Step 1: Recall formula from photogrammetry.
The relationship is derived from the similarity of triangles in aerial photogrammetry:
\[
\frac{B}{b} = \frac{H}{f}
\]
Step 2: Rearrange.
\[
B = \frac{bH}{f}
\]
Step 3: Conclusion.
The correct formula is $B = \dfrac{bH}{f}$, so option (A) is correct.
A weight of $500\,$N is held on a smooth plane inclined at $30^\circ$ to the horizontal by a force $P$ acting at $30^\circ$ to the inclined plane as shown. Then the value of force $P$ is:
A steel wire of $20$ mm diameter is bent into a circular shape of $10$ m radius. If modulus of elasticity of wire is $2\times10^{5}\ \text{N/mm}^2$, then the maximum bending stress induced in wire is: