A) \[71.6{}^\circ \]
B) \[45{}^\circ \]
C) \[90{}^\circ \]
D) \[18.4{}^\circ \]
Correct Answer: D
Solution :
| [d] \[\text{l}\,\,\text{=}\,\,{{\text{l}}_{\text{0}}}{{\cos }^{2}}\theta \] |
| \[\Rightarrow \frac{{{\text{l}}_{\text{0}}}}{\text{10}}\,\,\text{=}\,\,{{\text{l}}_{\text{0}}}{{\cos }^{2}}\theta \] |
| \[\Rightarrow \frac{1}{10}={{\cos }^{2}}\theta \] |
| \[\Rightarrow \cos \theta =\frac{1}{\sqrt{10}}=0.316\] |
| \[\Rightarrow \theta \approx 71.6{}^\circ \] |
| \[\therefore \phi =90-\theta -71.6=18.4{}^\circ \] |
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