Question

ASSERTION:
The magnetic field at the ends of a very long current carrying solenoid is half of that at the centre.
REASON:
If the solenoid is sufficiently long, the field within it is uniform.
(1) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
(2) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
(3) Assertion is correct but Reason is incorrect
(4) Both Assertion and Reason are incorrect

Answer 1

Solenoid is a coil of wire usually in cylindrical form that when carrying a current acts like a magnet so that a movable core is drawn into the coil when a current flows and that is used especially as a switch or control for a mechanical device (such as a valve).

Complete answer: The magnetic field at the ends of a very long current carrying solenoid is half of that at the centre, that is. ${B_{end}} = \dfrac{1}{2}{B_{in}}$
Also for a long solenoid, the magnetic field is uniform within it but this reason is not explaining the assertion.
It is true only for an infinitely long solenoid. Magnetic field at any point is the summation of magnetic fields produced by each turn of the wire of the solenoid. The field at this end is now due to half the total turns and hence it is E/2.

Note The definition of a magnetic field is a place in space near a magnet or an electric current where a physical field is created from a moving electric charge that creates force on another moving electric charge. An example of a magnetic field is the Earth's magnetic field. The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in the Earth's outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo.