For sustained interference fringes in double slit experiment, essential condition/s is/are

(a) sources must be coherent

(b) the intensities of the two sources must be equal

Here, the correct options is/are

CONCEPT: 

• Interference: The combination of two or more electromagnetic waveforms to form a resultant wave that may have greater, lower, or the same amplitude is called interference.
• YDSE (Young’s Double Slit Experiment): If a monochromatic light falls on two narrow slits which are very close to each other act as coherent source superpose each other and an interference pattern is observed on the screen.

• Condition for Obtaining Clear and Broad Interference Bands
  • The screen should be far away from the source.
  • The wavelength of light used must be larger.
  • The two coherent sources should be very close.
  • Two sources of light must be of the same frequency.
  • The amplitude of interfering light waves must be the same.

EXPLANATION:​​​

• From the definition of the interference of the double-slit experiment;
  • Sources should be coherent.
  • But they may or may not have equal intensity.
• So the correct answer is option 2.