Chapter 11: Problem 9
Sketch the graph of the given cylindrical or spherical equation. $$ \phi=\pi / 6 $$
Short Answer
Expert verified
The graph is a double cone centered at the origin, with an apex angle of \( \pi/6 \).
Step by step solution
01
Understanding the Spherical Coordinates
In spherical coordinates, a point is described by three parameters: \( (\rho, \theta, \phi) \). Here, \( \rho \) is the radial distance from the origin, \( \theta \) is the azimuthal angle in the \( xy \)-plane from the positive \( x \)-axis, and \( \phi \) is the polar angle from the positive \( z \)-axis.
02
Identifying the Surface
The equation given is \( \phi=\pi/6 \). This specifies that the polar angle \( \phi \) is constant, which describes a conical surface. The surface consists of a cone centered around the \( z \)-axis with the angle at the apex being \( \pi/6 \) radians.
03
Visualizing the Shape
A cone with an apex angle of \( \pi/6 \) has its apex at the origin and opens upward and downward around the \( z \)-axis. The cross-section in any plane containing the \( z \)-axis will show lines meeting at the origin, forming an angle of \( \pi/6 \) with the \( z \)-axis.
04
Drawing the Graph
To sketch the graph, begin by drawing the \( z \)-axis. Then, draw straight lines representing the conical surface. These lines should form an angle of \( \pi/6 \) with the \( z \)-axis, extending symmetrically around it to create a double cone (one part above and one part below the \( xy \)-plane).
05
Completing the Sketch
Ensure the completed drawing shows two cones meeting at the origin. The cones should be symmetrical and smooth, accurately reflecting the \( \pi/6 \) angle to the \( z \)-axis. This completes the graph of the spherical equation.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Spherical Coordinates
Spherical coordinates offer a unique way to describe points in three-dimensional space. Unlike Cartesian coordinates which use x, y, and z axes, spherical coordinates utilize three parameters:
For example, a sphere centered at the origin has a simple equation in spherical coordinates: \( \rho = R \), where R is the radius. Compared to Cartesian coordinates, spherical coordinates can simplify many geometrical problems.
- \( \rho \): This is the radial distance from the origin to the point.
- \( \theta \): The azimuthal angle, measured in the xy-plane from the positive x-axis.
- \( \phi \): Known as the polar angle, it is the angle measured from the positive z-axis.
For example, a sphere centered at the origin has a simple equation in spherical coordinates: \( \rho = R \), where R is the radius. Compared to Cartesian coordinates, spherical coordinates can simplify many geometrical problems.
Cone Surface
When a spherical equation specifies a constant polar angle, such as \( \phi=\pi/6 \), this defines a cone surface. This concept can be visualized as a 3D cone, with the following characteristics:
- It is centered around the z-axis. The z-axis acts like the spine of the cone, going through its center.
- The apex of the cone is located at the origin of the spherical coordinate system.
- The apex angle, which is \( \phi = \pi/6 \), determines how "wide" or "narrow" the cone is. A smaller \( \phi \) means a narrower cone.
Polar Angle
The polar angle, \( \phi \), is a core component of spherical coordinates with pivotal roles in geometry representation.
Each point on this conical surface maintains this \( \phi \) angle from the z-axis, making the understanding of polar angles essential to sketching or conceptualizing spherical shapes, particularly cones.
- It measures the angle from the positive z-axis to the point of interest.
- A polar angle of \( 0 \) means the point is directly above the z-axis, at the top of the axis (like the North Pole on a globe), while a polar angle of \( \pi \) places it directly below.
Each point on this conical surface maintains this \( \phi \) angle from the z-axis, making the understanding of polar angles essential to sketching or conceptualizing spherical shapes, particularly cones.