Question

dc versus ac problem. suppose your dc power supply is set to 15 v and the vertical setting on the oscilloscope is at 5 v/div. how many divisions will the trace deflect if you connect the output of the power supply to the scope with the a input switch set on dc? how many divisions if the switch is on ac? please write your answer with integer values.

Answer 1

• DC: 3 divisions
• AC: 0 divisions

Step-by-step explanation:

You want to know the deflection of the trace on an oscilloscope set to 5 V/div when it is connected to a 15 V DC power supply, both when the 'scope is set to DC input coupling, and when it is set to AC input coupling.

DC

When the input coupling is DC, the input voltage difference from ground (or the reference level) will deflect the oscilloscope trace according to its sensitivity setting.

15 V/(5 V/div) = 3 div

The trace will be deflected 3 divisions.

AC

The oscilloscope will register any AC content that is within its bandwidth when the input coupling is set to AC. A good DC power supply will have no AC content, so the deflection of the trace will be zero, 0 divisions.

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Additional comment

The trace may be deflected briefly, then settle back to zero, when a DC power supply is connected to a 'scope set for AC input. The act of connecting the supply provides a step-function input to the 'scope, which has an AC content. The duration of the deflection will depend on the time constant of the input circuit.