3.3 - Measuring Energy Output and Input

Question 1

What is power? What are it’s units/ways of measurement?

Answer 1

• The rate at which a device converts energy from one form to another
• The unit of power is the Watt, which is equal to one joule/second. The faster a device converts electricity, the greater its power rating.

Question 2

What is the formula to calculate power?

Answer 2

Power = Current x Voltage ⟶ P = I x V

Question 3

What is the formula to calculate current?

Answer 3

Current = Power / Voltage ⟶ I = P/V

Question 4

What is the formula to calculate voltage?

Answer 4

Voltage = Power / Current ⟶ V = P/I

Question 5

What is energy?

Answer 5

• The ability to do work
• Power ratings can be used to calculate the amount of energy a device uses
• Measured in joules (watts/second)

Question 6

What is the formula for calculating energy?

Answer 6

Energy = Power x time (in seconds) ⟶ E = P x t

Question 7

What is efficiency?

Answer 7

• The ratio of useful energy produced to the total energy input
• Some of the input energy is converted to “waste” energy such as the light produced inside a toaster

Question 8

What is the formula to calculate efficiency?

Answer 8

%eff = (joules of useful output / joules of input energy) x 100

Question 9

What type of energy is input energy often converted to?

Answer 9

“Waste” energy, such as heat

Question 10

In devices that convert electricity to mechanical energy, what is responsible for creating a lot of waste energy?

Answer 10

In devices that convert electricity to mechanical energy, friction is responsible for creating a lot of waste energy

Question 11

How can efficiency be increased?

Answer 11

• Using better bearings (devices that spin or move better = less friction)
• Using lubricants
• Improving insulation
  
  • Ex. In refrigerators
• Using a capacitor (a device that can store energy in the electric field between a pair of conductors)