## 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).

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