A radio transmission costing 100 \( \mu \)J is sent once a minute. Its contribution to the average power is about
Answer: C
A hundred microjoules in sixty seconds is 1.67 microwatts, which at three volts is about half a microampere. Comparing that against the sleep current shows at once whether the radio or the sleeping electronics dominates the budget.
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For that same design, sending once a second instead would raise the radio's contribution to about
Answer: D
A hundred microjoules every second is a hundred microwatts, sixty times the previous figure and now certainly the dominant term. Reporting interval is therefore the single most powerful lever in a wireless sensor's energy budget.
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Comparing a design reporting every second with one reporting every minute, the battery life is longer by a factor of roughly
Answer: A
Only the term that dominates scales the answer: where the radio is almost the whole budget the improvement approaches the ratio of the intervals, and where sleep current dominates it is much smaller. Knowing which term dominates is the point of building the budget.
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