Magnetic Force

A cubical region of space is filled with some uniform electric and magnetic fields. An electron enters the cube across one of its faces with velocity v and a positron enters via opposite face with velocity – v. At this instant ______.

1. the electric forces on both the particles cause identical accelerations.
2. the magnetic forces on both the particles cause equal accelerations.
3. both particles gain or loose energy at the same rate.
4. the motion of the centre of mass (CM) is determined by B alone.

Show that a force that does no work must be a velocity dependent force.

Figure shows a square loop. 20 cm on each side in the x-y plane with its centre at the origin. The loop carries a current of 7 A. Above it at y = 0, z = 12 cm is an infinitely long wire parallel to the x axis carrying a current of 10 A. The net force on the loop is ______ × 10^-4 N.

For a circular coil of radius R and N turns carrying current I, the magnitude of the magnetic field at a point on its axis at a distance x from its centre is given by,

B = `(μ_0"IR"^2"N")/(2("x"^2 + "R"^2)^(3/2))`

(a) Show that this reduces to the familiar result for field at the centre of the coil.

(b) Consider two parallel co-axial circular coils of equal radius R, and number of turns N, carrying equal currents in the same direction, and separated by a distance R. Show that the field on the axis around the mid-point between the coils is uniform over a distance that is small as compared to R, and is given by, B = `0.72 (μ_0"NI")/"R"` approximately.

[Such an arrangement to produce a nearly uniform magnetic field over a small region is known as Helmholtz coils.]

The magnetic moment is NOT associated with ____________.

An infinitely long straight conductor carries a current of 5 A as shown. An electron is moving with a speed of 10⁵ m/s parallel to the conductor. The perpendicular distance between the electron and the conductor is 20 cm at an instant. Calculate the magnitude of the force experienced by the electron at that instant.

A magnetic field exerts no force on

Direction of magnetic force on a positive charge moving in a magnetic field is given by ______.