Energy Formulas
Energy is the capacity to do work or to transfer heat. Power is energy flow -- it is the change in energy per unit change time. Power is the differential of energy, and energy is the integral of power. Energy can neither be created nor destroyed, it can only be transformed.
Apparent power: The product of the voltage (in volts) and the current (in amperes). It comprises both active and reactive power. It is measured in “volt-amperes” and often expressed in “kilovolt-amperes” (kVA) or “megavolt-amperes” (MVA).
Calorie: The amount of energy needed to raise the temperature of 1 gram of water by 1°C.
kilogram calorie -- One Cal can raise the temperature of one kilogram of water one degree Celsius (°C)
The kilogram (kg) is the unit of mass; it is equal to the mass of the international prototype of the kilogram. It is essentially the mass of a liter of water at 4°C.
Horsepower: In measuring power Horsepower is a unit which is in common use. However in physics we use Watt. So the first thing to do in solving any problem related to power is to convert horsepower to Watts. 1 horsepower (hp) = 746 Watts
Joule (J), a measure of energy, is 1 newton-meter of work. It is also equal to 1 watt-second of energy. There are 3.6 megajoules in a kilowatt-hour. To raise a liter of water one meter is about 9.8 joules of work.
Ohm is the electrical resistance of a uniform column of mercury at 0°C, 106.4 cm in lenght with a mass of 14.4521 g. A current of 1 ampere though a resistance of 1 ohm disapates a power of 1 watt.
Ohm's Law: Power (watts) P = I × V = I2 x R = V2 ⁄ R
Power (P) is work( W) done in unit time (t). P = W/t as work and energy (E) are same it follows that power is also energy consumed or generated per unit time.
Power (watts) =Energy transfered (joules) / Time (seconds
Power Factor: The cosine of the phase angle between voltage and current in an AC circuit. The power factor is the difference between real power (watts used) and the apparent power (volts x amps) in a circuit. The cosine of 90 degrees = 0. If the angle between the current and voltage in a circuit equals 90 degrees, then the power in watts would be 0. Ex: (110-volts AC x 10 amps) x (cosine 90) = 0 watts. There is no such thing as a power factor for DC ciruits.
Thermal Energy One measure of heat energy is the BTU (British Thermal Unit). A BTU is the energy that goes into heating one pound of water one degree Fahrenheit. Amazingly, this is the equivalent of 778 ft-lbs of work. In other words, the thermal energy that goes into raising the temperature of an 11 ounce mug of coffee one degree (°F) is approximately equivalent to the work of lifting 55 pounds up one flight of stairs. (A pint , or 16 fluid ounces of water weighs about one pound. Rule of thumb -- A pint’s a pound the world around.)
Volt (V) is the electrical potential across a 1 ohm resistance through which flows a current of 1 ampere.
Watt (W), a measure of power, is one joule per second or one newton-meter per second. The power needed to raise a liter of water one meter in one second is about 9.8 watts. One ampere through an electrical resistance of one ohm develops an EMF of one volt and dissipates one watt of power.
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