## Did you know, that the most common feedback about the NCEES Electrical Power PE Exam is that exam takers are often surprised at the high number of qualitative questions that appear on the exam?

A qualitative question is a test question designed to test your application of theory to select the most appropriate answer and usually does not involve any math.

There are two main types of questions on the PE exam.

**Quantitative Question** – A question that asks for a quantity value, typically a numerical value. It relies on using math and formulas to solve.

**Qualitative Question** – A question that asks for the most accurate quality or description. It usually involves no numbers.

Below is a quiz question taken directly from the Power Supplies Module in our Online Course to give you a better idea of qualitative questions and the different strategy you can use to help you solve them:

### II.B.2. Power Supplies Quiz

**Question 9 – Compared to a half wave rectifier, a full wave rectifier differs most nearly in that:**

#### A) The average voltage output will be larger in value.

#### B) The average voltage output will be smaller in value.

#### C) It will require a larger peak voltage AC input signal to account for the three additional diodes.

#### D) The instantaneous input power seen at the power source will have a frequency twice as big as both the frequency of the instantaneous input voltage and current.

(Scroll down for the solution)

### Solution:

Compare the output graph of the half wave rectifier to the full wave rectifier over the same period and you will notice that the full wave rectifier has two positive half cycles and the half wave rectifier only has one:

This means that the resulting average voltage output, also known as the DC voltage found using the below formula where F(t) equals the instantaneous output voltage function:

Will be much **larger** than the half wave rectifier.

The correct answer is:

**A) ****The average voltage output will be larger in value.**

### Wrong Answers:

**B) The average voltage output will be smaller in value. **

The Opposite is true since we now have twice as many half cycles in the same period.

**C) It will require a larger peak voltage AC input signal to account for the three additional diodes.**

Although real diodes do exhibit a very small measurable voltage drop, it is considered negligible in power circuits. Therefore a few extra diodes do not generally require a larger AC input voltage to operate.

**D) The instantaneous input power seen at the power source will have a frequency twice as big as both the frequency of the instantaneous input voltage and current. **

This is true for both the full wave and half wave rectifier looking at the power source since instantaneous power is the product of instantaneous voltage and instantaneous current:

p(t)=v(t)i(t).

Anmar Hiassat says

This article was the key that helped me work this kind of problems much much much more better

Abhishek says

I was afraid to learn and solve problems for this topic but you made it look so simple and easy to understand. Thank you.

Egis says

Electronics bin always hard to understand for me, but watching your videos really makes things more simple and easier to understand. Probably will not make me expert but defiantly changed my thinking during the problems.

Sam says

Always explained clearly and concisely! Thanks for being a great resource.

Orlando says

This out of many other things in this course is extremely help. This material has helped me understand the basics of Power engineering. Highly recommend this course.

Carlos Cifuentes says

Zach,

Power supplies really helped me a lot. It definitely made me have a better understanding of how it works. You honestly have the gift of teaching.

Zach Stone, P.E. says

Thanks for the compliment Carlos! I’m glad it has been helpful to you

Jeff Beer says

The Electrical PE Review module, “Devices & Power Electronics”, was excellent. There are multiple PE Exam practice questions which ask for the correct solution output waveform based on the power electronic circuit problem. Before I took the Electrical PE Refresher course, I had great difficulty in determining what the correct output would be for those various circuit configurations. Now I can solve them both quickly and accurately. I now have a great feeling of confidence when seeing these problems and look forward to getting that much more correct answers on the PE Exam!

Zach Stone, P.E. says

Thanks Jeff! I’m glad you have been enjoying the course and that it has been helpful for you.

Patrick says

This section has definitely strengthened my conceptual understanding of power supplies. Sometimes its easy to forget the big picture when sifting through formulas. This is a big help!