Chapter 24: Problem 29
A point charge of \(-3.0 \times 10^{-5} \mathrm{C}\) is placed at the origin of coordinates in vacuum. Find the electric field at the point \(x=5.0 \mathrm{~m}\) on the \(x\) -axis.
Short Answer
Expert verified
The electric field at \( x=5.0 \: \text{m} \) is \( 1.0788 \times 10^4 \: \text{N/C} \), directed towards the origin.
Step by step solution
01
Understand the Formula for Electric Field
The electric field \( E \) created by a point charge \( q \) at a distance \( r \) is given by the formula: \[ E = \frac{k \cdot |q|}{r^2} \] where \( k \) is Coulomb's constant, \( k = 8.99 \times 10^9 \: \text{N}\cdot\text{m}^2/\text{C}^2 \).
02
Identify the Given Values
We know that the charge \( q = -3.0 \times 10^{-5} \: \text{C} \) and the distance \( r = 5.0 \: \text{m} \) on the \( x \)-axis from the charge.
03
Substitute Values Into the Formula
Substitute the known values into the electric field formula: \[ E = \frac{8.99 \times 10^9 \times | -3.0 \times 10^{-5} |}{(5.0)^2} \]
04
Calculate the Electric Field Magnitude
First calculate the magnitude of the charge: \( |-3.0 \times 10^{-5}| = 3.0 \times 10^{-5} \). The expression becomes \[ E = \frac{8.99 \times 10^9 \times 3.0 \times 10^{-5}}{25} \]. Calculate \( E \): \[ E = \frac{2.697 \times 10^5}{25} = 1.0788 \times 10^4 \: \text{N/C} \].
05
Determine the Direction of the Electric Field
Since the charge is negative, the direction of the electric field is towards the charge. Since we are considering the point \( x = 5.0 \: \text{m} \) on the \( x \)-axis, the electric field will point towards the origin where the negative charge is located.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Coulomb's constant
Coulomb's constant, often denoted by the symbol \( k \), is a fundamental constant in physics that plays a crucial role in the calculation of electric fields due to point charges. It is a measure of the strength of the electric force between two charges separated by a certain distance. In the context of a vacuum, Coulomb's constant has a value of \( 8.99 \times 10^9 \, \text{N} \cdot \text{m}^2/\text{C}^2 \). This constant allows us to understand how forces are transmitted through space by the electric field.
- Importance in Electrostatics: Coulomb's constant is critical because it quantifies the level of interaction between charged objects.
- Relation to the Permittivity of Free Space: It is inversely related to the permittivity of free space \( \varepsilon_0 \), defined by \( k = \frac{1}{4\pi \varepsilon_0} \).
Point Charge
A point charge is a concept in electrostatics representing an electric charge that is assumed to be located at a single point in space. This simplification makes it easier to apply mathematical formulas to calculate the electric fields and forces.
- Simplification: Although actual charges have a spatial distribution, they can often be treated as point charges when their size is negligible compared to other dimensions involved in the problem.
- Applications: Point charges are a fundamental part of many physics problems, helping to simplify complex systems where charge distribution is not uniform.
Electric Field Direction
The direction of an electric field is a crucial part of understanding how electric forces act. The electric field direction indicates where a positive test charge placed in the field would move due to the force exerted by the field.
- Positive vs Negative Charges: For a positive point charge, the electric field radiates outwards, while for a negative point charge, it converges inwards towards the charge.
- Understanding the Context: In our specific exercise, we have a negative point charge, so the electric field at any given point, like \( x = 5.0 \, \text{m} \), is directed towards the charge itself because it attracts positive charges.