Question E5C04:
What type of Y-axis scale is most often used for graphs of circuit frequency response?  

Choices:  
A: Linear  
B: Scatter  
C: Random  
D: Logarithmic    

Correct Answer is  D: Logarithmic  

Correct Answer: D — Logarithmic

Why D is correct:
- Circuit frequency response is typically plotted as gain or attenuation versus frequency.
- The gain is almost always shown in decibels (dB), which is a logarithmic measure. This compresses a wide dynamic range and makes multiplicative changes appear as additive steps, which is easier to interpret.
- Common “Bode magnitude” plots use a dB Y-axis, so the Y-axis is logarithmic.

Useful formulas:
- Power ratio to dB: $$G_{dB} = 10 \log_{10}\!\left(\frac{P_2}{P_1}\right)$$
- Voltage (or current) ratio to dB: $$G_{dB} = 20 \log_{10}\!\left(\frac{V_2}{V_1}\right)$$
- Rules of thumb:
  - Doubling power ≈ +3 dB; 10× power = +10 dB
  - Doubling voltage ≈ +6 dB; 10× voltage = +20 dB
  - First-order roll-off: 20 dB/decade (≈6 dB/octave)

Why the other choices are incorrect:
- A: Linear — Sometimes used, but it does not handle wide dynamic ranges well; key features can be compressed or invisible compared to a dB scale.
- B: Scatter — This describes a plot type, not a Y-axis scale.
- C: Random — Not a recognized axis scale.