Question

A 120 v potential difference is applied to a space heater whose resistance is 17 Ï when hot. (a) at what rate is electrical energy transferred to thermal energy? (b) what is the cost for 7.1 h at us$0.05/kw·h?

Answer 1

a) The rate at which electrical energy is transferred to thermal energy is equal to the power dissipated on the resistor because of the Joule effect:

`P= (V^2)/(R)= ((120 V)^2)/(17 \Omega)=847 W`

b) We can find the total energy dissipated in 7 h:

`E=Pt = (847 W)(7 h)=5929 Wh=5.93 kWh`
The energy costs 0.05 $ per kWh, so the total cost of 5.93 kWh of energy is

`5.93 kW \cdot 0.05 (1)/(kWh) =0.30` $