MCQ
For light diverging from a point source:
- AThe wavefront is spherical.
- BThe intensity decreases in proportion to the distance squared.
- CThe wavefront is parabolic.
- DThe intensity at the wavefront does not depend on the distance.
✓
Answer
- The wavefront is spherical.
- The intensity decreases in proportion to the distance squared.
Solution:
| Type of wavefront | Intensity | Amplitude |
 | $\text{I}\propto\frac{1}{\text{r}^2}$ | $\text{A}\propto\frac{1}{\text{r}}$ |
 | $\text{I}\propto\frac{1}{\text{r}}$ | $\text{A}\propto\frac{1}{\sqrt{\text{r}}}$ |
 | $\text{I}\propto\text{r}^0$ | $\text{A}\propto\text{r}^0$ |
Due to the point source light propagates in all directions symmetrically and hence, wevefront will be spherical as shown in the diagram.
As intensity of the source will be,
$\text{I}\propto\frac{1}{\text{r}^2}$
where, r is radius of the wavefront at any time
Hence the intensity decreases in proportion to the distance squared.
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