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<math>x(t)= e^{-2\pi jt} </math> | <math>x(t)= e^{-2\pi jt} </math> | ||
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==Answer 1=== | ==Answer 1=== | ||
<math> | <math> | ||
\begin{align} | \begin{align} | ||
| − | E_{\infty}&=\int_{-\infty}^\infty | | + | E_{\infty}&=\int_{-\infty}^\infty |e^{-2\pi jt}|^2 dt \\ |
| − | &=\int_{-\infty}^\infty | + | &=\int_{-\infty}^\infty e^{-2\pi jt} * e^{2\pi jt} dt \\ |
| − | + | &=\int_{-\infty}^\infty (1) dt \\ | |
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| − | &=\int_{-\infty}^\infty | + | |
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&=\infty | &=\infty | ||
\end{align} | \end{align} | ||
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<math> | <math> | ||
\begin{align} | \begin{align} | ||
| − | P_{\infty}&=\lim_{T\rightarrow \infty} {1 \over {2T}} \int_{-T}^T | | + | P_{\infty}&=\lim_{T\rightarrow \infty} {1 \over {2T}} \int_{-T}^T |e^{2\pi jt}|^2 dt \quad \\ |
\text{Similar to math above, the expression can be derived towards}\\ | \text{Similar to math above, the expression can be derived towards}\\ | ||
| − | &= \lim_{T\rightarrow \infty} {1 \over {2T}} (\int_{-T}^T | + | &= \lim_{T\rightarrow \infty} {1 \over {2T}} (\int_{-T}^T (1) dt) \quad \\ |
| − | & = \lim_{T\rightarrow \infty} {1 \over {2T}} ( | + | & = \lim_{T\rightarrow \infty} {1 \over {2T}} (t \Big| ^T _{-T}) \quad \\ |
| − | & = \lim_{T\rightarrow \infty} {1 \over {2T}} ( | + | & = \lim_{T\rightarrow \infty} {1 \over {2T}} (T + T) \quad \\ |
| − | & = \lim_{T\rightarrow \infty} {1 \over {2T}} ( | + | & = \lim_{T\rightarrow \infty} {1 \over {2T}} (2T) \quad \\ |
| − | &= \lim_{T\rightarrow \infty} | + | &= \lim_{T\rightarrow \infty} (1) \quad \\ |
| − | &= | + | &= 1 \quad \\ |
| − | + | ||
\end{align} | \end{align} | ||
</math> | </math> | ||
| − | So <math class="inline">P_{\infty} = | + | So <math class="inline">P_{\infty} = 1 </math>. |
Latest revision as of 09:22, 22 January 2018
Practice Question on "Signals and Systems"
Topic: Signal Energy and Power
Question
Compute the energy $ E_\infty $ and the power $ P_\infty $ of the following continuous-time signal
$ x(t)= e^{-2\pi jt} $
Answer 1=
$ \begin{align} E_{\infty}&=\int_{-\infty}^\infty |e^{-2\pi jt}|^2 dt \\ &=\int_{-\infty}^\infty e^{-2\pi jt} * e^{2\pi jt} dt \\ &=\int_{-\infty}^\infty (1) dt \\ &=\infty \end{align} $
So $ E_{\infty} = \infty $.
$ \begin{align} P_{\infty}&=\lim_{T\rightarrow \infty} {1 \over {2T}} \int_{-T}^T |e^{2\pi jt}|^2 dt \quad \\ \text{Similar to math above, the expression can be derived towards}\\ &= \lim_{T\rightarrow \infty} {1 \over {2T}} (\int_{-T}^T (1) dt) \quad \\ & = \lim_{T\rightarrow \infty} {1 \over {2T}} (t \Big| ^T _{-T}) \quad \\ & = \lim_{T\rightarrow \infty} {1 \over {2T}} (T + T) \quad \\ & = \lim_{T\rightarrow \infty} {1 \over {2T}} (2T) \quad \\ &= \lim_{T\rightarrow \infty} (1) \quad \\ &= 1 \quad \\ \end{align} $
So $ P_{\infty} = 1 $.
