A coil having N turns carry a current as shown in the figure. The magnetic field intensity at point  P 

• $\frac{{\mathrm{\mu }}_0{\mathrm{NiR}}^2}{2{\left({\mathrm{R}}^2+{\mathrm{x}}^2\right)}^{{\displaystyle \raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}}$

• $\frac{{\mathrm{\mu }}_0\mathrm{Ni}}{2\mathrm{R}}$

• $\frac{{\mathrm{\mu }}_0 {\mathrm{NiR}}^2}{{\left(\mathrm{R}+\mathrm{x}\right)}^2}$

• Zero

An electron moves at right angle to a magnetic field of 1.5×10^-2 T with a speed of 6 x 10⁷ m / s. If the specific charge of the electron is 1.7x 10¹¹ C/ kg. The radius of the circular path will be

• 2.9 cm

• 3.9 cm

• 2.35 cm

• 2 cm

If a charge particle enters perpendicularly in the uniform magnetic field, then:

• energy and momentum both remains constant

• energy remains constant but momentum changes

• both energy and momentum changes

• energy changes but momentum remains constant 

204.

A coil in the shape of an equilateral triangle of side l is suspended between the pole pieces of a permanent magnet such that B is in plane of the coil. If due to current i in the triangle a torque T acts on it, the side l of the triangle is

• 

• 

• 

• 

An electron moves in a circular orbit with a uniform speed v. It produces a magnetic field B at the centre of the circle. The radius of the circle is proportional, to

• B/v

• v/B

• √v/B

• √B/v

In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular paths of radius R using a magnetic field B. If V and B are kept constant the ratio $\left(\frac{\mathrm{charge} \mathrm{on} \mathrm{the} \mathrm{ion}}{\mathrm{mass} \mathrm{of} \mathrm{the} \mathrm{ion}}\right)$ will be proportional to

• $\frac{1}{\mathrm{R}}$

• $\frac{1}{{\mathrm{R}}^2}$

• R²

• R

The north pole of a long horizontal bar magnet is being brought closer to a vertical conducting plane along the perpendicular direction. The direction of the induced current in the conducting plane will be

• horizontal

• vertical

• clockwise

• Anticlockwise

An electric current passes through a long straight copper wire. At a distance 5 cm from the straight wire, the magnetic field is B. The magnetic field at 20 cm from the straight wire would be

• $\frac{\mathrm{B}}{6}$

• $\frac{\mathrm{B}}{4}$

• $\frac{\mathrm{B}}{3}$

• $\frac{\mathrm{B}}{2}$

An electron of mass m and charge q is travelling with a speed v along a circular path of radius r at right angles to a uniform magnetic field B. If speed of the electron is doubled and the magnetic field is halved, then resulting path would have a radius of

• $\frac{\mathrm{r}}{4}$

• $\frac{\mathrm{r}}{2}$

• 2r

• 4r

A galvanometer acting as a voltmeter should have

• low resistance in series with its coil

• low resistance in parallel with its coil

• high resistance in series with its coil

• high resistance in parallel with its coil