Concept explainers
BIO Footwear Safety
The American National Standards Institute (ANSI) specifies safety standards for a number of potential workplace hazards. For example, ANSI requires that footwear provide protection against the effects of compression from a static weight, impact from a dropped object, puncture from a sharp tool, and cuts from saws. In addition, to protect against the potentially lethal effects of an electrical shock, ANSI provides standards for the electrical resistance that a person and footwear must offer to the flow of
Specifically, regulation ANSI Z41-1999 states that the resistance of a person and his or her footwear must be tested with the circuit shown in Figure 21-63. In this circuit, the voltage supplied by the battery is ɛ = 50.0 V and the resistance in the circuit is R = 1.00 MΩ. Initially the circuit is open and no current flows. When a person touches the metal sphere attached to the battery, however, the circuit is closed and a small current flows through the person, the shoes, and back to the battery. The amount of current flowing through the person can be determined by using a voltmeter to measure the voltage drop V across the resistor R. To be safe, the current should not exceed 150 µF.
Notice that the experimental setup in Figure 21-63 is a dc circuit with two resistors in series—the resistance R and the resistance of the person and footwear, Rpf. It follows that the current in the circuit is I = ɛ/(R + Rpf). We also know that the current is I = V/R, where V is the reading of the voltmeter. These relationships can be combined to relate the voltage V to the resistance Rpf with the result shown in Figure 21-64. According to ANSI regulations, Type II footwear must give a resistance Rpf in the range of 0.1 × 107 Ω to 100 × 107 Ω.
Figure 21-63 Problems 103, 104, 105, and 106
104. • What is the resistance of the person and footwear when the voltmeter reads 3.70 V?
- A. 1.25 × 107 Ω
- B. 1.35 × 107 Ω
- C. 4.63 × 107 Ω
- D. 1.71 × 108 Ω
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