Skip distance S in a plate is given by which formula?

• A. S = 2 x V x sinθ
• B. S = (2 x t) / tanθ
• C. S = 2 x t x tanθ
• D. S = 2 x t x sinθ

Answer: (C)

When using an angle beam in a plate, the skip distance is the lateral offset along the surface between the entry point and where the back-wall echo emerges. The beam travels from the surface to the back of the plate and back again, so there are two equal leg paths inside the thickness t. If the beam makes an angle θ with the normal inside the plate, the horizontal shift for one leg is t tan θ (from basic trigonometry: opposite = t, adjacent = t; horizontal displacement = t tan θ). Doubling for the two legs gives the total skip distance: S = 2 t tan θ.

So the correct expression is S = 2 t tan θ. The other forms mix in velocity or use sine where tangent is appropriate for this right-triangle geometry, which doesn’t describe the lateral surface offset correctly.