Chapter 15: Problem 6
Sketch the vector field by drawing some representative nonintersecting vectors. The vectors need not be drawn to scale, but they should be in reasonably correct proportion relative to each other.\(\mathbf{F}(x, y)=y \mathbf{j}, \quad y>0\)
Short Answer
Expert verified
Vectors point upward, increasing in magnitude with \( y \), for \( y>0 \).
Step by step solution
01
Understand the Vector Field Components
The vector field is given by \( \mathbf{F}(x, y)=y \mathbf{j} \). Here, \( \mathbf{j} \) is the unit vector in the direction of the positive \( y \)-axis. This means that the vector field has no \( i \)-component (no horizontal component). The magnitude and direction of each vector depends only on the \( y \)-value and it points upwards because of the positive \( \mathbf{j} \) component. For \( y > 0 \), the vectors will always have a positive magnitude.
02
Determine the Vector Magnitudes
For any point \((x, y)\), the vector has the form \( \mathbf{F}(x, y) = y \mathbf{j} \). This means at any point \((x, y)\), the magnitude of the vector is simply \( y \). So, as \( y \) increases, the length of the vector increases. When \( y = 1 \), the vector's length is 1; when \( y = 2 \), the vector's length is 2, and so on.
03
Sketch the Vector Field
To sketch this vector field, draw vectors originating at several points in the plane where \( y > 0 \). For example, choose points where \( y = 1, 2, 3, \ldots \). At each chosen point \((x, y)\), draw a vector pointing directly upwards (along the positive \( y \)-axis) with a length proportional to \( y \). For \( y=1 \), draw short vectors at points like \((0, 1), (1, 1),\) etc. For \( y=2 \), draw longer vectors at points like \((0, 2), (1, 2),\) etc. Ensure that vectors do not intersect, and the pattern shows increasing length as \( y \) increases.
04
Analyze the Sketch for Accuracy
Check the sketch to verify that vectors are aligned along the positive \( y \)-axis with increasing length as \( y \) increases. Make sure the overall pattern shows an array of upward-pointing vectors that convey the sense of flow in the direction of increasing \( y \), confirming that the vector field is consistent with the formula \( \mathbf{F}(x, y) = y \mathbf{j} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vector Magnitude
In a vector field, the magnitude of a vector provides an understanding of its strength or size at a given point. For the vector field \( \mathbf{F}(x, y) = y \mathbf{j} \),the magnitude is dictated solely by the \( y \)-component. The formula shows that each vector's magnitude is equal to the value of \( y \).
To comprehend this, consider these key points:
To comprehend this, consider these key points:
- When \( y = 1 \), the magnitude of the vector is 1, representing a basic unit length in the vector field.
- As \( y \) increases, the magnitude of the vector directly proportionally increases. For instance, if \( y = 3 \), the magnitude becomes 3, making the vector three times longer than when \( y = 1 \).
- This linear relationship between the vector magnitude and the \( y \)-value results in vectors lengthening as they move upwards in the plane.
Sketching Vectors
Sketching vectors begins with recognizing how length and direction are displayed. For \( \mathbf{F}(x, y) = y \mathbf{j} \),all vectors point upwards because the direction is determined by \( \mathbf{j} \), which is along the positive \( y \)-axis.
Here's how to effectively sketch vectors:
Here's how to effectively sketch vectors:
- Start by selecting several points where \( y > 0 \); points such as \( (0, 1), (1, 1), (0, 2), (1, 2) \) work well.
- Draw arrows originating from these points; their length should represent the \( y \)-value of the point.
- Keep vectors non-intersecting and proportional to each other to maintain clarity in the sketch.
Coordinate System
A coordinate system serves as the backdrop when sketching vector fields. In our given exercise, the coordinate system uses the Cartesian plane, consisting of the \( x \)-axis (horizontal) and \( y \)-axis (vertical).
Understanding this system is crucial for accurately representing vectors:
Understanding this system is crucial for accurately representing vectors:
- The Cartesian coordinate system allows us to locate points precisely, expressed as \((x, y)\).
- In the vector field \( \mathbf{F}(x, y) = y \mathbf{j} \),vectors are constructed at coordinates where \( y \) is positive.
- Vectors have no horizontal component, making the \( x \)-coordinate flexible without affecting the vector's magnitude or direction.