Advertisements
Advertisements
Question
An electric bulb is rated as 100W – 250V. What information does it convey? Calculate the current through the filament of the bulb.
Advertisements
Solution
Given: P = 100 W, V = 250 volt
The current through the filament, I = `"P"/"V" = 100/250 = 0.4` A.
RELATED QUESTIONS
Define watt-hour. How many joules are equal to 1 watt-hour?
Calculate the cost of operating a heater of 500 W for 20 hours at the rate of Rs 3.90 per unit.
When an electric lamp is connected to 12 V battery, it draws a current of 0.5 A. The power of the lamp is:
(a) 0.5 W
(b) 6 W
(c) 12 W
(d) 24 W
The table below shows the current in three different electrical appliances when connected to the 240 V mains supply:
| Appliance | Current |
| Kettle | 8.5 A |
| Lamp | 0.4 A |
| toaster | 4.8 A |
- Which appliance has the greatest electrical resistance? How does the data show this?
- The lamp is connected to the main supply by using a thin, twin-cored cable consisting of live and natural wires. State two reasons why this cable should not be used for connecting the kettle to the mains supply.
- Calculate the power rating of the kettle when it is operated from the 240 V mains supply.
- A main takes the kettle abroad where the mains supply is 120 V. What is the current is the kettle when it is operated from the 120 V supply?
1Kwh =`( 1 "volt "xx 1 am pere xx.............)/1000`
Fig . shows the essent ial features of a battery operated bell. The hammer strikes the gong when the swi tch is closed . State and explain the effect of using the following material successively to form the core.

(a) Plastic
(b) Steel
(c) Copper
Why is the electric power from the generating station transmitted at high voltage?
Compare the power used in the 2 Ω resistor in each of the following circuits:
- a 6 V battery in series with 1 Ω and 2 Ω resistors
- a 4 V battery in parallel with 12 Ω and 2 Ω resistors.
