The S.I unit of heat is

Step 1: Analyze the question The question asks for the S.I. unit of heat. Heat is a form of energy that transfers from a hotter body to a colder one.

Step 2: Explain the concept Since heat is a form of energy, its S.I. unit is the same as the unit of energy: the joule (J).

Let's check why the other options are wrong, because each one is the unit of a different quantity:

• Kelvin (K) is the S.I. unit of temperature, not heat. Students often confuse heat with temperature. Heat is the energy transferred, while temperature measures how hot or cold something is.
• Watt (W) is the unit of power, which is energy per unit time (1 W = 1 J/s).
• Ampere (A) is the unit of electric current.

Step 3: Show the solution The heat energy needed to change the temperature of a substance is:

Q = mcΔθ

Checking the units:

• m in kg
• c (specific heat capacity) in J kg⁻¹ K⁻¹
• Δθ in K

Q = kg × (J kg⁻¹ K⁻¹) × K = J

So heat is measured in joules.

Step 4: Answer The correct option is A. joule.

Step 5: Exam tip Remember: Heat = Energy = Joule, while Temperature = Kelvin. In WASSCE, JAMB, and NECO, examiners love to test whether you can tell apart heat and temperature, and energy and power (joule vs. watt). Match each quantity with its unit and you'll pick up easy marks.