Question:

A straight wire of mass $200\, g$ and length $1.5\, m$ carries a current of $2\, A$. It is suspended in mid-air by a uniform horizontal magnetic field $B$. The magnitude of $B$ (in tesla) is (assume $g=9.8\, ms ^{-2}$ )

Updated On: Jul 5, 2022
  • 2
  • 1.5
  • 0.55
  • 0.65
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The Correct Option is D

Solution and Explanation

Magnetic force on straight wire $F=$ Bil $\sin \theta=$ Bil $\sin 90^{\circ}=$ Bil For equilibrium of wire in mid-air, $F =m g$ $Bil =m g$ $\therefore B=\frac{m g}{il}=\frac{200 \times 10^{-3} \times 9.8}{2 \times 1.5}$ $=0.65\, T$
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Top Questions on Magnetic Field Due To A Current Element, Biot-Savart Law

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Concepts Used:

Biot Savart Law

Biot-Savart’s law is an equation that gives the magnetic field produced due to a current-carrying segment. This segment is taken as a vector quantity known as the current element. In other words, Biot-Savart Law states that if a current carrying conductor of length dl produces a magnetic field dB, the force on another similar current-carrying conductor depends upon the size, orientation and length of the first current carrying element. 

The equation of Biot-Savart law is given by,

\(dB = \frac{\mu_0}{4\pi} \frac{Idl sin \theta}{r^2}\)

Application of Biot Savart law

  • Biot Savart law is used to evaluate magnetic response at the molecular or atomic level.
  • It is used to assess the velocity in aerodynamic theory induced by the vortex line.

Importance of Biot-Savart Law

  • Biot-Savart Law is exactly similar to Coulomb's law in electrostatics.
  • Biot-Savart Law is relevant for very small conductors to carry current,
  • For symmetrical current distribution, Biot-Savart Law is applicable.

For detailed derivation on Biot Savart Law, read more