Paper 1 Superposition of Waves Answers

Q	Ans	Brief reason
1	B	Displacements add algebraically/vectorially.
2	B	Constructive condition is integer wavelength path difference.
3	C	Odd multiples of $\pi$ are antiphase.
4	B	Coherence requires fixed phase relationship.
5	A	Small-angle double-slit formula.
6	B	$x\propto 1/a$.
7	B	Opposite-travelling identical waves form stationary waves.
8	B	Nodes have zero amplitude.
9	B	Node spacing is half a wavelength.
10	B	Fundamental fixed-string mode has two nodes and one antinode.
11	B	Diffraction is large when aperture is comparable to wavelength.
12	A	First-minimum single-slit condition.
13	A	Grating principal maxima condition.
14	B	Central maximum is about twice side-maxima width.
15	B	$\sin \theta =n\lambda /d$.
16	B	Rayleigh criterion is about just-resolved images.
17	A	Superposition does not change source frequency.
18	B	Stationary wave has no net energy transfer along the pattern.
19	A	Open ends are displacement antinodes.
20	A	Integer path difference gives constructive interference.