Advertisements
Advertisements
Question
A very long bar magnet is placed with its north pole coinciding with the centre of a circular loop carrying as electric current i. The magnetic field due to the magnet at a point on the periphery of the wire is B. The radius of the loop is a. The force on the wire is
Options
very nearly 2πaiB perpendicular to the plane of the wire
2πaiB in the plane of the wire
πaiB along the magnet
zero
Advertisements
Solution
very nearly `2pi aiB` perpendicular to the plane of the wire
In this case, the north pole of the magnet is coinciding with the centre of the circular loop carrying electric current i. So, the magnetic field lines almost lie on the plane of the ring and the force due to the field lines is perpendicular to the field lines and to the plane of the circular ring.
Let idl be the current element, B be the magnetic field and dF be the force on the current element idl.
Now
`dF = B i dl ⇒ F = ∫_0^(2pia) B i dl`
⇒ `F = 2pi a iB`
Thus, the force acting on the wire is `2pi a iB` and it is perpendicular to the plane of the wire.
APPEARS IN
RELATED QUESTIONS
State two advantages of an electromagnet over a permanent magnet.
Write two characteristics of a material used for making permanent magnets ?
A dip circle is taken to geomagnetic equator. The needle is allowed to move in a vertical plane perpendicular to the magnetic meridian. The needle will stay ______.
Which of the following four graphs may best represent the current-deflection relation in a tangent galvanometer?
Two long bare magnets are placed with their axes coinciding in such a way that the north pole of the first magnet is 2.0 cm from the south pole of the second. If both the magnets have a pole strength of 10 Am, find the force exerted by one magnet of the other.
The magnetic field at a point, 10 cm away from a magnetic dipole, is found to be `2.0 xx 10^-4 "T"` . Find the magnetic moment of the dipole if the point is (a) in end-on position of the dipole and (b) in broadside-on position of the dipole.
Do permeability and relative permeability have the same dimensions?
Why is it not possible to make permanent magnets from paramagnetic materials?
The magnetic moment of the assumed dipole at the earth's centre is 8.0 × 1022 A m2. Calculate the magnetic field B at the geomagnetic poles of the earth. Radius of the earth is 6400 km.
A magnetic needle is free to rotate in a vertical plane which makes an angle of 60° with the magnetic meridian. If the needle stays in a direction making an angle of `tan^-1(2sqrt(3))` with the horizontal, what would be the dip at that place?
The needle of a dip circle shows an apparent dip of 45° in a particular position and 53° when the circle is rotated through 90°. Find the true dip.
The magnetometer of the previous problem is used with the same magnet in Tan-B position. Where should the magnet be placed to produce a 37° deflection of the needle?
A bar magnet takes π/10 second the complete one oscillation in an oscillation magnetometer. The moment of inertia of the magnet about the axis of rotation is 1.2 × 10−4 kg m2 and the earth's horizontal magnetic field is 30 μT. Find the magnetic moment of the magnet.
Which property of soft iron makes it useful for preparing electromagnet?
In a permanent magnet at room temperature ______.
A steel wire of length 1 has a magnetic moment m it is then bent into a semicircular arc. The new magnetic moment is
Which of the following is most suitable for the core of an electromagnet?
