/*! 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 28 A circular coil of radius \(8.0 ... [FREE SOLUTION] | 91Ó°ÊÓ

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A circular coil of radius \(8.0 \mathrm{~cm}\) and 20 turns is rotated about its vertical diameter with an angular speed of \(50 \mathrm{rad} / \mathrm{s}\) in a uniform horizontal magnetic field of magnitude \(3.0 \times 10^{-2} \mathrm{~T}\). Obtain the maximum and average emf induced in the coil. If the coil forms a closed-loop of resistance \(10 \Omega\), calculate the maximum value of current in the coil. Calculate the average power loss due to Joule heating. [NCERT] (a) \(2 \mathrm{~W}\) (b) \(0.2 \mathrm{~W}\) [c) \(0.49 \mathrm{~W}\) (d) \(0.018 \mathrm{~W}\)

Short Answer

Expert verified
Maximum emf is 0.60 V; average emf is 0 V; max current is 0.06 A; power loss is 0.018 W.

Step by step solution

01

Understanding the Problem

The exercise involves calculating the maximum and average induced emf in a rotating coil, as well as the maximum current and power loss due to resistance. The coil rotates in a magnetic field, so Faraday's law of electromagnetic induction will be applied.
02

Calculate Maximum Induced emf

The formula for the maximum emf (\( \varepsilon_{max} \)) induced in a coil is \( \varepsilon_{max} = NAB\omega \). Given \( N = 20 \) turns, \( A = \pi r^2 = \pi (0.08 \text{ m})^2 \), \( B = 3.0 \times 10^{-2} \text{ T} \), and \( \omega = 50 \text{ rad/s} \), calculate \( \varepsilon_{max} \).\[A = \pi \times (0.08)^2 = 0.020106 \text{ m}^2\]\[ \varepsilon_{max} = 20 \times 0.020106 \times 3.0 \times 10^{-2} \times 50 = 0.60 \text{ V} \]
03

Determine Average Emf

The average emf over one complete rotation is zero because it is a sinusoidal waveform and averages out over a cycle. The average emf, in this case, is zero \( \varepsilon_{avg} = 0 \).
04

Calculate Maximum Current in Coil

Using Ohm's Law, the maximum current \( I_{max} \) can be found using \( \varepsilon_{max} \) and resistance \( R = 10 \Omega \):\[ I_{max} = \frac{\varepsilon_{max}}{R} = \frac{0.60}{10} = 0.06 \text{ A} \]
05

Calculate Average Power Loss due to Joule Heating

The average power loss \( P \) due to resistance in a coil is calculated using the equation \( P = \frac{1}{2} \varepsilon_{max} I_{max} \):\[P = \frac{1}{2} \times 0.60 \times 0.06 = 0.018 \text{ W}\]Thus, the average power loss due to Joule heating is \( 0.018 \text{ W} \).

