Question

a bulb is rated at 330V-110W. what do you think is its resistence? three such bulbs burn for 5 hrs at a stretch. what is the energy consumed? calculate the cost in rupees if the rate is 70 paise per unit

Answer 1

Explanation:

We have to find the resistance of bulb first, so

We have to find the resistance of bulb first, soA/c to formula of power

P=V^2/R

.•. R=V^2/P

R=330×330/110

R=990ohm

Resistance of bulb is 990 ohms

Now energy used by one bulb

E=Pt

= 110×5 Wh

= 550Wh

Total energy consumed by 3 bulbs

Total energy= 3×550 Wh

= 1650 Wh

1 unit = 1kWh= 1000 wh

Total unit= 1650/1000

= 1.65 kWh

₹1=100 paise

70 paise= 70/100

=₹0.7

Now total amount

=₹0.7× 1.65

=1155/1000

= 1.155

Answer 2

Answer:

Resistance of 1 bulb = 990Ω

Total cost of energy consumed = Rs 1.155

Explanation:

Power = $\rm\frac{Work \: \: Done}{ Time}$

Work Done = Energy

Therefore ,

Power = $\rm\frac{Energy}{ Time}$

Energy = VIt

Time = t

Power = $\rm\frac{V \: I \: \cancel{t}}{ \cancel{t}}$

Power = VI

According to the question ,

V = 330 V

P = 110 W

t = 5 hrs

Number of bulbs = 3

Cost of 1 unit of Energy = 70 paise

P = VI

I = P/V

I = $\rm{\frac{ \cancel{110}}{ \cancel{330} } \: A}$

I = $\rm \frac{1}{3} \: A$

By Ohm's Law

V = IR

R = V/I

R = $330 \div \frac{1}{3}$ Ω

R = $330 \times 3$ Ω

R = 990 Ω

Therefore , resistance of 1 bulb is 990 Ω .

Energy = VIt

E = VIt

E = $330 \times \frac{1}{3} \times 5$ Wh

E = 550 Wh

Therefore , energy consumed by 1 bulb is 550 Wh .

Energy consumed by 3 bulbs = 3 X Energy consumed by 1 bulb

Energy consumed by 3 bulbs = 3 X 550 Wh

Energy consumed by 3 bulbs = 1650 Wh

1 kWh = 1000 Wh

1 Wh = $\frac{1}{1000}$ kWh

1650 Wh = $\frac{1650}{1000}$ kWh

1650 Wh = 1.65 kWh

Therefore , energy consumed by 3 bulbs is 1650 Wh or 1.65 kWh .

1 Rupee = 100 paise

1 paise = $\frac{1}{100}$ Rupee

70 paise = $\frac{70}{100}$ Rupee

70 paise = Rs 0.7

Cost of 1 unit of Energy = Rs 0.7

Cost of 1 kWh of Energy = Rs 0.7

Cost of 1.65 kWh of Energy = Rs 0.7 X 1.65

Cost of 1.65 kWh of Energy = Rs 1.155