Interference fringes may be observed due to the superposition of two light waves represented by:

$y_1 = 2a \sin 2ωt$ and $y_2 = 2a\sin 2(ωt + δ)$

The correct answer is Option (3) → $y_1 = 2a \sin 2ωt$ and $y_2 = 2a\sin 2(ωt + δ)$

Interference occurs when two light waves have the same frequency (or angular frequency) so that a stable phase difference exists. Waves with different frequencies do not produce stationary interference fringes.

Among the given options, only:

$y_1 = 2 \sin 2 \omega t$ and $y_2 = 2 \sin 2 (\omega t + \delta)$

have the same frequency ($2\omega$), so they can produce interference fringes.

Final Answer: $y_1 = 2 \sin 2 \omega t$ and $y_2 = 2 \sin 2 (\omega t + \delta)$