A infinite straight wire carrying current 3 A and other carrying 6 A in the same direction produce a magnetic field of 12 tesla at the midpoint of the line joining them. When 6-ampere current wire is switched off, the magnetic field will be :

                                        

1. 24 T

2. 3 T

3. 6 T

4. 12 T

The magnetic field at origin in the situation shown in the figure has magnitude (BCD is a semi-circular arc of radius R in xz plane) 

1. $\frac{{\mu }_{0}l}{4\mathrm{\pi R}}$

2. $\frac{{\mu }_{0}l}{2\mathrm{\pi R}}\sqrt{4+{\mathrm{\pi }}^2}$

3. $\frac{{\mu }_{0}l}{2\mathrm{\pi R}}\sqrt{R^2+{\mathrm{\pi }}^2}$

4. $\frac{{\mu }_{0}l}{4\mathrm{\pi R}}\sqrt{1+{\mathrm{\pi }}^2}$

Three long straight wires A, B, and C are shown in figure. The resultant magnetic force on wire B is 

1. Towards left

2. Towards right

3. Upwards (perpendicular to the plane of paper)

4. Downwards (perpendicular to the plane of paper)

In a moving coil galvanometer the deflection $\theta$ of the coil is related to the electric current by the relation

1. $l\propto \tan \theta$

2. $l\propto \cos \theta$

3. $l\propto \theta$

4. $l\propto {\theta }^2$

A half-metre long wire is lying in a plane perpendicular to the magnetic field. A force of 2 kg wt is acting on it in a magnetic field of 0.98 tesla. The current flowing in it will be

1. 400 A 

2. 40 A

3. 4 A

4. 1 A

A cyclotron cannot be used to accelerate 

1. Deutrons 

2. Protons 

3. Neutrons

4. Both (1) & (3)

As indicated, a long, straight conductor XY carrying a current i₁ is placed antiparallel to a conductor AB of length l carrying a current i₂. How much of a force is acting on AB?

1. ${\mu }_0{i}_1{i}_2$

2.  $\frac{{\mu }_0{i}_1{i}_2}{\mathrm{\pi }}$

3. $\frac{{\mu }_0{i}_1{i}_2}{2\mathrm{\pi }}$

4. $2{\mu }_0{i}_1{i}_2$

Two long straight conductors with currents $l_1 and l_2$ are placed along X and Y-axes. The locus of points of zero magnetic induction is

1. A parabola

2. A rectangular hyperbola

3. A straight line

4. An ellipse

Cyclotron frequency does not depend upon

1. Specific charge

2. Speed of revolving particle

3. Magnetic induction

4. Charge

The maximum kinetic energy of an $\alpha -particle$ coming out of a cyclotron accelerator is 20 MeV. The maximum kinetic energy of a proton that can be obtained from this accelerator is 

1. 20 MeV

2. 40 MeV

3. 10 MeV

4. 5 MeV