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\(\bullet\) (a) What must the charge (sign and magnitude) of a 1.45 \(\mathrm{g}\) particle be for it to remain balanced against gravity when placed in a downward-directed electric field of magnitude 650 \(\mathrm{N} / \mathrm{C}^{?}\) (b) What is the magnitude of an electric field in which the electric force it exerts on a proton is equal in magni- tude to the proton's weight?

Short Answer

Expert verified
(a) Charge is \(-2.186 \times 10^{-5} \ C\); (b) Electric field is \(1.025 \times 10^{-7} \ N/C\).

Step by step solution

01

Understand the Forces

For the particle to remain balanced against gravity, the electric force acting on it must be equal and opposite to the gravitational force. The gravitational force can be calculated using the formula \( F_g = mg \), where \( m \) is the mass and \( g \) is the acceleration due to gravity \( (9.8 \ m/s^2) \).
02

Calculate the Gravitational Force

Given the mass of the particle \( m = 1.45 \ g \) \( (0.00145 \ kg) \), the gravitational force \( F_g = 0.00145 \times 9.8 = 0.01421 \ N \).
03

Apply Electric Force Equation

The electric force \( F_e \) can be calculated with \( F_e = qE \) where \( q \) is the charge on the particle and \( E = 650 \ N/C \) is the electric field. Since \( F_e = F_g \), we can set \( qE = mg \).
04

Solve for Charge

Rearrange the equation to solve for \( q \):\[ q = \frac{mg}{E} = \frac{0.01421}{650} = 2.186 \times 10^{-5} \ C \]. The charge must be negative because the electric field is downward-directed and should balance the upward gravitational force.
05

Calculate Proton Weight

The weight of a proton is given by \( F_g = mg \), with the mass of the proton \( m = 1.67 \times 10^{-27} \ kg \). Thus, \( F_g = 1.67 \times 10^{-27} \times 9.8 = 1.64 \times 10^{-26} \ N \).
06

Determine Electric Field for Proton

The electric force on the proton should equal its weight, so \( q_pE = 1.64 \times 10^{-26} \ N \), where \( q_p = 1.6 \times 10^{-19} \ C \). Solving for \( E \):\[ E = \frac{1.64 \times 10^{-26}}{1.6 \times 10^{-19}} = 1.025 \times 10^{-7} \ N/C \].

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Key Concepts

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

Gravitational Force
Gravitational force is a fundamental concept in physics. It is the force exerted by the Earth's gravity on any object with mass. To calculate this force, we use the formula:
  • \( F_g = mg \)
In this equation, \( F_g \) represents the gravitational force, \( m \) stands for the mass of the object, and \( g \) denotes the acceleration due to gravity, which is approximately \( 9.8 \, \text{m/s}^2 \) on the surface of the Earth. Whenever you have an object with mass, gravity pulls it towards the Earth's center with a force that depends directly on its mass. The more massive the object, the stronger the pull.
Understanding gravitational force is essential in balancing other forces, like the electric force, as seen in many physics problems. This balance is crucial in cases where an object needs to stay suspended or neutralized between forces acting on it.
Charge Calculation
Charge calculation involves determining the amount of electric charge needed to balance forces acting on an object in an electric field. When a charged particle is subjected to an electric field, it experiences an electric force. To find the charge \( q \) necessary for balancing a gravitational force, use the formula:
  • \( F_e = qE \)
  • \( q = \frac{mg}{E} \)
Here, \( F_e \) represents the electric force equal to the gravitational force \( F_g \). \( q \) stands for the charge, and \( E \) is the electric field strength. The calculation becomes straightforward: you solve for \( q \) by dividing the gravitational force by the electric field's magnitude. In the original exercise, they calculated the charge needed to counterbalance gravity in a 650 N/C electric field, resulting in a specific charge value.
Remember, in the scenario where the electric field has a direction, the necessary charge needs to have the opposite sign to ensure balance. In downward electric fields, like those mentioned, a negative charge ensures an upward electric force.
Electric Field
The electric field is an invisible field around charged particles that exerts a force on other charges within the field. It is essential in determining how much force a charge will experience. The formula to calculate the force experienced by a charge in an electric field is:
  • \( F_e = qE \)
Where \( F_e \) is the electric force, \( q \) the charge, and \( E \) the electric field strength. Understanding electric fields is critical in physics since these fields naturally arise wherever charges exist.
Moreover, in the original exercise, they calculated the electric field strength required to make the electric force on a proton equal its gravitational force. By using the known charge of a proton \( (1.6 \times 10^{-19} \, C) \) and its gravitational force, the electric field strength was determined easily.
The balance of electric force with gravitational force highlights how electric fields can be manipulated to counterbalance different forces acting on charged particles.

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Most popular questions from this chapter

\(\bullet$$\bullet\) A \(9.60-\mu \mathrm{C}\) point charge is at the center of a cube with sides of length 0.500 \(\mathrm{m}\) . (a) What is the electric flux through one of the six faces of the cube? (b) How would your answer to part (a) change if the sides were 0.250 m long? Explain.

\(\bullet\) (a) A closed surface encloses a net charge of 2.50\(\mu \mathrm{C}\) . What is the net electric flux through the surface? (b) If the electric flux through a closed surface is determined to be \(1.40 \mathrm{N} \cdot \mathrm{m}^{2} / \mathrm{C},\) how much charge is enclosed by the surface?

\(\bullet\) Signal propagation in neurons. Neurons are components of the nervous system of the body that transmit signals as elec- trical impulses travel along their length. These impulses propa- gate when charge suddenly rushes into and then out of a part of the neutron called an axon. Measurements have shown that, during the inflow part of this cycle, approximately \(5.6 \times 10^{11} \mathrm{Na}^{+}\) (sodium ions) per meter, each with charge \(+e\) enter the axon. How many coulombs of charge enter a 1.5 \(\mathrm{cm}\) length of the axon during this process?

\(\bullet$$\bullet\) An electron is released from rest in a uniform electric field. The electron accelerates vertically upward, traveling 4.50 \(\mathrm{m}\) in the first 3.00\(\mu\) s after it is released. (a) What are the magnitude and direction of the electric field? (b) Are we justified in ignor- ing the effects of gravity? Justify your answer quantitatively.

\(\bullet\)(a) How many excess elec- trons must be distributed uni- formly within the volume of an isolated plastic sphere 30.0 \(\mathrm{cm}\) in diameter to produce an elec- tric field of 1150 \(\mathrm{N} / \mathrm{C}\) just out- side the surface of the sphere? (b) What is the electric field at a point 10.0 cm outside the surface of the sphere?

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