Passage V

A material is a superconductor (its electrical resistance, R, is zero) if its temperature, T, is lower than its critical temperature, Tc.

Students measured R and T for both a sample of Material X and a sample of Material Y while, each sample was cooled. They used an ohmmeter to measure R (in ohms) and a thermocouple to measure T. The thermocouple displayed the result of each measurement of T as a voltage (in millivolts, mV). Accordingly, the students plotted R versus voltage (see Figure 1). To convert voltage in mV to T in kelvins (K), they used Table 1.

Figure and table adapted from "instruction Manual for Superconductor Demonstrations." @1992 by Colorado Superconductor, Inc.

25. Based on Figure 1 and Table 1, the range of temperatures over which Material X is a superconductor is closest to which of the following?

Answer and Explanation

Your Answer is

Correct Answer is C

Explanation

The definition given in the first paragraph of the article for a Superconductor superconductor is regarded as having a resistance of 0.

Refer to figure 1. When the voltage is greater than or equal to 6 mV, the resistance of X is 0. Go back to table 1 and find the value 6.01 mV closest to 6mV. The corresponding temperature is 87 K. So as long as the temperature is greater than or equal to 87 K