Victory for the ACT Student Text 15e

334 • S CIENCE

Passage III Using electrical circuits, three experiments were performed to investigate the relationship between voltage (in volts), resistance (in ohms), and current (in amperes). Each experiment was set up with the following circuit design: Experiment 1 Using a 6-volt battery and two 1,000-ohm resistors ( 1 R and 2 R ), the measured voltages between points 1 and 2 and between points 2 and 3 were 3 volts each. Judging from the results in Experiment 1 and Experiment 2, if the battery voltage were changed to 1.5 volts and both resistors were 1,000 volts, what voltage would be expected between point 1 and point 2? A. 0.75 volts B. 1.5 volts C. 3.0 volts D. 6.0 volts 10. According to the diagram, which atmospheric layer shows the greatest decrease in temperature per unit increase in altitude? F. thermosphere G. mesosphere H. stratosphere J. troposphere 11.

Experiment 2 Using a 12-volt battery and the same resistors as in Experiment 1, the measured voltages between points 1 and 2 and between points 2 and 3 were 6 volts each. Experiment 3 Using the battery from Experiment 1 and a 1,000-ohm resistor and a 2,000-ohm resistor, the measured voltages between points 1 and 2 and between points 2 and 3 were 4 volts and 2 volts, respectively. EXPLANATIONS 10. (J) Science/Interpretation of Data/ Analysis According to the diagram, the temperature decreases with increasing altitude in the mesosphere and troposphere only, so eliminate (F) and (H). To choose between (G) and (J), compare the slopes of the data lines. The temperature decreases by about 120°C per an increase of 20 kilometers in the troposphere, while the temperatures decreases by about 100°C per 35 kilometers in the mesosphere. So the greatest decrease in temperatures per unit increase in altitude happens in the troposphere, (J).

The Cambridge Edge For speed and accuracy, it is helpful to draw diagrams of Experiments 1, 2, and 3. This method helps you quickly answer questions that ask you to manipulate parts of each experiment, such as questions 11, 12, and 15. Also, any questions about experimental set-up can be easily tackled using this method.

EXPLANATIONS

11. (A) 6FLHQFH 6FLHQWLÀF ,QYHVWLJDWLRQ $SSOL- cation The experiments show that the measured voltages are one-half of the battery volt- age.