Power

Defining Power

  • Power is the rate at which work is done or energy is transferred.
  • It can be calculated using the formula: P = W/t, where P is power, W is work done or energy transferred, and t is time.

Units of Power

  • The unit of power in the International System of Units (SI) is the watt (W).
  • It’s defined as one joule per second (J/s).

Calculating Power

  • Another formula to calculate power when dealing with mechanical energies is P = Fd/t, where P is power, F is force, d is displacement, and t is the time taken.
  • Here, Fd represents the work done.

Power and Energy Efficiency

  • Efficiency is the proportion of the input power that is successfully converted to useful output power. It is expressed as a percentage.
  • It can be calculated as: efficiency (%) = (useful power output / total power input) x 100.
  • In an energy transformation, some energy is usually converted into unwanted forms, often thermal energy due to friction. This wasted energy reduces efficiency.
  • No device or machine is 100% efficient due to these energy losses.

Power in Electrical Systems

  • In electrical systems, power can be also calculated using the formula P=IV, where P is power, I is current, and V is voltage.

Power and Velocity

  • When dealing with objects in motion, power can be calculated using the formula P = Fv, where P is power, F is the force, and v is the velocity of the object.
  • Here, Fv represents the work done per unit time.