Beta rays emitted by radioactive substances are essentially: MCQ with Answer and Explanation

Explanation:
Thermal radiation is the transfer of heat via electromagnetic waves (primarily infrared). Unlike conduction (which requires physical contact) or convection (which requires fluid movement), radiation can travel through a vacuum. This is how the heat from the Sun reaches the Earth through the vacuum of space.

Explanation:
Centripetal force acts radially inward, perpendicular to tangential displacement. Work W = F·d·cosθ; θ=90° ⇒ cos90°=0 ⇒ W=0. No energy transfer occurs; speed remains constant in uniform circular motion. Memory tip: 'Perpendicular force ⇒ zero work'. Conceptual question testing work-energy understanding, common in competitive exams to identify misconceptions about circular motion.

Explanation:
In uniform circular motion, speed remains constant but direction changes, so velocity (vector) changes. There is centripetal acceleration towards centre, so acceleration is not zero. Kinetic energy = ½mv², depends on speed, so remains constant. Thus, only speed is constant.