Which property of a tube is the ratio of the change in plate voltage to the change in grid voltage needed to achieve a corresponding change in plate current?

The property described in the question pertains to the relationship between changes in plate voltage, grid voltage, and plate current within a tube (or vacuum tube). The amplification factor is defined as the ratio of the change in plate voltage to the change in grid voltage that is necessary to produce a corresponding change in plate current. This concept is fundamental in understanding how effectively a vacuum tube can amplify signals, as it reflects the tube's capability to control the current flow based on varying input voltages.

In the context of tube operation, the amplification factor is an essential parameter that helps to determine how much output signal (plate current) can be influenced by input signal changes (grid voltage). A higher amplification factor indicates superior amplification capability, which is why this property is often discussed in the context of tube performance.

Other options like transconductance, plate resistance, and load impedance pertain to different aspects of tube operation and behavior. Transconductance measures how effectively the tube converts a change in grid voltage to a change in plate current, while plate resistance refers to the resistance seen by the plate circuit of the tube. Load impedance relates to the impedance at which the output of the tube operates but does not directly define the relationship between plate voltage, grid voltage, and plate current in