What is the magnetic field at point O in the figure?
                    

1.  $\frac{{\mu }_{0}I}{4\mathrm{\pi r}}$                                  
2.  $\frac{{\mu }_{0}I}{4\mathrm{\pi r}}+\frac{{\mu }_{0}I}{2\mathrm{\pi r}}$
3.  $\frac{{\mu }_{0}I}{4r}+\frac{{\mu }_{0}I}{4\mathrm{\pi r}}$                        
4.  $\frac{{\mu }_{0}I}{4r}-\frac{{\mu }_{0}I}{4\mathrm{\pi r}}$

If the current is flowing in the south direction along a power line, then what will be the direction of the magnetic field above the power line (neglecting the earth's field)?

If a wire in the form of a square with a side ‘a’ carries a current i, then the magnetic induction at the centre of the square wire will be:
(Magnetic permeability of free space = ${\mathrm{\mu }}_0$)

A proton and an α- particle enter a uniform magnetic field perpendicularly at the same speed. If a proton takes 25 μs to make 5 revolutions, then the periodic time for the α-particle will be:

1. 50 $\mathrm{\mu }$s               

2. 25 $\mathrm{\mu }$s 

3. 10 $\mathrm{\mu }$s                 

4. 5 $\mathrm{\mu }$s

Which among the following options needs to be decreased to increase the sensitivity of a moving coil galvanometer?

In a hydrogen atom, the electron makes 6.6×10¹⁵ rev/sec around the nucleus in an orbit of radius 0.528 Å. What will (A-m²) its magnetic moment be?
1. $1\times {10}^{-15}$                     

2. $1\times {10}^{-10}$

3. $1\times {10}^{-23}$                      

4. $1\times {10}^{-27}$

What is a representation of the magnetic field caused by a straight conductor with a uniform cross-section and a steady current of radius 'a'?

1.		2.
3.		4.

A particle of charge q and mass m is moving along the x-axis with a velocity of v and enters a region of electric field E and magnetic field B as shown in the figure below. For which figure is the net force on the charge zero?

1.		2.
3.		4.

A current-carrying wire is placed in a uniform magnetic field in the shape of the curve \(y= \alpha sin ({\pi x \over L}),~0 \underline{<}x \underline{<}~2L\) $$
. What will be the force acting on the wire?
                   

A circular coil is in the y-z plane with its centre at the origin. The coil carries a constant current. Assuming the direction of the magnetic field at x = – 25 cm to be positive, which of the following graphs shows the variation of the magnetic field along the x-axis?

1.		2.
3.		4.