A lactometer measures MCQ with Answer and Explanation

Explanation:
While James Clerk Maxwell predicted electromagnetic waves mathematically, it was the German physicist Heinrich Hertz who successfully built the first spark-gap transmitter in 1887. He physically generated and detected radio waves in his laboratory, proving Maxwell's theories right. The SI unit of frequency, the Hertz (Hz), is named in his absolute honor.

Explanation:
Measures specific gravity of milk, indicates adulteration.

Explanation:
From Newton's law: F = Gm₁m₂/r² ⇒ G = Fr²/(m₁m₂). Force F has [MLT⁻²], r² has [L²], m₁m₂ has [M²]. Thus G = [MLT⁻²][L²]/[M²] = [M⁻¹L³T⁻²]. Memory aid: 'G dimensions: [M⁻¹L³T⁻²]; small value (6.67×10⁻¹¹) reflects weak gravity'. This dimensional analysis question tests ability to derive constants, frequently appearing in competitive exams. Always verify by substituting into fundamental equations; dimensional consistency is a powerful tool for error checking in physics problems.