Question

Bulb is rated at 200 V, 100 W. Calculate its resistance. Five such bulbs are lighted for 4 hours daily. Calculate the units of electrical energy consumed per day. What would be the cost of using these bulbs per day at the rate of Rs. 4.00 per unit?

Answer 1

Answer:

1.6

Explanation:

We know that for an electric appliance   p=(v^2)/R

Resistance will be given as   R=(v^2)/p

Now, here  

P = 100 W

V = 200 volts

Thus, resistance of the bulb is R = 400 Ω  

Now, electric energy consumed will be  

E = power of each unit × time.

⇒ E = p × t.  

Here  

P = 100 W  

t = 4 hours  

So,  

E = 100 x 4 = 400 Watt per hour  

Dividing by 1000 to convert into Kilo Watt per hour

E = 0.4 kWh  

Electrical energy consumed is 0.4 kWh  

The total cost of electricity = total unit of energy consumed x cost per unit =

Cost = 0.4kWh x 4 Rs/kWh = Rs1.6  

Thus, total cost (daily) = Rs. 1.6

Answer 2

Electricty charges for the bulb per day = Rs. 1.60

Explanation:

For an electric circuit, we know that P = V²/R

So R = V²/P

Given P = 100 W and V = 200 V,

So R = 200 * 200 / 100 = 400 Ohms.

Resistance of the bulb = 400 Ohms.

Energy consumed by the bulb = Power of each unit * time = 100 * 4 = 400 Watts per day

Converting to Kilowatts, 400 Watts = 0.4 kWh.

Cost of one unit = Rs. 4

Cost of 0.4 units = 0.4 * 4 = Rs. 1.60