Tag: magnetic field

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Questions Related to magnetic field

Multiple choice properties of magnet magnetism physics neutral points magnetic poles and magnetic compass magnetic field

A DMM is arragned at the magnetic pole of earth in $\tan{A}$ position. If a bar magnet is placed at some distance from the needle, deflection is

  1. ${0}^{o}$

  2. ${90}^{o}$

  3. ${45}^{o}$

  4. ${180}^{o}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

At the magnetic poles, the horizontal component of the Earth's magnetic field (BH) is zero. In a tan A position, the needle aligns with the resultant field. Since BH = 0, the needle will be vertical (dip = 90 degrees), but the question asks for deflection in a horizontal DMM setup, which results in 0 degrees as there is no horizontal field to deflect it.

Multiple choice properties of magnet magnetism physics neutral points magnetic poles and magnetic compass magnetic field

The needle of a dip circle shows an apparent dip of $45^o$ at a place and $60^o$ when the circle is rotated through $90^o$. The true dip is

  1. $cos^{-1} \left (\cfrac 1{\sqrt 3}\right)$

  2. $cos^{-1} \left (\cfrac {\sqrt 3}{2}\right)$

  3. <span>$cos^{-1} \left (\cfrac {1}{2}\right)$</span>

  4. <span>$cos^{-1} \left (\cfrac { 1}{\sqrt2}\right)$</span>
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice properties of magnet magnetism physics neutral points magnetic poles and magnetic compass magnetic field

If earth's magnetic field $B _H$, if the frequency of oscillation of a magnetic needle is n, then -

  1. $ n \propto B _H$

  2. $ n^2 \propto B _H$

  3. $ n \propto B _H^2$

  4. $n^2 \propto \frac{1}{B _H}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The time period of a magnetic needle oscillating in a magnetic field is T = 2 * pi * sqrt(I / (M * BH)). Since frequency n = 1/T, we have n = (1 / (2 * pi)) * sqrt(M * BH / I). Squaring both sides gives n^2 proportional to BH.

Multiple choice properties of magnet magnetism physics neutral points magnetic poles and magnetic compass magnetic field

An aeroplane, in which the distance between the tips of the wings is $50 m$, is flying horizontally with a speed of $360$ km/hour, over a place where the vertical component of earth's magnetic field is $2.0 \times 10^{-4} \ tesla$ . The potential difference between the tips of the wings would be

  1. $0.1 V$

  2. $0.5 V$

  3. $0.2 V$

  4. $1.0 V$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The induced EMF across the wings is e = B * v * l. Speed v = 360 km/h = 100 m/s. B = 2.0 * 10^-4 T. l = 50 m. e = (2.0 * 10^-4) * 100 * 50 = 1.0 V.

Multiple choice properties of magnet magnetism physics neutral points magnetic poles and magnetic compass magnetic field

In an uniform field the magnetic needle completes 10 oscillations in 92seconds. When a small magnet is placed in the magnetic meridian 10cm due north of needle with north pole towards south completes 15 oscillations in 69seconds. The magnetic moment of magnet ($B _H =0.3 \ G$) is

  1. $4.5 \ A m^2$

  2. $0.45 \ A m^2$

  3. $0.75 \ A m^2$

  4. $0.225 \ A m^2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Using the oscillation magnetometer formula, the ratio of frequencies squared is proportional to the ratio of fields. T1 = 9.2s, T2 = 4.6s. (n2/n1)^2 = (T1/T2)^2 = (9.2/4.6)^2 = 4. The field B_net = BH + B_magnet. Solving for M using the tan A position formula yields 4.5 Am^2.

Multiple choice properties of magnet magnetism physics neutral points magnetic poles and magnetic compass magnetic field

A magnetic needle is kept in a nonuniform magnetic field. It

  1. may experience a force but certainly not a torque

  2. may experience a torque but certainly not a force

  3. may experience both a torque as well as force

  4. will certainly experience neither a force not a torque
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

If magnet is placed parallel to the magnetic field then two poles of magnetic will experience different forces because of non uniform magnetic field. The forces will be in opposite direction therefore, there will be a net force also because forces are not equal. 
Now , when magnetic is not parallel to the magnetic field it will experience torque its a dipole placed in a field. Hence, (C)

Multiple choice properties of magnet magnetism physics neutral points magnetic poles and magnetic compass magnetic field

The needle of a dip circle when place at a geomagnetic pole stays along

  1. south-north direction only

  2. east-west direction only

  3. vertical direction

  4. horizontal direction
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Dip is the angle between the Earth's magnetic field and horizontal plane at that point. The needle of a dip circle when place at a geomagnetic poles stays along vertical direction.