Advertisements
Advertisements
Question
A family uses a light bulb of 100W, a fan of 100W, and a heater of 1000W, each for 8 hours a day. If the cost of electricity is Rs. 2 per unit, what is the expenditure to the family per day, on electricity?
Advertisements
Solution
Power consumed in watt-hours
= 100 × 8 + 100 × 8 + 1000 × 8
(bulb) (fan) (heater)
= (800 + 800 + 8000) watt-hours
= 9600 watt hour (units)
i.e. Electric energy comsumed in kWh (units)
`= 9600/1000 = 9.6` kWh.
Cost at Rs. 2 per unit or per kWh
= Rs. 2 × 9.6 = Rs. 19.20.
RELATED QUESTIONS
A battery of e.m.f 15 V and internal resistance 2 Ω is connected to two resistors of resistance 4 ohm and 6 ohm joined in series. Find the electrical energy spent per minute in 6 ohm resistor.
What is electric power? State and define its S.I. unit.
What changes in energy occur in an electric heater?
State relative advantages and disadvantages of ring system of wiring over the tree system.
What is the resistance of an appliance rated at V volt, P watt?
An electric appliance is rated at 1000 W, 250V. Calculate:
(i) The electrical energy consumed by the appliance in 12 hour.
(ii) The cost of energy consumed at Rs. 1.20 per kWh.
How long would this appliance take to use 1 kWh energy when operated at 250 V?
The following table gives the electrical appliances used, their power and the average time for which they are used each day in a home. Estimate the monthly electricity bill if the rate is 60 paise per unit.
| Sr.no. | Name | Nos. | Power rating | Time/day |
| 1 | Bulb | 4 | 100 W | 7.5 hr |
| 2 | Fans | 2 | 50 W | 10 hr |
| 3 | T.V. | 1 | 100 W | 2 hr |
| 4 | Iron | 1 | 500 W | 1 hr |
| 5 | Electric stove | 1 | 750 W | 2 hr |
A torch bulb is rated at 3 V and 600 mA. Calculate it’s
- power
- resistance
- energy consumed if it is used for 4 hours.
An overhead tank of capacity 10 k litre is kept at the top of building 15 m high. Water falls in tank with speed 5`sqrt2` m/s. Water level is at a depth 5 m below ground. The tank is to be filled in `1/2` hr. If efficiency of pump is 67.5% electric power used is ______ W.
