Question: Which does not have the same unit as others: [PMT/NEET-2004]
a. Watt–sec
b. Kilowatt–hour
c. eV
d. J–sec

Answer: The correct answer is: d. J–sec

Explanation:

• Watt–sec: 1 Watt = 1 Joule/sec. So Watt–sec = Joule. This is a unit of energy.
• Kilowatt–hour: 1 kW·h = 1000 Watt × 3600 sec = 3.6 × 10⁶ J. This is also energy.
• eV (electron volt): Energy gained by an electron when it is accelerated through 1 volt potential difference. 1 eV = 1.6 × 10⁻¹⁹ J. Again, this is energy.
• J–sec: This is joule × second, which is the unit of angular momentum or Planck’s constant, not energy.

Therefore, J–sec does not have the same unit as the others.