Cathode Ray Oscilloscope Questions and Answers

Answer: C

A voltage rising linearly with time sweeps the spot across the screen at constant speed, so horizontal distance represents time. The rapid fall at the end of each sweep returns the spot to the left, and the whole waveform is a sawtooth.

Answer: D

Correct answer: little of the sweep time is wasted

The retrace carries no information, so any time spent on it is time the trace is not displaying the signal. Making the flyback a small fraction of the period keeps the duty cycle high and the trace bright and continuous. The beam is blanked during it in any case, so phosphor damage and trigger discrimination are not the concern.

Answer: A

Correct answer: applying a negative pulse to the control grid

The control grid sits between cathode and anode and its potential governs how many electrons pass, so driving it strongly negative cuts the beam off entirely. A blanking pulse derived from the time base is applied there during the flyback, so the returning spot leaves no trace. Removing the accelerating voltage would be far too slow and would defocus everything.

Answer: B

Correct answer: each sweep starts at the same point on the waveform

A stationary display requires successive sweeps to be superimposed, and that requires each to begin at the same point in the signal’s cycle. The trigger circuit does this by starting the sweep when the signal crosses a chosen level in a chosen direction. It does not require the sweep frequency to equal the signal frequency - only that the start points coincide.

Answer: C

Each sweep is initiated by the signal crossing a chosen level in a chosen direction, so the display is stable without the operator matching frequencies by hand. It also allows a single non-repetitive event to be captured, which a free-running base cannot do.

Answer: D

The sweep begins when the input crosses that voltage, so moving the control moves the starting point along the waveform and shifts the displayed pattern horizontally. Setting it outside the signal range means no trigger and no display at all.

Answer: A

Selecting the negative slope makes the sweep begin as the waveform falls through the trigger level instead of rising through it, which shifts the display by half a cycle on a symmetrical wave and matters greatly on a pulse train.

Answer: B

A timer starts a sweep if nothing has triggered for a while, so a baseline is always visible and the operator is not left with a blank screen while hunting for the level. Normal mode shows nothing until a genuine trigger occurs.

Answer: C

The trigger circuit and the sweep generator take a little time to start, so without a delay the first part of the very edge that triggered the sweep would already have passed. Delaying the signal by rather more than that lets the edge itself be displayed.

Answer: D

The convention is the three decibel point, where the amplitude ratio is one over root two. A sinusoid at the bandwidth frequency is therefore displayed about thirty per cent small, which is why amplitude measurements are made well below it.