Question 1: 1. A student used the experimental setup shown in Figure A to study the phenomenon of interference a...
1. A student used the experimental setup shown in Figure A to study the phenomenon of interference and diffraction of light, the width of the slit $S _ { 1 } , S _ { 2 }$ $d$ can be adjusted, the slit to the screen distance is $L$. The same monochromatic light irradiated perpendicular to the slit, the experiment was obtained on the screen Figure B, Figure C shown in the pattern. The following description is correct ( )  A  B  C
- A. A. Figure B shows the diffraction pattern of light
- B. B. When irradiating two slits, increasing the width of the slits, all else being equal, increases the distance between the centers of adjacent dark stripes in Figure B.
- C. C. When illuminating both slits, increasing the distance $L$, other things being equal, the distance between the centers of the adjacent dark stripes in Fig. B increases
- D. D. When two slits are illuminated, if the difference in the distance traveled by light from the slit ${ } ^ { S _ { 1 } , S _ { 2 } }$ to the $P$ point on the screen is an odd multiple of the half-wavelength, there must be a bright stripe at the $P$ point.
Answer: C
Solution: A. The stripes in Figure B are equally spaced, so it is a double-slit interference stripe pattern, A is wrong;
BC. according to the interference formula
$$
\lambda = \frac { L \lambda } { d }
$$
When increasing the slit width $d$ other unchanged, the center spacing of interference fringes decreases, when increasing the distance $L$ other unchanged, the center spacing of interference fringes increases, B is wrong, C is correct;
D. When the distance difference of the light is an odd multiple of the half wavelength, it is the mutual weakening zone, i.e., the dark fringe, so the P point must be the dark fringe, D is wrong.