§4 Efficiency

• Natuurkunde
• Middelbare school
• vwo
• Leerjaar 3

Today's lesson

• Whats efficiency 
• Calculations with efficiency, combined with energy. 
• Homework  

The energy flow diagram of an incandescent lamp.

The efficiency indicates the percentage of useful energy. 

light

warmth

Electric energy

It uses five times less energy, but still produces the same amount of light. The efficiency is five times higher than that of the incandescent lamp.

electric energy

electric energy

light

light

energy-saving bulb

Incandescent lamp

warmth

warmth

Calculating efficiency

For sums with energy use the formula with E and with power use P.

of natural gas delivers

of energy

Excercise 

An electric bottle warmer has an output of 80 W. It takes 8.5 min for the temperature of the 200 g water in the baby bottle to rise from 7 °C to 37 °C.

a Calculate the efficiency of the bottle warmer.

 

Answers excercise

Is there any extra explanation needed next week about this subject?

Yes

No

Only extra practice

Another subject

  §4 excercises 1 t/m 5