Tag: magnetic poles and magnetic compass

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Questions Related to magnetic poles and magnetic compass

Multiple choice magnetic compass magnetic poles and magnetic compass properties of magnet effect of electric current physics

Bar magnets always align themselves in the North-South direction when suspended freely in air.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A freely suspended magnet always points in the north south direction as earth behaves as large magnet. the north pole of the earth's magnet attracts the south pole of the magnet and vice versa.

Note: The north pole of earth's magnet is in geographical south because it attracts the south pole of the suspended magnet.

Multiple choice magnetic compass magnetic poles and magnetic compass properties of magnet effect of electric current physics

A small plotting compass can be used to plot a magnetic field because 

  1. the compass needle is freely suspended magnet

  2. the compass needle is easily demagnetized

  3. there is a vacuum inside the case of the compass

  4. the Earth's magnetic field has no effect on the needle
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The compass needle acts as a freely suspended magnet which points in north-south direction under the influence of earth's magnetic field lines. So, a small plotting compass can be used to plot a magnetic field.

Multiple choice magnetic compass magnetic poles and magnetic compass properties of magnet effect of electric current physics

A magnetic compass shows a deflection when placed near a current carrying wire. If the current in the wire is increased, How does the deflection of the compass gets affected ?

  1. increased

  2. decreased

  3. remain same

  4. data insufficient
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When a magnetic compass is brought close to a current carrying wire there is deflection in the compass due to the formation of magnetic field. The magnetic field lines around a long wire which carries an electric current form concentric circles around the wire. The direction of the magnetic field is perpendicular to the wire. 
The deflection increases when the current is increased because the magnitude of the field is directly proportional to the strength of the electric current. That is, stronger the electric field, stronger the magnetic field.

Multiple choice magnetic compass magnetic poles and magnetic compass properties of magnet effect of electric current physics

For a vibration magnetometer, the time period of a freely suspended bar magnet can be reduced by:

  1. Moving it towards south pole

  2. Moving it towards north pole

  3. Moving it towards equator

  4. None
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

we know,
The time period of vibration magnetometer is,
$T = 2\pi \sqrt {\dfrac{1}{{mH}}} $
For some moment of inertia $I$ and magnetic moment $m$
$T \propto \dfrac{1}{{\sqrt H }}$
T can be reduced if horizontal component of earth's magnetic field $H$ is increased. But
$H = R\cos \theta $
$H$ is high if the dip is zero.
This occurs at the equator.
Hence the period can be reduced by moving towards the equator.

Multiple choice magnetic compass magnetic poles and magnetic compass properties of magnet effect of electric current physics

At a certain location in Africa, compass points $12^0$ west of geographic north. The north tip of magnetic needle of a dip circle placed in the plane of magnetic meridian points $60^0$ above the horizontal. The horizontal component of earth's field is measured to be $0.16$G. The magnitude of earth's field at the location is :

  1. $0.32$G

  2. $0.42$G

  3. $4.2$G

  4. $3.2$G
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Here, $H _E = 0.16G = 0.16 \times 10^{-4}T$, dip angle $(\delta) = 60^0$
Then, magnitude of earth's field.
$B _E = \dfrac{H _E}{cos \delta} = \dfrac{0.16 \times 10^{-4}}{cos 60^0} T \Rightarrow B _E = \dfrac{0.16 \times 10^{-4}}{1/2} = 0.32 \times 10^{-4}T = 0.32G$

Multiple choice magnetic compass magnetic poles and magnetic compass properties of magnet effect of electric current physics

On the basis of following features identify the correct option 
I. They always start from north pole and end at the south pole of the magnet outside the magnet.
II. They never intersect each other.

  1. Electric lines of force

  2. Magnetic lines of force

  3. Both (1) and (2)

  4. Neither (1) nor (2)
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Properties of magnetic lines of force
(i) they always start from north pole and end at the south pole of the magnet outside the magnet.
(ii) they never intersect each other.