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Key Concepts

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

Faraday's Law
Faraday's Law of electromagnetic induction is a fundamental principle that describes how an electric field is generated by a changing magnetic field. This law states that the induced electromotive force (emf) in any closed circuit is equal to the rate of change of the magnetic flux through the circuit. In mathematical terms, Faraday's Law can be expressed as:
\[ ext{emf} = -N \frac{d ext{Φ}_m}{dt} \]where:
  • \( N \): Number of turns in the coil
  • \( ext{Φ}_m \): Magnetic flux
  • \( \frac{d ext{Φ}_m}{dt} \): Rate of change of magnetic flux
In our exercise, Faraday's Law is used to calculate the maximum induced emf when the coil rotates at a certain speed in the magnetic field. The formula simplifies to \( ext{emf} = NAB\omega \) for a coil rotating uniformly, where:
  • \( A \): Area of the coil, obtained from its radius
  • \( B \): Magnetic field strength
  • \( \omega \): Angular speed of rotation
By applying these principles correctly, we find that a maximum emf of 0.60 V is induced in the coil.
Joule Heating
Joule Heating, also known as resistive or ohmic heating, refers to the process where the electric current passing through a conductor produces thermal energy (heat) due to the resistance. The amount of heat produced can be determined by the formula:
\[P = I^2 R\]where:
  • \( P \): Power (heat) produced
  • \( I \): Current through the conductor
  • \( R \): Resistance of the conductor
In the problem at hand, we calculate the average power loss due to Joule heating in the coil by using the maximum current and resistance. Since the current varies sinusoidally in this setup, the average power can also be determined using:
\[P_{avg} = \frac{1}{2} \varepsilon_{max} I_{max}\]In this instance, with a resistance of 10 Ω and a maximum current of 0.06 A, the average power loss due to Joule heating is found to be 0.018 W. This formula shows how resistance can convert electrical energy into heat, emphasizing the importance of resistor efficiency in electronic devices.
Ohm's Law
Ohm's Law is a fundamental principle that describes the relationship between voltage, current, and resistance in an electrical circuit. It is expressed by the equation:
\[V = IR\]where:
  • \( V \): Voltage across the conductor
  • \( I \): Current flowing through the conductor
  • \( R \): Resistance of the conductor
In our context, Ohm's Law is instrumental in determining the maximum current (\( I_{max} \)) that flows through the coil when the maximum emf (\( \varepsilon_{max} \)) is induced. By rearranging the formula, we find that:
\[I_{max} = \frac{\varepsilon_{max}}{R}\]This calculation shows how voltage applied to a circuit and resistance within that circuit determines the current. For this exercise, with \( \varepsilon_{max} = 0.60 \, V \) and resistance \( R = 10 \, \Omega \), the resultant maximum current is 0.06 A. Understanding Ohm's Law helps in predicting how circuits will respond to changing electrical conditions.

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Most popular questions from this chapter

A circular coil of diameter \(21 \mathrm{~cm}\) is held in a magnetic field of induction \(10^{-4} \mathrm{~T}\). The magnitude of magnetic flux linked with the coil when the plane of the coil makes an angle of \(30^{\circ}\) with the field is (a) \(3.1 \times 10^{-6} \mathrm{~Wb}\) (b) \(1.414 \mathrm{~Wb}\) (c) \(1.73 \times 10^{-6} \mathrm{~Wb}\) (d) \(14.14 \mathrm{~Wb}\)

Two coils \(X\) and \(Y\) are placed in a circuit such that a current changes by \(2 \mathrm{~A}\) in coil \(X\) and magnetic flux change of \(0.4\) Wb occurs in \(Y\). The value of mutual inductance of the coils is (a) \(0.8 \mathrm{H}\) (b) \(0.2 \mathrm{~Wb}\) (c) \(0.2 \mathrm{H}\) (d) \(5 \mathrm{H}\)

Assertion In a series \(R-L-C\) circuit the voltage across resistor, inductor and capacitor are \(8 \mathrm{~V}, 16 \mathrm{~V}\) and \(10 \mathrm{~V}\) respectively. The resultant emf the circuit is \(10 \mathrm{~V}\). Reason Resultant emf of the circuit is given by the relation \(E=\sqrt{V_{R}^{2}+\left(V_{L}-V_{C}\right)^{2}}\)

An aeroplane in which the distance between the tips of the wings in \(50 \mathrm{~m}\) is flying horizontally with a speed of \(360 \mathrm{kmh}^{-1}\) over a place where the vertical component of earth's magnetic field is \(2 \times 10^{-4} \mathrm{Wbm}^{-2}\). The potential difference between the tips of the wings would be (a) \(0.1 \mathrm{~V}\) (b) \(1.0 \mathrm{~V}\) (c) \(0.2 \mathrm{~V}\) (d) \(0.01 \mathrm{~V}\)

If number of turns in primary and secondary coils is increased to two times each, the mutual inductance (a) becomes 4 times (b) becomes 2 times (c) becomes \(1 / 4\) times (d) remains unchanged

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