How is the calorific value of a fuel expressed?

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Explanation

Calorific value is defined as the amount of heat energy released when a unit mass of a fuel is completely burned.
The standard international (SI) unit for energy is the Joule (J). For larger quantities, the Kilojoule (kJ) is used.
The standard unit for mass is the kilogram (kg).
Combining these, the unit for calorific value (energy per mass) becomes Kilojoules per kilogram (kJ/kg).

Option B: Kilometer per kg is a unit of distance per unit mass. It has no relation to energy or heat.
Option C: A kilonewton is a unit of force. Kilonewton per kg is a unit of force per unit mass, which is equivalent to acceleration (since F=ma, a=F/m). It does not measure heat energy.
Option D: A kilowatt is a unit of power, which is the rate at which energy is used or transferred (Joules per second). Kilowatt per kg would represent power per unit mass, not the total energy content.

Visual 1: Diagram - An illustration showing a 1 kg block of fuel (e.g., wood or coal) on a scale, with an arrow pointing to a flame and another arrow showing heat energy being released, labeled with 'Kilojoules (kJ)'. This visually connects the concepts of mass (kg) and energy (kJ).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Unit of Calorific Value as background academic context rather than a clinical decision trigger.
While this question concerns fuel, the underlying concept of energy units is vital in nursing for nutrition and dietetics.
The energy value of food is measured in kilocalories (kcal) or kilojoules (kJ), which nurses use to calculate patients' dietary needs, assess nutritional status, and plan interventions.
Understanding the difference between energy (kJ) and power (kW) is crucial. For example, a patient's total daily energy requirement is in kJ or kcal, while the rate at which they expend energy during an activity could be considered in terms of power.

How to Approach the Question

First, identify the key term in the question: 'calorific value'.
Recall or deduce the definition of this term. Calorific value is the energy contained per unit mass of a substance.
Break this definition down into its fundamental physical quantities: 'Energy' and 'Mass'.
Identify the standard units for these quantities. Energy is measured in Joules (or Kilojoules), and mass is measured in kilograms.
Combine the units according to the definition: Energy / Mass → Kilojoules / kg.
Scan the options to find the one that matches your derived unit, which is 'Kilojoules per kg'.

Concept Tested & Keywords

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Practise the full RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Attempt every question from this paper in a timed mock, then review the full solution for each one.