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In a certain region of space, the electric potential is \(V(x, y, z) = Axy - Bx^2 + Cy,\) where \(A, B,\) and \(C\) are positive constants. (a) Calculate the \(x\)-, \(y\)-, and \(z\)-components of the electric field. (b) At which points is the electric field equal to zero?

Short Answer

Expert verified
The electric field components are \((2Bx - Ay, -Ax - C, 0)\); the field is zero where \(2Bx = Ay\) and \(-Ax = C\).

Step by step solution

01

Understanding the Problem

The electric potential given is a function of coordinates \(x\), \(y\), and \(z\) as \(V(x, y, z) = Axy - Bx^2 + Cy\). We need to find the components of the electric field, which are derived from the negative gradient of the potential.
02

Calculating the Electric Field Components

The electric field \(\mathbf{E}\) is the negative gradient of the potential, \(V(x, y, z)\).Calculate \(E_x = -\frac{\partial V}{\partial x} = -\frac{\partial}{\partial x}(Axy - Bx^2 + Cy) = -(Ay - 2Bx) = 2Bx - Ay\).Calculate \(E_y = -\frac{\partial V}{\partial y} = -\frac{\partial}{\partial y}(Axy - Bx^2 + Cy) = -Ax - C\).Calculate \(E_z = -\frac{\partial V}{\partial z} = 0\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Electric Potential
Electric potential, often denoted by the symbol \( V \), is a fundamental concept in electromagnetism and physics. It represents the amount of electric potential energy per unit charge at a point in a field. This is similar to the concept of gravitational potential energy in a gravitational field.

In simpler terms, the electric potential tells us about the 'energy landscape.' When a positive charge moves in an electric field, it tends to move from regions of higher potential to regions of lower potential, similarly to how an object in a gravitational field moves downhill.

For the given exercise, the electric potential function is expressed as \( V(x, y, z) = Axy - Bx^2 + Cy \). Here, the terms involve coordinates \( x \), \( y \), and \( z \), describing how potential changes in space.
  • \( Axy \): This term introduces a variation of potential depending on the product of \( x \) and \( y \).
  • \( -Bx^2 \): This term introduces a parabolic change along the \( x \)-axis.
  • \( Cy \): A linear variation along the \( y \)-axis.
Understanding how potential varies helps us calculate related electric field values.
Gradient
The concept of the gradient is crucial in vector calculus, especially when dealing with scalar fields like electric potential.

The gradient of a function gives us a vector that points in the direction of the greatest rate of increase of the function. When applied to electric potential, it tells us how the potential changes as we move from one point to another in space.

Mathematically, if \( V \) is an electric potential, the gradient \( abla V \) points towards the maximum increase of \( V \). However, the electric field \( \mathbf{E} \) is the opposite direction, described by the negative gradient, \( \mathbf{E} = -abla V \).
  • It highlights where the electric force would move a positive charge.
  • It is calculated using partial derivatives with respect to each coordinate axis.
In the exercise solution, we compute for each axis:\[ E_x = -\frac{\partial V}{\partial x} \] \[ E_y = -\frac{\partial V}{\partial y} \] \[ E_z = -\frac{\partial V}{\partial z} \] Therefore, the gradient provides us the information needed for determining the directional force components.
Vector Calculus
Vector calculus is a powerful tool in physics and engineering for analyzing vector fields. It combines both differential and integral calculus to study vector functions.

In this exercise, vector calculus helps us relate electric potential, a scalar field, to the electric field, a vector field. We use tools like partial differentiation to find how quantities change in space.

The electric field \( \mathbf{E} \) can be seen as a result of combining various partial derivatives of the electric potential \( V \) with respect to \( x \), \( y \), and \( z \).
  • The field \( E_x \) is derived using \(-\frac{\partial V}{\partial x} \).
  • The field \( E_y \) is derived using \(-\frac{\partial V}{\partial y} \).
  • The field \( E_z \) is derived using \(-\frac{\partial V}{\partial z} \).
By using vector calculus, you can see how slight changes in position lead to variations in the electric field. This lets you determine forces and movements under electric influence.
Physics Problem Solving
Being able to tackle physics problems requires a strategic approach and understanding fundamental principles.

For the given exercise, we solve tasks by finding the relationship between electric potential and electric field components. The problem-solving process involves a combination of conceptual understanding and mathematical technique.

Here's how to approach these problems effectively:
  • Understand the Problem: Provide a clear statement of what the problem asks, just like identifying the electric potential function in the exercise.
  • Identify Known and Unknowns: Note known values (such as constants \( A, B, \) and \( C \)) and what you're solving for (electric field components).
  • Apply Relevant Principles: Use relevant physics principles; in this case, the concept of the negative gradient of electric potential.
  • Solve Step-by-Step: Break down complex calculations into smaller parts to make them manageable, as demonstrated in the solution's steps.
Employing a structured method aids in solving complex problems efficiently and accurately, enhancing both comprehension and retention of physical principles.

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Most popular questions from this chapter

Three equal 1.20-\(\mu$$C\) point charges are placed at the corners of an equilateral triangle with sides 0.400 m long. What is the potential energy of the system? (Take as zero the potential energy of the three charges when they are infinitely far apart.)

When radium-226 decays radioactively, it emits an alpha particle (the nucleus of helium), and the end product is radon-222. We can model this decay by thinking of the radium-226 as consisting of an alpha particle emitted from the surface of the spherically symmetric radon-222 nucleus, and we can treat the alpha particle as a point charge. The energy of the alpha particle has been measured in the laboratory and has been found to be 4.79 MeV when the alpha particle is essentially infinitely far from the nucleus. Since radon is much heavier than the alpha particle, we can assume that there is no appreciable recoil of the radon after the decay. The radon nucleus contains 86 protons, while the alpha particle has 2 protons and the radium nucleus has 88 protons. (a) What was the electric potential energy of the alpha\(-\)radon combination just before the decay, in MeV and in joules? (b) Use your result from part (a) to calculate the radius of the radon nucleus.

At a certain distance from a point charge, the potential and electric-field magnitude due to that charge are 4.98 V and 16.2 V\(/\)m, respectively. (Take \(V = 0\) at infinity.) (a) What is the distance to the point charge? (b) What is the magnitude of the charge? (c) Is the electric field directed toward or away from the point charge?

A uniform electric field has magnitude \(E\) and is directed in the negative \(x\)-direction. The potential difference between point \(a\) (at \(x =\) 0.60 m) and point \(b\) (at \(x =\) 0.90 m) is 240 V. (a) Which point, \(a\) or \(b\), is at the higher potential? (b) Calculate the value of \(E\). (c) A negative point charge \(q = -\)0.200 \(\mu\)C is moved from \(b\) to \(a\). Calculate the work done on the point charge by the electric field.

A thin spherical shell with radius \(R_1 =\) 3.00 cm is concentric with a larger thin spherical shell with radius \(R_2 =\) 5.00 cm. Both shells are made of insulating material. The smaller shell has charge \(q_1 = +\)6.00 nC distributed uniformly over its surface, and the larger shell has charge \(q_2 = -\)9.00 nC distributed uniformly over its surface. Take the electric potential to be zero at an infinite distance from both shells. (a) What is the electric potential due to the two shells at the following distance from their common center: (i) \(r =\) 0; (ii) \(r =\) 4.00 cm; (iii) \(r =\) 6.00 cm? (b) What is the magnitude of the potential difference between the surfaces of the two shells? Which shell is at higher potential: the inner shell or the outer shell?

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