Explanation: Both hot wire and thermocouple ammeters are effective for measuring RF currents because their operation relies on the *heating effect* of current (Joule heating, P = I²R). Radio frequency (RF) currents, like any electrical current, generate heat when flowing through a resistive element. These meters convert this heat into a measurable indication. * A **hot wire ammeter** directly measures the physical expansion of a wire caused by the heat generated by the current passing through it. This expansion is proportional to the square of the current. * A **thermocouple ammeter** uses the heat generated by the RF current in a resistive element (heater) to raise the temperature of a thermocouple junction. The thermocouple then produces a small DC voltage proportional to this temperature, which is measured by a sensitive DC voltmeter. Since both methods depend on the total heat generated by the current, rather than its instantaneous direction or magnetic field (which would be problematic at high RF frequencies), they are well-suited for measuring RF currents across a broad frequency range.