Understanding CRO Measurement Capabilities

A Cathode Ray Oscilloscope (CRO) is primarily designed to display and measure electrical signals, especially voltage as a function of time.

• Voltage: CROs directly measure voltage amplitudes and variations.
• Voltage Ripple: This is a type of voltage fluctuation, which is clearly visible and measurable on a CRO screen.
• Current: While not measured directly, current can be inferred. By placing a known resistor ($R$) in series and measuring the voltage drop ($V$) across it, current ($I$) can be calculated using Ohm's Law: $I = V/R$.

Limitations of CRO Measurement

Resistance is an electrical property representing opposition to current flow. It's a static characteristic of a component or circuit, not a time-varying signal.

A CRO displays voltage waveforms over time. It cannot inherently measure a property like resistance, which requires a different measurement principle (like applying a known voltage/current and measuring the other, typically done by an ohmmeter).

Conclusion

Therefore, resistance is the property that cannot be directly measured using a CRO device.