Question

a bulb is rated at 220v-100w. what is the resistance. five such bulbs burn for 5 hours, what is the electrical energy consumed

Answer 1

Hi..

we know that for an electric appliance
P = V² /R
or
 resistance will be given as 
R = V² / P

now, here
P = 100 W
 V = 200 volts

so, R = 200² / 100
= 40000 / 100

thus, resistance of the bulb is R = 400 Ω 

now, electric energy consumed will be
E = number of units x power of each unit x time = n x P x t

here
n = 5 P = 100 W
t = 4 hours
so,
 E = 5 x 100 x 4

thus, E = 2000 Wh = 2 kWh 

the total cost of electricity = total unit of energy consumed x cost per unit = 2kWh x 0.5 Rs/kWh 
thus,
total cost (daily) = Rs. 1
 and
monthly cost = total daily cost x number of days in month
= Rs. 1 x 30 days 
or monthly cost = Rs. 30 ...

Hope this helps u!!

Answer 2

$\huge\fbox\orange{\underline{Question:–}}$

An electric bulb is rated at 200w-100w what is the resistance of 5 such bulbs burn for 4 hours. What is the electrical energy consumed. Calculate the cost if the rate is 50 paise per unit.

$\huge\fbox\orange{\underline{Answer:–}}$

Using, P = $\large{V²}{R}$

we get R = $\large{V²}{P}$

= $\large{(200)²}{100}$

= 400

Energy consumed = P x t

= 100 x 4

= 400 Wh

= 0.4 kWh

Cost at the rate of 50 paise per unit

= Rs (0.50 x 0.4)

= Rs 2

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