A reader of this 4th edition points out a flawed question in the Part I test. It's question 14 on page 134. Here's my e-mail exchange with that reader, with the name changed to "Reader" to protect the identity. Please discard Question 14, so the Part I test will have only 49 questions.

On Thu, May 31, 2012 at 12:26 AM, Reader wrote:

Dear Sir,

I'm studying your excellent book (4th edition) to gain more knowledge about electronics. I'm currently done with Part 1, but I have a question with "Test: Part 1," Question 14 (p.134).

The correct answer is given as (c). Is it ever possible for an AC signal to have a peak voltage equal to its average value? Are you suggesting that it may be a complex waveform (not sine-wave) and the peak is also equal to average? I couldn't come up with such a shape myself and I was thinking maybe (a) might be the correct answer?

Thank you for your time.


Dear Reader:

First of all, thanks for the kind words about my book.

As for the test question, if we interpret "peak voltage" as "positive peak voltage," then you are right, the answer should be (a). If we interpret it as "negative peak voltage," then the answer would be (b). If we interpret it as "the maximum extent to which the waveform departs from the average voltage," then we could in fact have a "peak voltage" that's the same as the average voltage if we had an AC wave with a DC component equal to the maximum extent to which the voltage varies above or below that component.

But now as I think about it, this question should be thrown out altogether because it's ambiguous! Moreover, it has no business being in Part I. The book doesn't get into AC until Chapter 9, which is in Part II.

In the fifth edition of this book, I have added an extra paragraph in Chapter 9 that distinguishes more rigorously between "positive peak voltage" and "negative peak voltage." We might then rewrite the question you mention as:

"The positive peak voltage in an AC wave is always ..."

In that case, none of the answers given here would be correct at all! The positive peak voltage is the maximum extent to which the wave gets more positive than the average voltage. In an AC wave with no DC component, the correct answer would be (a). However, with DC components that might go either positive or negative, we could find waves for which any of the answers would work except (e).

In retrospect, I can't imagine how that question got in there, except that I wasn't paying enough attention, maybe hadn't had enough coffee that morning.

I'll see what I can do to add a correction page on my Web site about this -- probably just recommend that readers ignore this question as ambiguous and out-of-place. That would make the Part I test only 49 questions long.

In the fifth edition, I rewrote all of the quiz and test questions, so hopefully this question isn't in the new edition anywhere at all.

Best regards,