The rise time of an oscilloscope and its bandwidth are related approximately by the product
Answer: A
For a response approximating a single time constant, the rise time in seconds multiplied by the bandwidth in hertz is about 0.35. A hundred megahertz instrument therefore has a rise time of about 3.5 nanoseconds, which limits the edges it can resolve.
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A 10:1 attenuator probe is used with an oscilloscope chiefly to
Answer: B
The series resistance in the probe raises the input impedance tenfold and reduces the effective input capacitance, so a high impedance circuit is disturbed far less. The price is a tenfold loss of signal, which must be allowed for in reading the screen.
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The small adjustable capacitor in a 10:1 probe is set so that
Answer: C
The divider must attenuate by ten for direct voltage and for the fastest edges alike, which requires the capacitive division to match the resistive one. A square wave of known shape is displayed and the trimmer set until the top of the wave is flat.
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An over-compensated oscilloscope probe displays a square wave with
Answer: D
Too much capacitance in the probe passes the high frequencies too readily, so the edges are exaggerated and each transition overshoots before settling. Under-compensation gives the opposite, a rounded and slowly rising top.
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The input coupling switch of an oscilloscope set to AC inserts
Answer: A
The capacitor blocks any steady component, so a small alternating signal riding on a large direct voltage can be examined at high sensitivity. The penalty is that the true zero level is lost and low frequency square waves are distorted.
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Examining a small ripple superimposed on a 300 V direct supply is best done with the input coupling set to
Answer: B
On direct coupling the trace would be driven far off the screen at any sensitivity able to show a few volts of ripple. Blocking the steady component brings the ripple to the centre of the screen where it can be measured at high sensitivity.
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The X-Y mode of an oscilloscope disconnects
Answer: C
The horizontal plates are then driven by a second input signal instead of by the sawtooth, so the display becomes a plot of one signal against the other. Lissajous figures, hysteresis loops and device characteristics are all obtained this way.
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A dual trace oscilloscope differs from a dual beam instrument in that it
Answer: D
An electronic switch shares one gun between the two channels, which is far cheaper than a tube with two guns. The compromise is that neither channel is displayed continuously, so a genuinely simultaneous view of two single events needs a dual beam tube.
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In the alternate mode of a dual trace oscilloscope the two channels are displayed
Answer: A
Channel one is drawn for a whole sweep, then channel two for the next, and so on. At fast sweep speeds the eye blends them into two steady traces, so the mode suits high frequency work; at slow speeds the traces are seen to flicker alternately.
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The chop mode of a dual trace oscilloscope is preferred at
Answer: B
Chopping switches between the channels many times within one sweep, so both appear on every sweep and neither flickers at slow speeds. At fast speeds the chopping rate becomes comparable with the signal and the traces break into visible dashes.
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