Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Magnetics question

2019 · 9 Apr · Shift 2 · Q67
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Physics
  4. /Magnetics
  5. /2019 · 9 Apr · Shift 2 · Q67

Magnetics question

2019 · 9 Apr · Shift 2 · Q67

JEE MainPhysicsMagneticsMCQ+4 / −1
A moving coil galvanometer has a coil with 175 turns and area 1 cm2. It uses a torsion band of torsion constant 10–6 N-m/rad. The coil is placed in a maganetic field B parallel to its plane. The coil deflects by 1° for a current of 1 mA. The value of B (in Tesla) is approximately :-
  1. A
    10–4
  2. B
    10–2
  3. C
    10–1
  4. D
    10–3
View written solutionFree

Correct answer: D

  1. Torque balance in a moving coil galvanometer

When current III flows in the coil, magnetic torque is balanced by restoring torque:

NABI=CθNABI = C\thetaNABI=Cθ

where:

  • N=175N = 175N=175
  • A=1 cm2=10−4 m2A = 1\text{ cm}^2 = 10^{-4}\text{ m}^2A=1 cm2=10−4 m2
  • C=10−6 N m/radC = 10^{-6}\text{ N m/rad}C=10−6 N m/rad
  • θ=1∘=π180 rad\theta = 1^\circ = \frac{\pi}{180}\text{ rad}θ=1∘=180π​ rad
  • I=1 mA=10−3 AI = 1\text{ mA} = 10^{-3}\text{ A}I=1 mA=10−3 A

Since the magnetic field is parallel to the plane of the coil, the angle between the normal to the coil and B⃗\vec BB is 90∘90^\circ90∘, so magnetic torque is maximum:

τ=NABI\tau = NABIτ=NABI

  1. Substitute values

B=CθNAIB = \frac{C\theta}{NAI}B=NAICθ​

So,

B=10−6⋅π180175⋅10−4⋅10−3B = \frac{10^{-6} \cdot \frac{\pi}{180}}{175 \cdot 10^{-4} \cdot 10^{-3}}B=175⋅10−4⋅10−310−6⋅180π​​

  1. Simplify

Denominator:

175⋅10−7=1.75×10−5175 \cdot 10^{-7} = 1.75 \times 10^{-5}175⋅10−7=1.75×10−5

Numerator:

10−6⋅π180≈10−6⋅0.01745=1.745×10−810^{-6} \cdot \frac{\pi}{180} \approx 10^{-6} \cdot 0.01745 = 1.745 \times 10^{-8}10−6⋅180π​≈10−6⋅0.01745=1.745×10−8

Thus,

B=1.745×10−81.75×10−5≈0.997×10−3≈10−3 TB = \frac{1.745 \times 10^{-8}}{1.75 \times 10^{-5}} \approx 0.997 \times 10^{-3} \approx 10^{-3}\text{ T}B=1.75×10−51.745×10−8​≈0.997×10−3≈10−3 T

  1. Match with options

B≈10−3 TB \approx 10^{-3}\text{ T}B≈10−3 T

So the correct option is D.

PreviousNext

More from Magnetics

  • An infinitely long current carrying wire and a small current carrying loop are in the plane of the paper as shown. The radius of the loop is a and distance of its centre from the wire is d (d > > a). If the loop a applies a force F… Includes diagram2019 · MCQ
  • A current loop, having two circular arcs joined by two radial lines is shown in the figure. It carries a current of 10 A. The magnetic field at point O will be close to : Includes diagram2019 · MCQ
  • One of the two identical conducting wires of length L is bent in the form of a circular loop and the other one into a circular coil of N identical turns. If the same current is passed in both, the radio of the magnetic field at the central…2019 · MCQ
  • A particle having the same charge as of electron moves in a ciurcular path of radius 0.5 cm under the influence of a magnetic field 0f 0.5 T. If an electric field of 100 V/m makes it to move in a straight path, then the mass of the…2019 · MCQ
  • A proton, an electron, and a Helium nucleus, have the same energy. They are in circular orbits in a plane due to magnetic field perpendicualr to the plane. Let rp, re and rHe be their respective radii, then2019 · MCQ
  • Two wires A & B are carrying currents I1 & I2 as shown in the figure. The separation between them is d. A third wire C carrying a current I is to be kept parallel to them at a distance x from A such that the net force acting on it… Includes diagram2019 · MCQ
  • The magnitude of the magnetic field at the centre of an equilateral triangular loop of side 1 m which is carrying a current of 10 A is : [Take μ 0 = 4 π × 10–7 NA–2]2019 · MCQ
  • A square loop is carrying a steady current I and the magnitude of its magnetic dipole moment is m. if this square loop is changed to a circular loop and it carries the same current, the magnitude of the magnetic dipole moment of circular…2019 · MCQ