Question:

A dip needle vibrates in a vertical plane perpendicular to magnetic meridian. The time of vibration is found to be $2 \,s$, the same needle is then allowed to vibrate in the horizontal plane and the time period is again found to be $2 \,s$. Then, the angle of dip is

Updated On: Jun 23, 2023
  • $0^{\circ}$
  • $30^{\circ}$
  • $45^{\circ}$
  • $90^{\circ}$
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The Correct Option is C

Solution and Explanation

Time of vibration is $T=2\pi\sqrt{\frac{I}{MB}}$ In first case $T_{1}=2\pi\sqrt{\frac{I}{MB_{V}}}$ In second case $T_{2}=2\pi\sqrt{\frac{I}{MB_{H}}}$ Divide $\left(ii\right)$ by $\left(i\right)$, we get $\therefore \frac{T_{2}}{T_{1}}=\sqrt{\frac{B_{V}}{B_{H}}}$ As $tan\,\delta=\frac{B_{V}}{B_{H}}$ where $\delta$ is the angle of dip $\therefore \frac{T_{2}}{T_{1}}=\sqrt{tan\,\delta}$ As $T_{2}=T_{1}=2\,s$ $\therefore tan\delta=1$ $\delta=tan^{-1}\left(1\right)=45^{\circ}$
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Concepts Used:

Magnetism & Matter

Magnets are used in many devices like electric bells, telephones, radio, loudspeakers, motors, fans, screwdrivers, lifting heavy iron loads, super-fast trains, especially in foreign countries, refrigerators, etc.

Magnetite is the world’s first magnet. This is also called a natural magnet.  Though magnets occur naturally, we can also impart magnetic properties to a substance. It would be an artificial magnet in that case.

Read More: Magnetism and Matter

Some of the properties of the magnetic field lines are:

  • The lines and continuous and outside the magnet, the field lines originate from the North pole and terminate at the South pole
  • They form closed loops traversing inside the magnet. 
  • But here the lines seem to originate from the South pole and terminate at the North pole to form closed loops.
  • More number of close lines indicate a stronger magnetic field
  • The lines do not intersect each other
  • The tangent drawn at the field line gives the direction of the field at that point.