The GATE Grind

GATE 2025 IN – Question 26

Measurements · Time frequency and instruments · 1 mark · Multiple choice

An oscilloscope has an input resistance of 1 MΩ. A 10X passive attenuating probe is connected to it to increase the input voltage range as well as the effective input resistance. The effective input resistance, in MΩ, seen into the probe tip is

  1. 0.9
  2. 9.1
  3. 10
  4. 11

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Show answer and explanation

Correct answer: (C) 10

Explanation

For tenfold voltage attenuation into 1 MΩ, the probe adds a 9 MΩ series resistor.

The source at the tip therefore sees 9+1=**10 MΩ, C** at DC.

Probe capacitive compensation preserves the ratio over frequency.