# Physics question? [info in the description]

## An establishment receives electric energy @ Rs 4.50 per kWh at a p.d of 240 V. It uses the following appliances : (i) 20 tubelights of 40 W each working 10 hrs a day (ii) 2 stereo systems each drawing a current of 2 A and working 4h a day (iii) 4 ovens each of resistance 24 ohm working 6 hrs a day (iv) 2 cooling machines of 4 H.P. each working 15 hrs a day. CALCULATE : (a) monthly bill (b) minimum fuse rating of circuit ? ( PLS ANS URGENTLY EXPERTS , I REQUEST YOU )

Dec 30, 2016

The monthly bill is Rs 21 459.60 (based on a 30-day month), with a total current draw of 72.2 A.

#### Explanation:

A fair bit of work to do. We will tackle it one step at a time.

i) 20 lights at 40 W each = 800 W
800 W x 10 hrs = 8000 Wh = 8 kWh

ii) $P = I \times V$
(each stereo) 2A x 240 V = 480 W x 2 stereos = 960 W
960 W x 4hrs = 3840 Wh = 3.84 kWh

iii) $P = {V}^{2} / R$
(each oven) $P = {240}^{2} / 24 = 2400 W \times 4 \text{ ovens} = 9600 W$
9600 W x 6 hrs = 57 600 Wh = 57.6 kWh

iv) 4 hp x 746 W/hp = 2984 W x 2 machines = 5968 W
5968 W x 15 hrs = 89 520 Wh = 89.52 kWh

Add all this power together: 158.96 kWh each day
Taking a month as 30 days, this comes to 4768.8 kWh each month
4768.8 x R 4.50 = R 21 459.60 as the monthly bill.

As for the fuse rating, are we to consider each of (i) through (iv) as a separate circuit? I'm not clear on this point.
Here is what you do:
start with the power consumption in each circuit and divide by the voltage (240). This will give the current that the circuit carries.
i) 3.33 A
ii) 4 A
iii) 40A (although it is likely that each oven would be on a separate 10 A circuit in an actual workplace)
iv) 24.87 A (again, it is likely that each cooling machine operates on a separate circuit, drawing 12.44 A each)

Total current draw: 72.2 A

I haven't specified the fuse requirements, but I hope this can be determined from the current loads.