Question

Difficulty: HardMeasurement of Time

A ticker-tape timer connected to a 50 Hz50\text{ Hz} alternating current mains supply is used to measure the time interval of a laboratory cart moving down an inclined plane. On the printed tape, 1010 distinct tick spaces are recorded between the initial and final position. A electronic stopwatch running concurrently has a positive zero error of +0.04 s+0.04\text{ s}. What is the true elapsed time interval represented by the ticker tape after properly correcting for the stopwatch zero error?

  1. 0.16 s0.16\text{ s}Answer
  2. B
    0.24 s0.24\text{ s}
  3. C
    0.20 s0.20\text{ s}
  4. D
    0.22 s0.22\text{ s}

Answer

The true elapsed time interval is 0.16 s0.16\text{ s}.
The ticker-tape frequency of 50 Hz50\text{ Hz} gives a time interval of 0.02 s0.02\text{ s} per space. Ten tick spaces correspond to an uncorrected time of 0.20 s0.20\text{ s}. To correct for a positive zero error of +0.04 s+0.04\text{ s}, the zero error must be subtracted from the uncorrected reading, yielding a true elapsed time of 0.16 s0.16\text{ s}.

Step-by-Step Solution

1
Calculate the period of a single tick interval
T=1f=150 Hz=0.02 sT = \frac{1}{f} = \frac{1}{50\text{ Hz}} = 0.02\text{ s}
Frequency ff is the inverse of period TT for a ticker-tape timer.
2
Determine the uncorrected total elapsed time from tick spaces
tuncorrected=10×0.02 s=0.20 st_{\text{uncorrected}} = 10 \times 0.02\text{ s} = 0.20\text{ s}
Elapsed time equals the number of tick spaces multiplied by the period of one space.
3
Apply the zero error correction
ttrue=tuncorrectedzero error=0.20 s0.04 s=0.16 st_{\text{true}} = t_{\text{uncorrected}} - \text{zero error} = 0.20\text{ s} - 0.04\text{ s} = 0.16\text{ s}
True Reading = Observed Reading - (Zero Error).

Key Concept

Measurement of time using ticker-tape timers and instrument zero error correction
Estimated Time:1m 30s
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