Energy of a signal depends upon

1. Magnitude spectrum of Fourier transform only
2. Phase spectrum of Fourier transform only
3. Both Magnitude and phase spectrum of Fourier transform
4. None of these

According to the Parsevel’s theorem for energy signals.

i.e., E =		^∞	\|F(ω)\|²df
		_{- ∞}

From this relation it is clear that energy of a signal depends only upon the magnitude spectrum of Fourier transform.