Advertisements
Advertisements
Question
What is the resistance, under normal working conditions, of an electric lamp rated at '240 v, 60 W' ? If two such lamps are connected in series across a 240 V mains supply, explain why each one appears less bright.
Advertisements
Solution
Given voltage, V = 240 V
Power, P = 60 W
As P = `"V"^2/"R"`
∴ R = `(240)^2/60`
= 960 Ω
I = `"P"/"V"` = 0.25 A
When one lamp is connected across the mains, it draws 0.25 A current, while if two lamps are connected in series across the mains, current through each bulb becomes
`(240 "V")/((960 + 960) Omega) = 0.125 "A"`
(i.e., current is halved), hence heating (= I2Rt) in each bulb becomes one-fourth, so each bulb appears less bright.
APPEARS IN
RELATED QUESTIONS
In a household electrical circuit, the appliance are connected in ............with the mains.
If out of the two lighted bulbs in a room, one bulb suddenly fuses, then
From where does the electricity come to our home ?
If an appliance of power P watt is used for time t hour. How much electrical energy is consumed in kWh?
What is an electric fuse? State its purpose in the household electrical circuit.
Assuming the electric consumption per day to be 12 kWh and the rate of electricity to be? 6.25 per unit, find how much money is to be paid in a month of 30 days?
In a premise 5 bulbs each of 100 W, 2 fans each of 60 W, 2 A.Cs each of 1.5 kW is used for 5 h per day. Find:
- Total power consumed per day,
- Total power consumed in 30 days,
- Total electrical energy consumed in 30 days.
- The cost of electricity at the rate of ₹ 6.25 per unit.
State and define the household unit of electricity.
Two bulbs are rated 60 W, 220 V and 60 W, 110 V respectively. Calculate the ratio of their resistances.
Sumit does 600 J of work in 10 min and Amit does 300 J of work in 20 min. Calculate the ratio of the powers delivered by them.
