Which device measures the opposition to current flow when a known voltage is applied?

The device that measures the opposition to current flow when a known voltage is applied is indeed an impedance meter. An impedance meter is specifically designed to assess the impedance, which is a complex measure that accounts for both resistance and reactance in an electrical circuit. It applies a known voltage to a circuit and measures the resultant current flow to calculate the impedance using Ohm's law.

In contrast, an oscilloscope is primarily used for visualizing voltage waveforms over time and does not measure impedance directly. A multimeter can measure voltage, current, and resistance but may not provide a specific measurement of impedance unless it has an impedance function. An analog voltmeter measures just the voltage across two points in a circuit but does not provide information on the opposition to current flow. Thus, the impedance meter is the most appropriate choice for measuring the opposition to current flow in this context.