Advertisements
Advertisements
Question
Water in an electric kettle connected to a 220 V supply took 5 minutes to reach its boiling point. How long will it take if the supply voltage falls to 200 V?
Advertisements
Solution
P = `"V"^2/"R"`
Heat gained = `("V"^2)/"R" xx "t"`
`("V"_1^2/"R") xx "t"_1 = ("V"_2^2/"R") xx "t"_2`
t2 = `("V"_1/"V"_2)^2 xx "t"_1`
`= (220/200)^2 xx 300 = 363 "s"`
= 6.05 min
APPEARS IN
RELATED QUESTIONS
Which of the following terms does not represent electrical power in a circuit?
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
Explain why, filament type electric bulbs are not power efficient.
A current of 0.2 A flows through a wire whose ends are at a potential difference of 15 V.
calculate:
(i) the resistance of the wire and
(ii) the heat energy produced in 1 minute.
A resistor of resistance R is connected to an ideal battery. If the value of R is decreased, the power dissipated in the resistor will ______________ .
A coil of copper wire is connected to a galvanometer. What would happen if a bar magnet is:
(i) Pushed into the coil with its north pole entering first?
(ii) Held at rest inside the coil?
(iii) Pulled out again?
Why is heating element wound on a long porcelain rod in a room heater.
Name a metal that is used as an electron emitter. Give one reason for using this metal.
Give two precautious that you would take while putting off an electric switch.
