Question

Suppose an electric toaster oven is on for 30 minutes. Roughly (to 30% accuracy) how much energy is used by the oven? (a) 5 kWh (b) 3.6 MJ (c) 5 Wh (d) 2 million Joules

Answer 1

Answer:

Roughly, an electric toaster oven on for 30 minutes uses: d) 2 million Joules of energy

Explanation:

An average toaster oven uses around 1.2 kW (or 1200 W) of power.

If it is on for 30 minutes, we can calculate how much energy it will use, knowing that energy equals power times time (that the machine is using power), taking into account units (kWh=kW*h and J=W*s):

$E_{kWh}=1.2kW*30 min*\frac{1 h}{60 min}=0.6kWh\\E_{J}=1200W*30 min*60\frac{s}{min}=2160000 J$

As we assumed the power of the toaster, it is enough to say that an electric toaster oven uses roughly 2 million Joules, as there is only an 8% ($\frac{|difference between values|}{value used} *100=\frac{|160000 J|}{2000000J} *100$) difference between our calculated value and the rough estimation.