# Tag Info

Accepted

### How does the echo of a radio wave from Venus depend on the rotation speed and direction of the planet?

There is a Doppler signal. The frequency of the reflected wave is changed by the reflector moving, and that shift is measured to get the velocity, usually by mixing with a wave of known frequency or ...
• 1,531
1 vote

### Why do we even need RF cavities to accelerate particles?

It is important to note that the electric scalar potential $\phi$, expressed in unit of volts, is a single valued function. If there is a downhill that accelerates the positive particle, there is ...
• 532

### Why do we even need RF cavities to accelerate particles?

The reason they'd decelerate is that the space beyond the positive electrode is, in a practical experiment, surrounded by "grounded" stuff (beam pipe, etc.). So, there's effectively a second ...
• 5,430
Accepted

### Why do we even need RF cavities to accelerate particles?

The key limitation for using a constant electric field (i.e. DC acceleration) is that all materials have an intrinsic breakdown electric field where insulators stop being insulators (true even for air ...
• 6,020