Assertion(A): When a wire is stretched to twice its length, its resistance becomes 4 times. 

Reason (R): Resistance is directly proportional to the length of the wire.

Assertion(A): When a current is passed through a solenoid coil, magnetic field is produced around and within the solenoid.

Reason (R): Magnetic field within the current carrying solenoid is uniform.

Assertion(A): The least distance of distinct vision is 25 cm from the eyes. Any object placed closer than 25 cm will appear blurry.

Reason (R): For distance closer than 25 cm, eye lens cannot adjust its power.

Assertion(A): Magnetic field is strongest near the pole of a bar magnet.

Reason (R): The relative strength of magnetic field  is given by the degree of closeness of the field lines.

Assertion(A): White light is a mixture of light of seven colors.

Reason (R): White light when pass through a convex lens of large focal length, it splits into its constituents seven colors.

Assertion(A): A lens of power -2D has more diverging power than a lens of power -4D.

Reason (R): Power of a lens is defined as the reciprocal of its focal length.

Assertion(A): Electric current through a conductor is said to be 1 ampere if \( 6.25\times 10^{18}\) electrons flow through a cross-section of the conductor in 1 second.

Reason (R): The charge of an electron is \( 1.6\;\times 10^{-19}\;C\).

Assertion(A): Resistance of a conductor is given by the ratio of potential difference applied across its ends and the current flowing through it.

Reason (R): Resistance of a conductor depends on the nature of its material, length and its area of cross-section.

Assertion(A): Shorter the focal length of a lens, more is its converging / diverging power. 

Reason (R): Power of a lens is defined as the reciprocal of its focal length.

Assertion(A): Outside a magnet, field lines start from S-pole and end at N-pole of a magnet.

Reason (R): The direction of the magnetic field at a point is given by the direction that a north pole of a compass placed at that point would take.