Question

An electric bulb is rated at 200V , 100W. What is its resistance?

Also calculate the energy consumed by 3 such bulbs if they glow continuously for 10 hours for complete month of November.​

Answer 1

✬ Resistance = 400 ohms ✬

✬ Energy = 9 units ✬

Explanation:

Given:

• Voltage is 200V.
• Power of bulb is 100W.

To Find:

• What is resistance ?

Formula to be used:

• Power = V²R

Solution: Here we have

• P = 100 W
• V = 200
• R = ?

Substituting the values on the formula

$\implies{\rm }$ 100 = 200²/R

$\implies{\rm }$ 100 × R = 40000

$\implies{\rm }$ R = 40000/100

$\implies{\rm }$ R = 400 ohms

Hence, resistance is 400 ohms.

[ For second part ]

Given:

• Number of bulbs is 3.
• Time is 10 hours per day.
• Total days is 30. (November)

To Find:

• Energy consumed by 3 bulbs ?

Formula to be used:

• Energy = Power × time

Solution: Here we have

• P = 100 W
• T = 10 × 30 days
• E = ?

Substituting the values on the formula

$\implies{\rm }$ E = 100 × 10 × 30

$\implies{\rm }$ E = 30000 Wh

So energy consumed by 1 bulb is 30000 Wh.

• Energy consumed by 3 such bulbs = 3 × 30000 = 90000 Wh

• 1000 kWh = 1 Wh
• 90000 Wh = 90000/1000 = 9 kWh.

Hence, energy consumed by 3 bulbs will be 9 kWh or 9 units.

Answer 2

 Resistance = 400 ohms 

 Energy = 9 units 

Explanation:

Given:

Voltage is 200V.

Power of bulb is 100W.

To Find:

What is resistance ?

Formula to be used:

Power = V²R

Solution: Here we have

P = 100 W

V = 200

R = ?

Substituting the values on the formula

\implies{\rm }⟹ 100 = 200²/R

\implies{\rm }⟹ 100 × R = 40000

\implies{\rm }⟹ R = 40000/100

\implies{\rm }⟹ R = 400 ohms

Hence, resistance is 400 ohms.

[ For second part ]

Given:

Number of bulbs is 3.

Time is 10 hours per day.

Total days is 30. (November)

To Find:

Energy consumed by 3 bulbs ?

Formula to be used:

Energy = Power × time

Solution: Here we have

P = 100 W

T = 10 × 30 days

E = ?

Substituting the values on the formula

\implies{\rm }⟹ E = 100 × 10 × 30

\implies{\rm }⟹ E = 30000 Wh

So energy consumed by 1 bulb is 30000 Wh.

Energy consumed by 3 such bulbs = 3 × 30000 = 90000 Wh

1000 kWh = 1 Wh

90000 Wh = 90000/1000 = 9 kWh.

Hence, energy consumed by 3 bulbs will be 9 kWh or 9 units.