Chapter 23: Problem 50
A point charge \(q\) and a charge \((-q)\) are placed at \(x=-a\) and \(x=+a\) respectively. Which of the following represents a part of \(E-x\) graph ?
Short Answer
Expert verified
The graph of \( E \) vs \( x \) is anti-symmetric about the origin, with zero at \( x = 0 \).
Step by step solution
01
Understanding the Problem
We have two point charges: charge \( q \) at position \( x = -a \) and charge \( -q \) at position \( x = +a \). We need to represent the electric field \( E \) as a function of position \( x \) on a graph.
02
Considering Symmetry and Direction
The electric field due to a positive charge \( q \) points away from the charge, while the field due to a negative charge \( -q \) points towards the charge. Because of symmetry and opposite charges, the field will be symmetrically opposite across the y-axis with zero potential at \( x=0 \).
03
Finding Electric Field at Different Regions
1. For \( x < -a \), the field \( E \) is predominantly influenced by charge \( q \) at \( x = -a \) and points left.2. For \( -a < x < a \), between the charges, fields from \( q \) and \( -q \) add because they point in opposite directions towards each other.3. For \( x > a \), the field is predominantly influenced by charge \( -q \) at \( x = +a \) and points right.
04
Determining Electric Field Strengths
The electric field due to a point charge is given by \( E = \frac{kq}{r^2} \). So:- For \( x < -a \), the field is negative and strong.- At \( x = 0 \), \( E = 0 \) due to the cancellation of the fields.- For \( x > a \), the field is positive but weaker with increasing \( x \).
05
Analyzing the Graph Shape
The graph of the electric field \( E \) vs \( x \) will show:- Negative values for \( x < -a \), decreasing with decreasing \( x \).- A zero crossing at \( x = 0 \). - Positive values for \( x > a \), decreasing as \( x \) increases.The graph should be anti-symmetric around the origin.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Point Charge
A point charge is a fundamental concept in electromagnetism describing a charge located at a single point in space. This is an idealization that helps simplify calculations of electric fields.
- Point charges can be either positive or negative. A positive charge causes electric fields that point away from the charge, while a negative charge attracts electric field lines towards itself.
- The magnitude of the electric field \'E\' produced by a point charge diminishes with the square of the distance from the charge, based on Coulomb's Law: \( E = \frac{kq}{r^2} \), where \( k \) is Coulomb's constant, \( q \) is the magnitude of the charge, and \( r \) is the distance from the charge to the point of interest.
Symmetry in Electric Fields
Symmetry plays a crucial role in understanding and visualizing electric fields created by multiple charges. In the given scenario, we have two equal yet opposite charges positioned symmetrically at \( x = -a \) and \( x = +a \).
- Due to this symmetry and the nature of electric fields from positive and negative charges, the resulting electric field configuration is symmetric about the y-axis.
- At the midpoint between the two charges (\( x=0 \)), the electric fields from each charge exactly cancel out, yielding a net electric field of zero.
Electric Field Strength
Electric field strength is a measure of the force experienced per unit charge in an electric field. The formula \( E = \frac{kq}{r^2} \) operates as a cornerstone to calculate the strength at specific positions.
- For \( x < -a \), the electric field is dominated by the charge at \( x = -a \). Its influence weakens as we move farther left away from the charge.
- Within the region \( -a < x < a \), electric fields from both charges overlap. These fields add up since they point in opposite directions towards each other, forming a strong field.
- Past \( x = +a \), the influence of the negative charge at \( x = +a \) prevails. Here, the field strength decreases with increasing \( x \) distance from the charge.