Current carrying wire creates a magnetic field. This magnetic field has no effect on a stationary charge. But when the charge also moves, it creates a current. This current produces a magnetic field. Two fields interact and the charge is deflected. So, the assertion is true. Moving charge creates a current which produces a magnetic field. So, the reason is also true. Reason is the correct explanation of A.

The force on a charged particle moving in a uniform magnetic field always acts in direction perpendicular to the direction of motion of the charge. So work done by the magnetic field, W = FS cos θ = FS cos 90° = 0 So, the energy of the charged particle does not change. Both assertion and reason are true and reason also explains the assertion.

Magnetic field inside a solenoid is B = μ₀ ni. Magnetic field at the end of a solenoid is 1/2 μ₀ ni. So, the assertion is true. Magnetic field within a sufficiently long solenoid is uniform. So the reason is also true. But it does not explain the assertion.

The electric current is defined to be the rate at which charges flow across any cross-sectional area. In the case of metallic rod, the charge carries flow through whole of the cross section. Therefore, the magnetic field exists both inside as well as outside. 
However magnetic field inside the rod will go no decreasing as we go towards the axis.
Hence, the assertion is correct but the reason is incorrect.

The torque on the coil in a magnetic field is given by τ = nIBA sin θ For radial field, θ = 90° and sin θ = 1 Torque = nIBA and it is maximum. So the assertion is true. Torque is the rotational equivalence of force.

So, torque will tend to rotate a coil. Reason is also true. But reason cannot explain the assertion that why the torque is maximum in the specified position.

The coil of the moving coil galvanometer is suspended in a very strong radial magnetic field. Earth’s magnetic field is too weak compared to that and hence its effect is negligible. So, assertion and reason both are true and the reason explains the assertion properly.

A cyclotron is a kind of particle accelerator invented by Ernest O. Lawrence at the University of California, Berkeley, in 1929–1930, and patented in 1932. A cyclotron accelerates charged particles along a spiral path outward from the center. The particles are guided by a static magnetic field to a spiral trajectory, and accelerated by a rapidly changing electric field (radio frequency). For this invention Lawrence received the 1939 Nobel Prize in Physics.

Cyclotrons were the most efficient particle accelerator equipment until the 1950s, when the synchrotron replaced them, and are now used in science and nuclear medicine to generate particle beams.

This will toss the particle out of resonance with the oscillating field which means that when the particle reaches the hole between the dees, the extremity of the dees won't change. Thus, the particle won't be accelerated further.

So, Cyclotron isn't reasonable for accelerating electrons. Because of the small mass, the speed of electrons increments quickly. Similarly, because of fast relativistic variation in their mass, the electrons escape step with the oscillating electric field.

Hence, option A is the correct option.

Magnetic field inside the solenoid at point P is given by, B=μ0/4π (2πni)[sinα+sinβ] Where n=no. of turns per unit length =N/l. Thus it is clear that magnetic field is independent of length and cross sectional area. Also the magnetic field with in the solenoid is uniform and parallel to the axis of the solenoid.

The radius of the circular path is given by

Since K and B are the same for the two particles,

Now, the charge of an alpha particle is twice that of a proton and its mass is four times the mass of a proton, √ m /q will be same for both particles.

Hence, r will be the same for both particles.

In case of the electric dipole, the electric lines of force originate from positive charge and end at negative charge. Since isolated magnetic lines are closed continuous loops extending throughout the body of the magnet