/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 14 A small object of mass \(m\) car... [FREE SOLUTION] | 91Ó°ÊÓ

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A small object of mass \(m\) carries a charge \(q\) and is suspended by a thread between the vertical plates of a parallel-plate capacitor. The plate separation is \(d\). If the thread makes an angle \(\theta\) with the vertical, what is the potential difference between the plates?

Short Answer

Expert verified
The potential difference between the plates of the capacitor is \(V = d*mg*\tan{\theta}/q\).

Step by step solution

01

Identifying the forces

There are three forces acting on this charged object. The gravitational force (\(mg\) downwards), the tension force in the thread (along the thread) and the force due to the electric field (\(E*q\), upwards). The electric force and the gravitational force are vertical, whereas the tension force is at an angle.
02

Resolving the tension force and formulating the equations

As the thread is inclined at an angle \(\theta\) with the vertical, the horizontal component of tension balances the electrical force and the vertical component balances the gravitational force. So we write the equations: \( T\sin{\theta}= Eq \) and \( T\cos{\theta}= mg \). Dividing the first equation by the second gives: \(\tan{\theta}= \frac{Eq}{mg}\). This gives us the electric field intensity as \(E= mg\tan{\theta}/q\). The electric field intensity between the plates of a capacitor is also given by \(E=V/d\), where \(V\) is the potential difference between the plates.
03

Calculating the potential difference

Substituting the expression for \(E\) from step 2 into the equation \(E=V/d\) and rearranging terms, we find the potential difference \(V = d*mg*\tan{\theta}/q\).

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Key Concepts

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

Electric Force in Capacitors
Electric force is a fundamental aspect of understanding how capacitors function. Within a parallel-plate capacitor, electric force acts on any charge present in the electric field between the plates. The strength of this force is directly proportional to both the amount of charge on the object and the strength of the electric field, mathematically represented as \( F = Eq \), where \( F \) is the electric force, \( E \) is the electric field intensity, and \( q \) is the charge of the object.

In the case of the exercise, a charged object experiences electric force in an upward direction, which is counteracted by the downward gravitational force. This interaction not only helps determine the object's equilibrium but also provides insight into the potential difference across the plates, as the electric force plays a crucial role in establishing the balance of forces.
Potential Difference Calculation
The potential difference, or voltage, between the plates of the capacitor is a measurement of the energy required to move a charge within an electric field. Calculating this value involves understanding the relationship between the electric field and the distance between the plates. The formula \( V = Ed \) defines this relationship, where \( V \) is the potential difference, \( E \) is the electric field intensity, and \( d \) is the separation between the plates.

In the provided exercise, the potential difference calculation is vital for understanding the energy interaction and can be determined using the equation that relates the electric force, mass of the object, gravitational acceleration, and charge. The final formula derived in the step-by-step solution is an excellent example of the practical application of this concept, \( V = d \cdot mg \cdot \tan{\theta} / q \), enhancing the educational value by showing how separate physical principles interconnect.
Electric Field Intensity
The concept of electric field intensity is central in understanding how charged particles react in an electric field. It essentially quantifies the strength of an electric field at a given point. For parallel-plate capacitors, the field is uniform and directed from the positive to the negative plate. Its magnitude can be described by \( E = V/d \), where \( E \) is the electric field intensity, \( V \) is the potential difference, and \( d \) is the distance between the plates.

It is essential to grasp that electric field intensity is uniform across a parallel-plate capacitor, which simplifies calculations and analyses. In the given exercise, using the equilibrium condition of the forces at an angle, we've derived an expression for the electric field in terms of physical quantities such as mass, gravitational acceleration, angle, and charge. This underscores the interconnectedness of electric fields with other physical quantities and forces.
Capacitor Charge Relationship
Understanding the relationship between the charge on a capacitor and other electrical properties is crucial for grasping the behavior of capacitors in circuits. This relationship is exemplified in the formula \( Q = CV \), where \( Q \) is the charge stored on the capacitor, \( C \) is the capacitance, and \( V \) is the potential difference across the capacitor's plates.

While the original exercise focuses on potential difference, it's pertinent to highlight that the charge on the plates determines the stored electrical energy in the capacitor. As an educator, it is essential to emphasize this relationship, as it aids students in understanding why, for example, capacitors with larger plate areas or smaller plate separations have a higher capacitance and can store more charge for a given potential difference. The ability of capacitors to store charge is a foundational concept that plays a significant role in a wide range of applications from simple circuit design to complex electronic devices.

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Most popular questions from this chapter

According to its design specification, the timer circuit delaying the closing of an elevator door is to have a capacitance of \(32.0 \mu \mathrm{F}\) between two points \(A\) and \(B .\) (a) When one circuit is being constructed, the inexpensive but durable capacitor installed between these two points is found to have capacitance \(34.8 \mu \mathrm{F}\). To meet the specification, one additional capacitor can be placed between the two points. Should it be in series or in parallel with the \(34.8-\mu \mathrm{F}\) capacitor? What should be its capacitance? (b) What If? The next circuit comes down the assembly line with capacitance \(29.8 \mu \mathrm{F}\) between \(A\) and \(B .\) What additional capacitor should be installed in series or in parallel in that circuit, to meet the specification?

Find the capacitance of the Earth. (Suggestion: The outer conductor of the "spherical capacitor" may be considered as a conducting sphere at infinity where \(V\) approaches zero.)

Two capacitors, \(C_{1}=5.00 \mu \mathrm{F}\) and \(C_{2}=12.0 \mu \mathrm{F},\) are connected in parallel, and the resulting combination is connected to a \(9.00-\mathrm{V}\) battery. (a) What is the equivalent capacitance of the combination? What are (b) the potential difference across each capacitor and (c) the charge stored on each capacitor?

Two identical parallel-plate capacitors, each with capacitance \(C,\) are charged to potential difference \(\Delta V\) and connected in parallel. Then the plate separation in one of the capacitors is doubled. (a) Find the total energy of the system of two capacitors before the plate separation is doubled. (b) Find the potential difference across each capacitor after the plate separation is doubled. (c) Find the total energy of the system after the plate separation is doubled. (d) Reconcile the difference in the answers to parts (a) and (c) with the law of conservation of energy.

Review problem. A certain storm cloud has a potential of \(1.00 \times 10^{8} \mathrm{V}\) relative to a tree. If, during a lightning storm, \(50.0 \mathrm{C}\) of charge is transferred through this potential difference and \(1.00 \%\) of the energy is absorbed by the tree, how much sap in the tree can be boiled away? Model the sap as water initially at \(30.0^{\circ} \mathrm{C}\). Water has a specific heat of \(4186 \mathrm{J} / \mathrm{kg}^{\circ} \mathrm{C},\) a boiling point of \(100^{\circ} \mathrm{C},\) and a latent heat of vaporization of \(2.26 \times 10^{6} \mathrm{J} / \mathrm{kg}\).

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