Seven base units: metre, kilogram, second, ampere, kelvin, mole, candela. All other units derived. This is standard definition. Supplementary units radian and steradian now considered dimensionless derived units.
Explanation:
Uranium-235 undergoes fission most efficiently when struck by slow-moving (thermal) neutrons. However, fission reactions release very fast-moving neutrons. The moderator (like graphite or heavy water) collides with these fast neutrons to slow them down without absorbing them, sustaining the controlled chain reaction. Control rods (cadmium/boron) are used to absorb excess neutrons.
Explanation:
Pressure is scalar (no direction), though force is vector. Reason: Pascal's law - fluid pressure transmits equally in all directions, confirming scalar nature. Memory aid: 'Pressure = force/area (scalar division); isotropic in fluids'. Assertion-reason testing fluid mechanics fundamentals, common in competitive exams.
Explanation:
Convection involves bulk movement of fluid particles (liquid/gas). Conduction: vibration transfer without particle movement. Radiation: EM waves. Absorption is taking in heat.
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