# Electronic Devices and Circuits Questions and Answers – The Decibel

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “The Decibel”.

1. What is the symbol of a decibel?
a) dB
b) Db
c) DB
d) db

Explanation: The decibel is a comparative unit of measurement equivalent to one tenth (deci) of a Bel unit. A Bel unit is expressed as B and hence the decibel is subsequently expressed by the symbol dB. They are a unit of a logarithmic scale to measure power or intensity levels.

2. What is the corresponding change in level for a factor of 10 change in power?
a) 100dB
b) 20dB
c) 10dB
d) 0.1dB

Explanation: A decibel is ten times the value of power in its logarithm in base 10. Therefore a 10dB change is resultant of a change in power by a factor of 10. However, when calculating in terms of amplitude the change is due to a factor on 20.

3. What is the corresponding change in level for a factor of 10 change in amplitude?
a) 100dB
b) 20dB
c) 10dB
d) 0.1dB

Explanation: A decibel is ten times the value of power in its logarithm in base 10. Therefore a 20dB change is resultant of a change in amplitude by a factor of 10. However, when calculating in terms of power the change is due to a factor on 10.

4. What is the value of voltage gain in decibels if Voutput = 20V and Vinput = 15V?
a) 1.75dB
b) 2.28dB
c) 1.37dB
d) 2.48dB

Explanation: The voltage gain in terms of decibels is expressed as 20 × log (Voutput / Vinput) . Given, Voutput = 20V and Vinput = 15V.
Voltage gain = 20 × log (Voutput / Vinput) = 20 × log (1.33) = 20 × 0.1239 = 2.48dB.

5. What is the value of power gain in decibels if Poutput = 250W and Pinput = 100W?
a) 2.48dB
b) 3.98dB
c) 1.78dB
d) 3.54dB

Explanation: The power gain in terms of decibels is expressed as 10 × log (Poutput / Pinput) . Given, Poutput = 250W and Pinput = 100W
Power gain = 10 × log (Poutput / Pinput) = 10 × log (2.5) = 10 × 0.3979 = 3.98dB.

6. How is the power ratio corresponding to 12dB change in level?
a) 16.38
b) 14.24
c) 15.85
d) 12.88

Explanation: To calculate the power ratio corresponding to 12dB change in level:
G = 10(12 / 10) × 1 = 101.2 = 15.85.

7. What is dBFS used to measure in terms of decibels?
a) Peak amplitude of a signal
b) Power relative to 1mW
c) Amplitude of a signal
d) Volume unit

Explanation: We use dBFS to measure the amplitude of a signal in comparison to the maximum value a device could handle prior to clipping. FS stands for full scale and is used to define the power level sinusoid or a full scale square wave.

8. The symbols dBA, dBB and dBC are used for to estimated human ear’s reaction to sound.
a) True
b) False

Explanation: The symbols dBA, dBB and dBC are used for to estimated human ear’s reaction to sound. They all fall under the subcategory of dB SPL which stands for sound pressure level. They are all weighted measures and are used to refer to the effects of noise on human and animals’ ears.

9. What is dBTP used to measure in terms of decibels?
a) Peak amplitude of a signal
b) Power relative to 1mW
c) Amplitude of a signal
d) Volume unit

Explanation: We use dBTP to measure the peak amplitude of a signal in comparison to the maximum value a device could handle prior to clipping. TP stands for true peak and the values measured are always negative or zero since they are less compared to the full scale values.

10. What is dBm used to measure in terms of decibels?
a) Peak amplitude of a signal
b) Power relative to 1mW
c) Amplitude of a signal
d) Volume unit

Explanation: We use dBm to measure the power relative to 1mW. It is generally compared relative to a 600Ω impedance, which equates to a voltage level of 0.775V. The m stands for milliwatts. The derivate dBm0 stands for dBm measured at zero transmission level point.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

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