Cathode Ray Oscilloscope Questions and Answers

Answer: C

Rounded corners mean the probe passes the high frequencies less readily than the low, that is under compensation. The trimmer is adjusted while watching the calibrator square wave until the top of the wave is flat and the corners square.

Answer: D

A sampling oscilloscope needs the waveform to repeat, since it builds the picture from many cycles, and a free-running base would almost certainly be elsewhere when the event happened. Only a storage instrument triggered by the event itself will capture it.

Answer: A

An external graticule sits a few millimetres in front of the phosphor, so the reading changes as the observer's eye moves. Marking it on the inner face puts scale and trace in the same plane and removes the error entirely.

Answer: B

It is a square wave of accurately known amplitude and, usually, a round frequency. Displaying it confirms the volts per division calibration and, since it has fast edges, provides the waveform against which a probe trimmer is set.

Answer: C

The analogue instrument writes every sweep to the phosphor, so an infrequent event appears as a faint trace against the bright envelope, and the relative brightness itself conveys how often it happens. A digital instrument may miss it entirely between acquisitions unless a peak detect mode is used.

Answer: D

It is connected to the control grid circuit, so an external waveform can brighten or blank the beam. Marking a trace with timing pips from a standard frequency source is the classic use, and it also serves for intensity modulation in raster displays.

Answer: A

Plotting one quantity against another is exactly what X-Y mode provides, the horizontal plates being driven by the second signal instead of by the sawtooth. A current sensing resistor converts the current into the voltage the vertical channel needs.

Answer: B

Deflection coils are inductive and their impedance rises with frequency, so driving them at megahertz rates is impractical. Plates present a small capacitance and can be driven to hundreds of megahertz, which is what an oscilloscope needs above all else.

Answer: C

The sweep itself is unchanged but the horizontal amplifier gain is raised tenfold, so a tenth of the sweep fills the screen. Any part of it can then be examined by shifting with the horizontal position control, at the cost of a dimmer and less accurate trace.

Answer: D

At high frequencies an unterminated cable reflects, and the reflections appear on the screen as ringing that has nothing to do with the signal. Matching the cable in its characteristic impedance absorbs the wave, at the cost of loading the source with fifty ohms.