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Chapter 27: Problem 17

The restoring couple in the moving coil galvanometer is because of : (a) magnetic field (b) material of the coil (c) twist produced in the suspension (d) current in the coil

Short Answer

Expert verified
The restoring couple in a moving coil galvanometer is due to the twist produced in the suspension (option c).

Step by step solution

01

Understand the Context of the Problem

The question is asking about the cause of the restoring torque (restoring couple) in a moving coil galvanometer, which is a device used to measure small electric currents. A coil within the galvanometer experiences torque when current passes through it, and a restoring force attempts to return it to equilibrium.
02

Analyze the Options

We have four options to consider: (a) magnetic field, (b) material of the coil, (c) twist produced in the suspension, and (d) current in the coil. We need to determine which one contributes to the restoring torque experienced by the coil within the galvanometer.
03

Evaluate Option (a) - Magnetic Field

A magnetic field interacts with the current-carrying coil to produce the initial deflection (causing it to move), but it does not directly produce the restoring torque that attempts to bring the coil back to its original position.
04

Evaluate Option (b) - Material of the Coil

The material of the coil determines its electrical properties, but it does not contribute to the restoring couple. It affects resistance and current flow but not the restoring force directly.
05

Evaluate Option (c) - Twist Produced in the Suspension

This option refers to the tension or torsion in the wire or suspension supporting the coil. As the coil deflects, the suspension wire twists, generating a restoring torque due to its elasticity and resistance to twisting.
06

Evaluate Option (d) - Current in the Coil

While the current in the coil is necessary for the initial movement, by interacting with the magnetic field, it does not create the restoring torque itself. It causes deflection in the presence of a magnetic field.
07

Conclusion

The restoring torque in a moving coil galvanometer is primarily due to the twist produced in the suspension wire (option c), which acts like a spring to bring the coil back to its equilibrium position.

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Key Concepts

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

Restoring Torque
In a moving coil galvanometer, restoring torque plays a vital role in returning the coil to its equilibrium position after deflection. When electric current flows through the coil, it moves under the influence of a magnetic field. However, a restoring force is necessary to bring the coil back to its original orientation once the current stops. This restoring torque arises as the coil deflects, causing the suspension wire to twist. It is similar to the action of a spring, where the wire's torsional resistance generates a force to restore the initial position. This torque ensures that the galvanometer can accurately measure changes in current as it provides the necessary counterbalance to the coil's movement.
Suspension Wire Twist
The suspension wire in a galvanometer is more than just a support structure; it is crucial for generating the restoring force due to its twist. As the coil inside the galvanometer deflects due to current flow, the suspension wire begins to twist. This twisting is not arbitrary. It is the wire's natural resistance to being twisted that creates the restoring torque to move the coil back towards its start position. - The thickness and material of the suspension wire influence how easily it twists. - A thinner wire would offer less resistance, resulting in a less firm restoring force. - Conversely, a thicker wire increases the resistance and potentially the accuracy of measurement. By functioning like a torsional spring, the suspension wire ensures that the galvanometer can return to neutral reliably and consistently, ensuring precise measurements.
Electric Current Measurement
Measuring electric current with a moving coil galvanometer involves a delicate interplay of forces. The galvanometer is designed to detect small amounts of current by using the interaction between the magnetic field and the current-carrying coil. Here's how it works: - An electric current enters the coil, creating its own magnetic field. - This magnetic field interacts with a fixed external field, producing a torque that deflects the coil. - The angular deflection is proportional to the current intensity, enabling the calibration of the scale for current measurement. As the coil deflects, the twist in the suspension wire generates a restoring torque that brings the coil back to equilibrium when the current is turned off. Thus, understanding this interaction helps in accurately measuring and interpreting electric current values using a galvanometer.

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Most popular questions from this chapter

A positive charge is released from the origin at a place where uniform electric field \(E\) and a uniform magnetic field \(B\) exist along the positive \(y\) -axis and positive \(z\) -axis respectively, then: (a) initially the charge particle tends to move along positive \(z\) -axis (b) initially the charged particle tends to move along negative \(y\) -direction (c) initially the charged particle tends to move along positive \(y\) -direction (d) the charged particle moves in \(y-z\) plane

Mark correct option or options: (a) Electric field and magnetic field are basically independent (b) Electric field and magnetic field are two aspects of the electromagnetic field (c) Electric field and magnetic field may be produced by charge in rest (d) Both (a) and (c) are correct

A charged particle enters into a uniform magnetic field \(B\) with velocity \(\vec{v}\) at an angle \(\theta\) as shown in figure. Then the ratio of radius to pitch of helix is: (a) \(\frac{2 \pi}{\tan \theta}\) (b) \(\tan \theta\) (c) \(\cot \theta\) (d) \(\frac{\tan \theta}{2 \pi}\)

A charged particle of mass \(m\) and charge \(q\) is accelerated through a potential difference of \(V\) volt. It enters a region of uniform magnetic field which is directed perpendicular to the direction of motion of the particie. The particle will move on a circular path of radius given by: (a) \(\sqrt{\left(\frac{V m}{q B^{2}}\right)}\) (b) \(\frac{2 V m}{q B^{2}}\) (c) \(\sqrt{\left(\frac{2 V_{m}}{q}\right)}\left(\frac{1}{B}\right)\) (d) \(\sqrt{\left(\frac{V m}{q}\right)}\left(\frac{1}{B}\right)\)

The ratio of the energy required to set-up in a cube of side \(10 \mathrm{~cm}\) in a uniform magnetic field of \(4 \mathrm{~Wb} / \mathrm{m}^{2}\) and a uniform electric field of of \(10^{6} \mathrm{~V} / \mathrm{m}\), is: (a) \(1.44 \times 10^{7}\) (b) \(1.44 \times 10^{-5}\) (c) \(1.44 \times 10^{6}\) (d) \(1.44 \times 10^{3}\)
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