Question

A bulb is rated at 200 v- 100 w. what is its resistance? Five such bulbs burn for 4 hours. What is the electrical energy consumed? Calculate the cost if the rate is Rs-4.60 per unit

Answer 1

(1) here we have,
p = 100w
v = 200 v
I = ??
we know that
p = v*I
100 = 200 *i
i = 1/2 anphere
(2) here we have
no of bulb = 5
time taken = 4hr
therefore ,
p = 5*200*0.5 = 500 w or 1/2 kw
electrical energy comsumed = p*t = 1/2 *4 = 2 kWh
( 3) total cost = 2*4.6 = 9.2 rupees

Answer 2

Question :-

• A bulb is rated at 200 v- 100 w. what is its resistance? Five such bulbs burn for 4 hours. What is the electrical energy consumed? Calculate the cost if the rate is Rs-4.60 per unit ?

Answer :-

• Resistance = 400 ohms
• The total electrical consumed is 2 units .
• The cost of electrical energy is Rs 9.20

Given :-

• Voltage = 220 volts
• Power = 100 watts

To find :-

• what is its resistance?
• What is the electrical energy consumed?
• Calculate the cost if the rate is Rs-4.60 per unit ?

Solution :-

(a) Calculation of Resistance.

Now,

we all know the voltage and power of the bulb.

So, the resistance can be calculated by using the formula :

• P = V²/ R

where,

• P = Power
• V = Voltage
• R = Resistance

Now, putting the values in the above formula we get,

↠ 100= ( 200 ) ² / R

↠100 R = 40000/100

↠R = 400 ohms

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(b) Now, we Calculate of Electrical Energy Consumed.

As we all know that

• E = P × t

↠ E = 100 / 1000 kilowatt

↠ E = 0.1 kilowatt

Time = 4 hours ( given )

So,

Energy Consumed by 1 bulb = 0.1 × 4

↠ 0.4 kilowatt - hours

And,

Energy Consumed by 5 bulbs = 0.4 × 5

↠ 2 kWh

hence, the total electrical consumed is 2 units .

____________________________

(c) Now, we find the cost of electrical energy

↠ Cost of 1 unit of electricity = Rs 4.60

So,

↠ Cost of 2 units of electricity = Rs 4.60 × 2

↠ Rs 9.20

Hence, the cost of electrical energy is Rs 9.20

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