Magnetic poles and magnetic compass - class-VII
magnetic poles and magnetic compass
Questions
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
- ${0}^{o}$
- ${90}^{o}$
- ${45}^{o}$
- ${180}^{o}$
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
- $cos^{-1} \left (\cfrac 1{\sqrt 3}\right)$
- $cos^{-1} \left (\cfrac {\sqrt 3}{2}\right)$
- $cos^{-1} \left (\cfrac {1}{2}\right)$
- $cos^{-1} \left (\cfrac { 1}{\sqrt2}\right)$
If earth's magnetic field $B _H$, if the frequency of oscillation of a magnetic needle is n, then -
- $ n \propto B _H$
- $ n^2 \propto B _H$
- $ n \propto B _H^2$
- $n^2 \propto \frac{1}{B _H}$
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
- $4.5 \ A m^2$
- $0.45 \ A m^2$
- $0.75 \ A m^2$
- $0.225 \ A m^2$
A magnetic needle is kept in a nonuniform magnetic field. It
- may experience a force but certainly not a torque
- may experience a torque but certainly not a force
- may experience both a torque as well as force
- will certainly experience neither a force not a torque
The needle of a dip circle when place at a geomagnetic pole stays along
- south-north direction only
- east-west direction only
- vertical direction
- horizontal direction
Which of the following helps detecting the presence of magnetic field at a point ?
- a strong magnet
- a solenoid
- a compass needle
- a current carrying wire
What kind of magnet is used in a magnetic compass ?
- electromagnet
- permanent magnet
- temporary magnet
- none of the above
What is the circular enclosure that the magnetic compass is placed in ?
- iron case
- stainless steel case
- aluminium case
- nickel case
A device used by the sailors to find the direction in which their ship is moving is called .................
- horse shoe
- curve
- magnetic field
- magnetic needle
State whether true or false:
- True
- False
The presence of magnetic field at a point can be detected by
- ammeter
- galvanometer
- a compass needle
- strong magnet
The magnetic compass is not useful for navigation near the magnetic poles, since
- $R=0$
- $V=0$
- $H=0$
- $\theta={0}^{o}$
A magnetic needle oscillates in a horizontal plane with a period $T$ at a place where the angle of dip is $60^0$. When the same needle is made to oscillate in a vertical plane coinciding with the magnetic meridian, its period will be
- $\frac{T}{\sqrt 2}$
- T
- 2T
- 6T
When a current of $1$ ampere is passed in a coil lying in the magnetic meridian then a magnetic needle at its centre gives some deflection. If the current in the coil is increased to $\sqrt8$ ampere then at what distance from the centre of the coil will the deflection of needle remains underchanged?
- $2R$
- $4R$
- $8R$
- $R$