Question

If 1 unit of electricity cost $0.20$, how much does it cost to switch on a heater marked $120V$, $3A$ for $90$ min?

• A. $0.11$
• B. $2.70$
• C. $64.80$
• D. $108.00$

Answer 1

Answer: (A)

$0.11$

Voltage across the heater $V=.12$ kilo-volts

Current flowing through the heater $I=3A$

Thus power of the heater $P=VI$

$\therefore$ $P=0.12\times 3=0.36$ $kW$

Time of operation $t=90$ min $=1.5$ hr

Thus energy consumed $E=Pt$

$⟹$ $E=0.36\times 1.5=0.54$ $kWhr$

Cost to switch on heater = $0.54\times 0.2=0.11$