Oscilloscope fundamentals (CRT-based): What primary quantities does a cathode-ray oscilloscope (CRO/CRT oscilloscope) visually display on its screen for a typical time-domain measurement? Select the best pair that reflects what is directly observed and measured from the graticule and timebase.

Introduction:An analog CRT oscilloscope (often called a CRO) is a time-domain instrument. It plots a voltage as a function of time using a vertical deflection system (voltage) and a horizontal timebase (time). From this plot, we directly read amplitude and time-related quantities such as period; frequency is then inferred as the reciprocal of the measured period.

Given Data / Assumptions:

• Standard time-domain setup with channel input driving vertical plates.
• Horizontal sweep set by the timebase (time/div).
• Graticule used to measure vertical and horizontal distances.

Concept / Approach:

The oscilloscope presents instantaneous voltage on the vertical axis versus time on the horizontal axis. By counting horizontal divisions for one complete cycle and multiplying by the time/div setting, we directly obtain the period. Amplitude is read vertically in volts/div. Frequency is a derived value: f = 1 / T, not a directly displayed quantity.

Step-by-Step Solution:

Verification / Alternative check:

Any CRO user manual describes measurements of amplitude and period directly from the screen. Built-in cursors (in DSOs) still operate on time and voltage axes, reinforcing that these are the directly displayed axes.

Why Other Options Are Wrong:

• current and frequency: Current is not directly displayed unless converted to voltage via a shunt; frequency is derived.
• rms voltage and current: RMS requires calculation; the scope shows instantaneous waveform.
• frequency and voltage: Frequency is computed from period; period is the directly measured time quantity.
• phase angle and impedance: These require multi-channel or additional computations; not direct screen axes.

Common Pitfalls:

• Confusing what is directly displayed (time and voltage) with values derived after calculation (frequency, RMS).
• Assuming current is shown without a transducer; scopes measure voltage.

Final Answer:

voltage and period