required to lift the load and the holding current required to keep the load in place once it has been lifted and is attached to the magnet. Assume that the cross-sectional areas of the electromagnet, load (bar), and air gap are equal.
Assumptions:
Negligible reluctance for the steel parts and negligible fringing in the air gaps.

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