A wire of resistivity ρ, length L, area A has resistance R. If length doubled and area halved, new resistance is MCQ with Answer and Explanation

Explanation:
Power = Work/Time. Work has dimensions [ML²T⁻²], dividing by time [T] gives [ML²T⁻³]. Energy is [ML²T⁻²], force is [MLT⁻²], momentum is [MLT⁻¹]. This dimensional formula uniquely identifies power. Memory tip: Power = energy per second ⇒ dimensions include extra T⁻¹ factor. Frequently tested in dimensional analysis sections of competitive exams.

Explanation:
An alpha particle consists of two protons and two neutrons tightly bound together. This is completely identical to the nucleus of a helium atom (He²⁺). Alpha particles are positively charged, relatively massive, have low penetrating power, and are emitted by heavy radioactive elements during alpha decay.

Explanation:
Retina contains rods and cones. Cornea and lens focus, iris controls light.