• The efficiency of a system is a measure of how well energy is transferred in a system
• Efficiency is defined as:

The ratio of the useful power or energy transfer output from a system to its total power or energy transfer input

• If a system has?high?efficiency, this means most of the energy transferred is?useful
• If a system has?low?efficiency, this means most of the energy transferred is?wasted
• Determining which type of energy is useful or wasted depends on the system
  • When electrical energy is converted to light in a lightbulb, the light energy is?useful?and the heat energy produced is?wasted
  • When electrical energy is converted to heat for a heater, the heat energy is?useful?and the sound energy produced is?wasted

• Efficiency is represented as a percentage, and can be calculated using the equation:

• The energy can be of any form e.g. gravitational potential energy, kinetic energy
• The efficiency equation can also be written in terms of power:

• Where power is defined as the energy transferred per unit of time

Step 1: Write down the efficiency equation?

Step 2: Rearrange for the power input??

Step 3: Calculate the power output

• • The power output is equal to energy ÷ time
  • The electric motor transferred electric energy into gravitational potential energy to lift the load

Gravitational potential energy =?mgh?= 7.2 × 9.81 × 5 = 353.16 J

Power = 353.16 ÷ 3 = 117.72 W

Step 4: Substitute values into power input equation?

• The pump is what converts the water’s?kinetic energy?into?gravitational potential energy
• Since its efficiency is 20%, the kinetic energy can be multiplied by 0.2 since only 20% of the?kinetic energy?will be converted (not?20% of the gravitational potential energy)