An alternative focal depth formula is focal depth (cm) = (diameter (mm)^2 / 40) x wavelength (mm). Which option matches this exactly?

An alternative focal depth formula is focal depth (cm) = (diameter (mm)^2 / 40) x wavelength (mm). Which option matches this exactly?

• A. focal depth (cm) = diameter (mm)^2 / 40 x wavelength (mm)
• B. focal depth (cm) = (diameter (mm)^2 / 40) x wavelength (mm)
• C. focal depth (cm) = diameter (mm)^2 x wavelength (mm) / 40
• D. focal depth (cm) = diameter (mm)^2 x 40 / wavelength (mm)

Answer: (B)

The key idea is to follow the exact grouping shown and apply the order of operations accordingly. The focal depth is defined as the diameter in millimeters squared, divided by 40, then multiplied by the wavelength in millimeters. The expression that matches this precisely is the one with parentheses around the first part: (diameter (mm)^2 / 40) x wavelength (mm). This makes clear you first square the diameter, then divide by 40, and only after that multiply by the wavelength. Other forms change the visible grouping and could be read differently, even though some rearrangements may numerically align; sticking to the parentheses preserves the intended order and exactly mirrors the given formula.

The key idea is to follow the exact grouping shown and apply the order of operations accordingly. The focal depth is defined as the diameter in millimeters squared, divided by 40, then multiplied by the wavelength in millimeters. The expression that matches this precisely is the one with parentheses around the first part: (diameter (mm)^2 / 40) x wavelength (mm). This makes clear you first square the diameter, then divide by 40, and only after that multiply by the wavelength. Other forms change the visible grouping and could be read differently, even though some rearrangements may numerically align; sticking to the parentheses preserves the intended order and exactly mirrors the given formula.