Express the power dissipated in a 100 Ω resistor in dB relative to 1 mW, when the voltage across the resistor is 1.0 Vrms

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URSC ISRO Technical Assistant Electronics 24 March 2019 Official Paper
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  1. 100 dB
  2. 20 dB
  3. 10 dB
  4. 1 dB

Answer (Detailed Solution Below)

Option 3 : 10 dB
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The voltage across the resistor = 1 Vrms

Resistance Value = 100 Ω

The power dissipated by the resistor is given by:

\(P = \frac{V_{rms}^2}{R}\)

\(P = \frac{1^2}{100}=\frac{1}{100}=10^{-2}~W\)

We are asked to evaluate the power dissipated with respect to 1 mW reference power.

\(P=\frac{10^{-2}}{10^{-3}}=10\)

In dB, this is expressed as:

\(P_{dB}=10~log_{10}(P)=10~log_{10}\frac{10^{-2}}{10^{-3}}\)

PdB = 10 log10(10) = 10 dB

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