1. (i) when
(two) waves meet/combine/interact/superpose, etc. (at a point)
M1
there is a change in overall
intensity/displacement
allow
for A1 mark: (vector) sum/resultant displacement(s)/AW
A1
(ii) constant
phase difference/relationship (between the waves)
just
stating same frequency not sufficient
B1
[3]
9. constructive interference:
valid diagram and/or explanation: e.g.
when
waves (from coherent sources) meet in phase (or nl path diff.) B1
waves
reinforce: resultant has increased displacement/amplitude B1
correctly
shown on diagram or stated
destructive
interference: valid diagram and/or explanation: e.g.
when
waves meet in antiphase/180° phase diff. {or (n + 1/2) l path diff.} B1
waves
cancel: resultant has reduced displacement/amplitude B1
correctly
shown on diagram or stated
[4]
