FCC Exam Question: 3-76L1

What is used to decrease circuit loading when using an oscilloscope?

A. Dual input amplifiers.
B. 10:1 divider probe.
C. Inductive probe.
D. Resistive probe.
Correct Answer: B

Explanation: An oscilloscope's input has a characteristic impedance, typically 1 MΩ in parallel with some picofarads of capacitance. Connecting this directly to a high-impedance circuit can "load" it, meaning it draws significant current or adds capacitance, altering the circuit's normal operation. A **10:1 divider probe** contains a series resistor (e.g., 9 MΩ) and a compensating capacitor. When connected to the oscilloscope's 1 MΩ input, this effectively increases the *overall* input impedance seen by the circuit to 10 MΩ while also reducing the effective input capacitance. A higher input impedance draws less current from the circuit, thereby significantly decreasing the loading effect and allowing for more accurate measurements without disturbing the circuit under test. Dual input amplifiers (A) allow viewing multiple signals but don't inherently reduce loading. Inductive (C) and resistive (D) probes are general terms; the specific 10:1 divider probe is designed for impedance matching and load reduction.

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Includes Elements 1, 3, 6, 7R, 8, and 9.