Two Source Interference

• Only coherent sources can form an interference pattern
• Waves are coherent when they have a constant phase difference
• When two waves meet in phase and with a path difference of n λ, they constructively interfere
• When two waves meet in antiphase and with a path difference of (n+1/2) λ, they destructively interfere
• The central maximum has zero phase difference
• Points of constructive interference are joined by antinodal lines
• Points of destructive interference are joined by nodal lines
• Dark spots are formed at minima due to wave cancellation