The unit used to measure electric current is the ampere (AA). Now, assume that the current delivered at a wall socket reaches the value 3.8 AA ten times in a time interval of 0.17 ss. What is the period TTT with which the current at the wall socket changes?

The period T with which the current at the wall socket changes is 0.017 s.

It also ranges from 0.155 s to 0.0189 s since the cycles is not given in the question.

Explanation:

The current reaches 3.8 A once for every cycle. So there must have been 10 cycles (10 periods) in 0.17 s.  

Using 'T' for period:

                                10 T = 0.17  

                                      T = 0.17 / 10  

                                     T  = 0.017 s.

The question doesn't tell about the cycles and so we assume it as 10 cycles. If there are 9 cycles due to the current 3.8 A at the exact beginning and end of 0.17 s. This would make the period T as

                              0.17 / 9 = 0.0189 s approx.

Likewise, if the 3.8 A occurs at the end of the 1st cycle, 11 cycles would have passed during 0.17 s.

In that case the period = 0.17 / 11 = 0.155 s approx.

So T could be in the range from 0.155 s to 0.0189 s.

d. air pressure decreases as altitude increases.