Planck's relation E = hν

Steps:

• Identify units of h: J s (energy × time).
• Recall Planck's formula: E = hν, so h = E / ν (ν is frequency in s⁻¹).
• Verify units for A: ΔE (J) / ν (s⁻¹) = J s, matches h.
• Eliminate others by unit mismatch.

Why A is correct:

• Derives from Planck's quantum hypothesis E = hν, where ΔE is photon energy difference and ν is frequency.

Why the others are wrong:

• B: v (m/s) / D (m) = s⁻¹ (frequency, not J s).
• C: 4πE (electric field in N/C or V/m) yields force/area units, not J s.
• D: F (N) × r (m) / m (kg) = m²/s² (velocity squared, not J s).

Final answer: A