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The armature of a small generator consists of a flat, square coil with 120 turns and sides with a length of \(1.60 \mathrm{~cm} .\) The coil rotates in a magnetic field of \(0.0750 \mathrm{~T}\). What is the angular speed of the coil if the maximum emf produced is \(24.0 \mathrm{mV} ?\)

Short Answer

Expert verified
The angular speed of the coil is therefore approximately \( 1.25 \times 10^{8} rad/s \) .

Step by step solution

01

Understand the relationship between induced emf and magnetic flux

Use the Faraday's law formula to understand that the induced emf (voltage) \( \epsilon \) is equal to the rate of change of magnetic flux \( \Phi \). The formula is given as: \( \epsilon = -N \frac{\delta \Phi}{\delta t} \) where N is the number of turns in the coil.
02

Find the formula for max emf

Determine that the max emf \( \epsilon_{max} \) is given as: \( \epsilon_{max} = NBA\omega \) , where B is the magnetic field, A is the area (for a square coil A = \( side^2 \)), and ω is the angular speed we want to find.
03

Substitute the known values

Keep the desired variable ω on one side and substitute every other known values. The equation will look like this: \( \omega = \frac{\epsilon_{max}}{NBA} \).
04

Calculate for ω

After substituting the known values, calculate for ω. Your equation will be, \( \omega = \frac{24.0 \times 10^{-3}}{120 \times 0.0750 \times (0.0160)^2} \) .
05

Provide Final Answer

Calculate the value to find the angular speed.

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Key Concepts

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

Faraday's Law of Induction
Faraday's Law of Induction is a fundamental principle that explains how electric voltage is generated within a circuit by a varying magnetic field. This law is pivotal in the functioning of numerous electrical devices like transformers and generators. Faraday's Law states that the induced electromotive force (emf) in any closed circuit is equal to the negative of the rate of change of the magnetic flux through the circuit. In mathematical terms, it is expressed as:
  • \( \epsilon = -N \frac{\delta \Phi}{\delta t} \)
Here, \( \epsilon \) represents the induced emf, \( N \) is the number of turns in the coil, and \( \frac{\delta \Phi}{\delta t} \) is the rate of change of magnetic flux. The negative sign in the formula indicates Lenz's law, which states that the induced emf will always act to oppose the change in flux.
Faraday's law is crucial for understanding how electric generators work, as these devices operate by rotating coils within magnetic fields to induce voltage. The quicker or more intensely a magnetic field changes, the greater the induced voltage.
Magnetic Flux
Magnetic Flux is a measure of the total magnetic field passing through a given area, typically framed in terms of the number of magnetic field lines crossing the area. It’s denoted by the symbol \( \Phi \) and is calculated using the formula:
  • \( \Phi = B \cdot A \cdot \cos\theta \)
In this formula, \( B \) represents the magnetic field strength, \( A \) is the area through which the field lines pass, and \( \theta \) is the angle between the field lines and the normal (perpendicular) to the surface area.
In the context of generators, the coil's rotation continuously changes the angle \( \theta \), resulting in changes in magnetic flux and subsequently inducing an emf according to Faraday’s Law.
The concept of magnetic flux helps us comprehend how changes in the orientation or size of a coil can impact the emf and the efficiency of energy conversion in devices like generators.
Angular Speed
Angular Speed is an important concept in rotational motion, representing how fast an object rotates about a particular axis. It is denoted by the symbol \( \omega \) and is typically expressed in radians per second. For a generator, the angular speed refers to how quickly the coil spins within the magnetic field.
Angular speed is linked to the induced emf through the equation:
  • \( \epsilon_{max} = NBA\omega \)
Here, \( \epsilon_{max} \) is the maximum emf produced, \( N \) is the number of turns in the coil, \( B \) is the magnetic field, \( A \) is the area of the coil, and \( \omega \) is the angular speed.
In the problem at hand, knowing the angular speed helps predict the voltage output of the generator. By manipulating the coil’s angular velocity, we can control the generator’s performance, vital for meeting specific power demands.

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