Question

An electric bulb is rated 220v-100w.what is its resistance? Five such bulbs burn for 4 hours what is its electric energy consumed?calculqte the cost if the rate is 50 paise percl unit

Answer 1

Given data : An electric bulb is rated 220 v and 100 w. Five such bulbs burn for 4 hours.

To find :

• what is its resistance ?
• what is its electrical energy consumed ?
• calculate the cost if rate is 50 paise per unit.

Solution : We know that basic formula for electric appliances,

⟹ P = V²/R

⟹ R = V²/P

where,

• R is resistance
• P is power
• V us potential difference/voltage

Now, a/c to give. data

• P = 100 w
• R = ?
• V = 220 v

By formula,

⟹ R = V²/P

⟹ R = (220)²/100

⟹ R = 48400/100

⟹ R = 484 ohm

Now, we have to find the consuming of electric energy in hour,

Time = 4 hour = 4 * 3600 sec = 14400 sec

• Electric energy = power * time
• Electric energy = 100 * 14400
• Electric energy = 1440000
• Electric energy = 1.44 * 10⁶ joule

Here, we know

• 1 kWh = 3.6 * 10⁶ joule

Now we have to find out energy consumed by each bulb,

⟹ energy consumed by each bulb in unit = Electric energy/3.6 * 10⁶

⟹ energy consumed by each bulb in unit = 1.44 * 10⁶ /3.6 * 10⁶

⟹ energy consumed by each bulb in unit = 0.4 kWh

Now,

⟹ per unit cost of electricity = energy consumed by each bulb in unit * cost per unit

⟹ per unit cost of electricity = 0.4 * 50

⟹ per unit cost of electricity = 20 paise

Now,

⟹ per unit cost of electricity 5 bulb = per unit cost of electricity * 5

⟹ per unit cost of electricity 5 bulb = 20 * 5

⟹ per unit cost of electricity 5 bulb = 100 paise

⟹ per unit cost of electricity 5 bulb = Rs 1

Answer : Resistance of the bulb is 484 ohm. Electric energy consumed by each bulb in unit is 0.4 kWh. Cost of electricity of each bulb is 20 paise.