Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE Main 20198 AprilMorning Shift
Exam
JEE Main
Year
2019
Date
8 April
Shift
Morning Shift
Subject
Physics
Chapter
Electromagnetic Induction

JEE Main 2019 · 8 April · Morning Shift · Physics · Electromagnetic Induction

A thin strip 10cm long is on a U shaped wire of negligible...

A thin strip 10cm10cm long is on a UU shaped wire of negligible resistance and it is connected to a spring of spring constant 0.5Nm−10.5N{m}^{- 1} (see figure). The assembly is kept in a uniform magnetic field of 0.1T.0.1T . If the strip is pulled from its equilibrium position and released, the number of oscillations it performs before its amplitude decreases by a factor of ee is NN . If the mass of the strip is 5050 grams, its resistance 10Ω10Ω and air drag negligible, NN will be close to:
A thin strip 10cm long is on a U shaped wire of negligible resistance and it is connected to a spring of spring

Options

  1. A10001000
  2. B50005000
  3. C1000010000
  4. D5000050000

Correct answer

B. 50005000

Step-by-step solution

Equation of motion for slider:
−md2xdt2=kx+ilB- m\dfrac{{d}^{2}x}{d{t}^{2}} = kx + ilB
md2xdt2+kx+(BlvR)lB=0⇒md2xdt2+B2l2R.dxdt+kx=0m\dfrac{{d}^{2}x}{d{t}^{2}} + kx + \left(\dfrac{Blv}{R}\right)lB = 0 ⇒ m\dfrac{{d}^{2}x}{d{t}^{2}} + \dfrac{{B}^{2}{l}^{2}}{R} . \dfrac{dx}{dt} + kx = 0
Comparing with md2xdt2+b.dxdt+kx=0m\dfrac{{d}^{2}x}{d{t}^{2}} + b . \dfrac{dx}{dt} + kx = 0
m=m;b=B2l2R;k=km = m; b = \dfrac{{B}^{2}{l}^{2}}{R}; k = k
We know: A=A0e−b2m×t=A0e−B2l22mR×tA = {A}_{0}{e}^{\dfrac{- b}{2m} \times t} = {A}_{0}{e}^{- \dfrac{{B}^{2}{l}^{2}}{2mR} \times t}
For amplitude to be A0/e,{A}_{0} / e,
A0e−B2l22mR×t=Ae⇒B2l22mR×t=1{A}_{0}{e}^{- \dfrac{{B}^{2}{l}^{2}}{2mR} \times t} = \dfrac{A}{e} ⇒ \dfrac{{B}^{2}{l}^{2}}{2mR} \times t = 1
t=2mRB2l2=10,000sect = \dfrac{2mR}{{B}^{2}{l}^{2}} = 10,000sec
Time period = 2πmk=2s2\pi\sqrt{\dfrac{m}{k}} = 2s
Number of oscillations = 10,0002=5,000\dfrac{10,000}{2} = 5,000
Practice Electromagnetic Induction on Quantrex Academy →

More from Electromagnetic Induction

List-I contains four conducting loops lying in the XY plane, as shown in the figures. The… JEE Advanced 2026A 30 cm long solenoid has 10 turns per cm and area of 5 cm ^2 . The current through the… JEE Main 2026A square loop of side 2 cm is placed in a time varying magnetic field with magnitude as B… JEE Main 2026An inductor of inductance 10 mH having resistance of 100\,Ω is connected to battery of… JEE Main 2026A metal rod of length L rotates about one end at origin with a uniform angular velocity ω… JEE Main 2026A circular loop of radius 20 cm and resistance 2\ Ω is placed in a time varying magnetic… JEE Main 2026In the given circuit below inductance values of L_1 , L_2 and L_3 are same. The magnetic… JEE Main 2026A circular current loop of radius R is placed inside square loop of side length L (L >>… JEE Main 2026 Full Electromagnetic Induction list All JEE Main PYQs