Energy Sciences

CONTENTS OF CURRICULUM UNIT 13.05.06

  1. Unit Guide
  1. Introduction
  2. An Ancient use of Energy
  3. Two Types of Energy
  4. Nuclear Power – Nuclear Energy
  5. Solar Energy
  6. Units of Energy
  7. Lesson Plans and Activities
  8. Notes
  9. Bibliography
  10. Appendix on Implementing District Standards

Math Equations of Energy

Luis Alberto Magallanes

Published September 2013

Tools for this Unit:

Units of Energy

The most significant measures for the purpose of solar energy are the intensity and the energy delivered. One of these measures relates to "At point in time," while the other one is related to "Over a period of time." Irradiance in Watts per square meter and power in Watts represents the intensity at a point in time. Over a period of time, energy per unit area, Kilowatt-hour per square meter, represents the energy.

The unit that is commonly used to measure the amount of energy is the same as the one used to measure the amount of work. In the international system (SI), this unit is the joule, in honor of the English physicist James Prescott Joule for his work on the mechanical equivalent of heat. Joule's work led to the theory of conservation of energy: "Energy cannot be created or destroyed, it can only be transformed."

A joule

Previous to defining what a joule is, I will define what a newton is. The name of the unit is given to honor Sir Isaac Newton for his studies in classic mechanics. It is important to mention that the unit is spelled in English starting with a lower case "n." A newton is the amount of force used to move an object with a mass of 1 Kg, a distance of 1 meter, in one second, reaching a speed of 1 m/second, starting from rest.

A joule is the amount of energy needed to move one meter of distance an object with a mass of 1 Kg, in one second, reaching the speed of 1 m/second, starting from rest. For electricity, one joule is the amount of energy used in passing an electric current of one ampere through a resistance of one ohm for one second.

1 joule is equal to the following:

1×10 7ergs (exactly), 6.24150974×10 18eV (electron volts), 0.2390cal (thermochemical gram calories or small calories), 2.3901×10 −4kcal (thermochemical kilocalories, kilogram calories, large calories or food calories), 9.4782×10 −4BTU (British thermal unit), 0.7376ft-lb (foot-pounds), 2.7778×10 −7kilowatt-hour, 2.7778×10 −4watt-hour, 9.8692×10 −3liter-atmosphere, 11.1265 femtograms (mass-energy equivalence), 1×10 −44foe (exactly). One femtogram is equal to 1.0 x 10 –18 Kg.

Units defined exactly in terms of the joule are:

1 kilowatt hour = 3.6×10 6j (or 3.6 Mj), 1 watt second = 1j, 1 watt hour = 3600 j, 1 ton TNT = 4.184 Gj, 1 thermochemical calorie = 4.184 j

Thermodynamic Limit on Efficiency of a Heat Engine

Efficiency equation = 1 – Tcold/T hot

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