Automotive Electronics Practice Test

When discussing a signal showing the battery voltage on an analog oscilloscope, what does Technician A say the display will show?

1. One horizontal line above the zero line

2. A line sloping upward from zero to the battery voltage

3. A straight vertical line

4. Fluctuations around the zero line

The correct answer is: One horizontal line above the zero line

When monitoring the battery voltage on an analog oscilloscope, the correct interpretation of the display is that it will show a horizontal line above the zero line. This is because the battery voltage is a stable DC (direct current) signal, which does not vary significantly under normal conditions. A steady voltage from a battery, such as 12 volts for a standard automotive battery, would cause the oscilloscope to display a constant, flat line positioned at the corresponding voltage level on the vertical scale. This represents the fact that the voltage remains relatively constant over time, rather than fluctuating or transitioning, which would be characteristic of an AC (alternating current) signal or other variable signals. In contrast, a line sloping upward would suggest a change in voltage over time, which is not how a stationary battery would behave. A straight vertical line would indicate a sudden voltage spike, typically seen in transient events but not in steady-state battery operation. Fluctuations around the zero line would imply an oscillating signal or noise, which is not representative of a stable battery voltage. Thus, a horizontal line above the zero line accurately represents a constant battery voltage, confirming Technician A's assertion.