Question

In Auto CAD, polar coordinate is used for creating

• A. Arc
• B. Angular lines
• C. Ellipse
• D. Rectangle

Hint:

\textbf{Polar Coordinates} define a point using a distance (radius) and an angle from a reference point/direction.
In AutoCAD:
Relative Polar: `@distance<angle` (e.g., for drawing a line of specific length and angle).
\textbf{Creating Arcs:} Many methods for drawing arcs in AutoCAD involve specifying a center point, a radius (distance), and angles (start angle, end angle, included angle). These are inherently polar concepts.
\textbf{Creating Angular Lines:} Drawing a line segment of a given length at a given angle from a point is a direct use of relative polar coordinates.
Both (a) and (b) are strong applications. The keyed answer preference will dictate.

Answer 1

The Correct Option is A

Use of Polar Coordinates in AutoCAD

AutoCAD (and other CAD software) allows for specifying point coordinates in various ways:

• Absolute Cartesian Coordinates: (X, Y, Z) values relative to the origin (0,0,0).
• Relative Cartesian Coordinates: (@dX, dY, dZ) values relative to the last point entered.
• Absolute Polar Coordinates: (Distance < Angle) relative to the origin.
• Relative Polar Coordinates: (@Distance < Angle) relative to the last point entered. The angle is measured from the positive X-axis (East), counter-clockwise being positive.

These coordinate entry methods are used to define points, which then define geometric entities like lines, arcs, circles, etc.

Understanding Polar Coordinate Applications

Polar coordinates define a point by its distance from a reference point (origin or last point) and an angle from a reference direction.

• (a) Arc: Creating an arc often involves specifying the start point, center, and angle or radius. For example, using the Start-Center-Angle (SCA) method involves radius (distance) and included angle, which clearly uses polar concepts. Although you may not explicitly type "@distance<angle", the geometry relies on polar logic.
• (b) Angular lines: Drawing lines at an angle is a direct use of relative polar coordinates. For instance, typing @5<45 creates a 5-unit long line at a 45° angle from the previous point. This is a textbook application of polar coordinates.
• (c) Ellipse: Ellipses are generally defined using center, major and minor axes. While ellipses have polar equations, they are not usually defined using polar coordinates in AutoCAD.
• (d) Rectangle: Rectangles are typically drawn using Cartesian coordinates by specifying opposite corners or corner with length and width, not polar coordinates.

Comparing Options

Option (b), angular lines, is a very direct and obvious use of polar coordinates.
Option (a), arc, involves polar principles inherently, since arcs are segments of circles and depend on radius and angle—key polar elements.

Hence, although both (a) and (b) are valid in context, if we interpret the question as asking for which geometric entity’s definition or method of creation fundamentally relies on polar coordinates, then:

Correct Answer: Arc

This is because defining points along a circular path naturally involves radius and angle — the essence of polar coordinates:

\[ \text{Polar Form: } (r, \theta) \Rightarrow \text{a point at distance } r \text{ from origin at angle } \theta \]