Chapter 2: Problem 405
For the following exercises, the cylindrical coordinates of a point are given. Find its associated spherical coordinates, with the measure of the angle \(\varphi\) in radians rounded to four decimal places. \(\left(3, \frac{\pi}{2}, 3\right)\)
Short Answer
Expert verified
The spherical coordinates are \(\left(3\sqrt{2}, \frac{\pi}{2}, \frac{\pi}{4}\right)\).
Step by step solution
01
Understand Cylindrical Coordinates
In cylindrical coordinates, the point is given as \((r, \theta, z) = \left(3, \frac{\pi}{2}, 3\right)\). Here, \(r\) is the radial distance from the \(z\)-axis, \(\theta\) is the angle in the \(xy\)-plane from the positive \(x\)-axis, and \(z\) is the height above the \(xy\)-plane.
02
Convert to Spherical Radius \(\rho\)
The spherical radial coordinate \(\rho\) is calculated using the formula \(\rho = \sqrt{r^2 + z^2}\). Substituting the given values, we get:\[ \rho = \sqrt{3^2 + 3^2} = \sqrt{9 + 9} = \sqrt{18} = 3\sqrt{2} \].
03
Determine Spherical Angle \(\phi\)
The spherical angle \(\phi\) is the angle from the positive \(z\)-axis, calculated using the formula \(\tan \phi = \frac{r}{z}\). Substituting the given values, we find:\[ \tan \phi = \frac{3}{3} = 1 \].Thus, \(\phi = \frac{\pi}{4}\).
04
Spherical Angle \(\theta\)
In spherical coordinates, the angle \(\theta\) remains the same as in cylindrical coordinates. Therefore, \(\theta = \frac{\pi}{2}\).
05
Write Spherical Coordinates
The spherical coordinates \((\rho, \theta, \phi)\) are given by \(\left(3\sqrt{2}, \frac{\pi}{2}, \frac{\pi}{4}\right)\), where \(\rho\) is the radial distance, \(\theta\) is the azimuthal angle, and \(\phi\) is the polar angle.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Cylindrical Coordinates
Cylindrical coordinates are an extension of two-dimensional polar coordinates. They add a third dimension, making them suitable for representing points in three-dimensional space. In this coordinate system, each point is described by three values:
- **r (radial distance):** This is the distance from the point to the z-axis. In the given example, it's 3.
- **θ (azimuthal angle):** This represents the angle in the xy-plane, measured from the positive x-axis. In our case, this is \(\frac{\pi}{2}\).
- **z (height):** This is the height of the point above the xy-plane. Here, it's 3.
Coordinate Conversion
When converting from cylindrical to spherical coordinates, we change from \((r, \theta, z)\) to \((\rho, \theta, \phi)\). Here’s how each component transforms:
- **From r to \(\rho\):** The spherical radial distance \(\rho\) is found using \( \rho = \sqrt{r^2 + z^2} \). In the exercise, this calculation gives us \( 3 \sqrt{2} \).
- **The angle \(\theta\):** It remains unchanged in conversion from cylindrical to spherical. Thus, \(\theta\) stays as \(\frac{\pi}{2}\).
- **From z to \(\phi\):** The angle from the positive z-axis \(\phi\) is determined by \( \tan(\phi) = \frac{r}{z} \). This calculation results in \( \phi = \frac{\pi}{4} \).
Trigonometry
Trigonometry plays a crucial role in coordinate conversions, especially when transforming angles and distances. Understanding the relationships between angles and sides in triangles is key. Here are some important aspects:
- **Pythagorean Theorem:** Essential for calculating the spherical radius \(\rho\), given by \( \rho = \sqrt{r^2 + z^2} \).
- **Tangent Function:** To find the angle \(\phi\), the tangent function is employed, \( \tan(\phi) = \frac{r}{z} \). This helps translate vertical height and radial distance into a findable angle from the positive z-axis.
Radians Calculation
Radians are a measure of angle used widely in mathematics and physics, especially in trigonometry and coordinate systems. They provide a direct relationship between the angle and the arc length. When working with these problems:
- **Defining Radians:** One radian corresponds to an angle whose arc length is equal to the radius of the circle. The complete circle measures \(2\pi\) radians.
- **Conversions:** Commonly needed when converting degrees to radians (e.g., 180° equals \(\pi\) radians).
- **In Practice:** In this exercise, recognizing \(\frac{\pi}{2}\) signifies a 90° turn, and \(\frac{\pi}{4}\) corresponds to a 45° angle can illuminate understanding.