Question

A transistor radio operates by means of a 14 V battery that supplies it with 69 mA current. If the cost of the battery is $3.61 and it lasts for 311 h, what is the cost per kWh to operate the radio in this manner? Answer in units of $/kW

Answer 1

Voltage V= 14 V

Current I = 69mA

Power (W) = Voltage (V) x Current (A)

So

Power W = 14 V * 0.069A

Power W = 0.966W

So 0.966 W = 0.000966 kW

Now Energy (kWh) = Power (kW) x Time (hours)

= 0.000966 kW * 311 hr

E = 0.300426 kWhr

Hence ,the cost per kWh to operate the radio in this manner =   $\frac{\$ 3.61}{0.300426kWhr}$

= $12.0162 \$ /kWhr$

Again   $Cost = 0.08 \$ /kWhr*0.300426 kWhr$

  $Cost = 0.024034\$$