I'm having a little trouble with these q's
Q1. Constructive interference occurs at a given point when:

A. The path difference between waves arriving from 2 sources at the point is equal to an integral number of wavelengths
B. Waves from 2 sources arrive at the point with the same phase
C. all of the other answers
D. The shape of the waves from 2 sources look the same at the point
E. Waves from 2 sources travel the same distance to reach the point

Q2. A saxophonist is playing in a small room. When she plays a sustained musical note (A - wavelength 0.375 m), there are clear diffraction minima outside the door. If the first minimum is at 35 degrees, what is the width of the door?

A. 0.4 m
B. 0.6 m
C. 0.65 m
D. 0.35 m
E. 0.45 m

Thanks

Q1. Constructive interference occurs when two waveforms are "in phase". This occurs from answers A,B,D, and E. Therefore answer C (all of the other answers) is the correct choice.

Q2. I think this is simply "single-slit diffraction". You can Google that if you wish. The formula that controls single-slit diffraction is

sin(\theta) = m(\frac {\lambda}{W})

where m is 1,2,3, etc.
λ is the wavelength of the wave
W is the width of the slit.

The equation gives the angles of diffraction maxima, and not minima. So we have to think here.

Given that λ is 0.375 Meters, there will be diffraction maxima at

\theta = arcsin(\frac {0.375}{W})

I think the first minimum would come half way before that. (This is the assumption that is probably wrong and is probably the reason for the error).

\theta = arcsin(\frac {0.1875}{W})

35\,degrees\, = arcsin(\frac {0.1875}{W})

\frac {0.1875}{sin(35)} = W

\frac {0.1875}{0.5736} = W

W \, \approx \, 0.32\,m

But that isn't one of the choices, so I probably didn't do it correctly. Maybe this can help you figure out what do do?

That's OK. Yeah, your working out will be helpful.

Just more questions...

q. In a Young's double-slit experiment, the slit separation is doubled. This will effect the fringe pattern by?
A decreasing the fringe intensity
B increasing the fringe intensity
C decreasing the fringe spread
D increasing the fringe spread

q. Destructive interference occurs at a given point when:
A Waves from 2 sources arrive at the point with the same phase
B The path difference between waves arriving from 2 coherent sources at the point is equal to half integral number of wavelengths
C Waves from 2 sources travel the same distance to reach the point
D The shape of the waves from 2 sources look the same at the point
E The path difference between waves arriving from 2 sources at the point is equal to an integral number of wavelengths

Thank-you

Another question

q. What happens to the form of an interference pattern if the slits are moved farther apart?

A pattern spreads out
B pattern compresses

Thanks

Slits move farther apart indicates that the pattern compresses.