It takes $12$ minutes to boil $1$ litre of water in an electric kettle. Due to some defect it becomes necessary to remove $20 \%$ turns of heating coil of the kettle. After repair, how much time will it take to boil $1$ litre of water.
AIIMS 2019, Diffcult
Download our app for free and get started
The amount of heat generated is,
$H =\frac{ V ^{2}}{ R } t$ $....(i)$
It is given $20 \%$ heat is heat to be ejected, thus, the resistance is reduced by $20 \%$
The new resistance is,
$R ^{\prime}= R -0.2 R =0.8 R$
The new amount of heat generated is,
$H ^{\prime}=\frac{ V ^{2}}{0.8 R } t ^{\prime}$ $....(ii)$
On equating both equations $(i)$ and $(ii)$ we get,
$\frac{ V ^{2}}{ R } t =\frac{ V ^{2}}{0.8 R } t ^{\prime}$
$t ^{\prime}=0.8 \times t =0.8 \times 12 min =9.6 min$
Download our appand get started for free
Experience the future of education. Simply download our apps or reach out to us for more information. Let's shape the future of learning together!No signup needed.*
Similar Questions
- 1A wire of resistance $20 \Omega$ is divided into $10$ equal parts. A combination of two parts are connected in parallel and so on. Now resulting pairs of parallel combination are connected in series. The equivalent resistance of final combination is_______.0$\Omega$.View Solution
- 2A battery consists of a variable number '$n$' of identical cells having internal resistances connected in series. The terminals of battery are short circuited and the current $i$ is measured. Which of the graph below shows the relation ship between $i$ and $n$View Solution
- 3Current $I$ in the network shown in figure is .......... $A$View Solution
- 4For a cylinder of radius $R$ current density $J =J_0 \frac{r}{R} $, where $J_0$ is a constant and $r$ is distance from axis. Calculate total currentView Solution
- 5Assertion : All electric devices shown in the circuit are ideal. The reading of each of ammeter $(a)$ and voltmeter $(V)$ is zero.View Solution
Reason : An ideal voltmeter draws almost no current due to very large resistance, and hence $(V)$ and $(a)$ will read zero.
- 6In the circuit shown, $R_1$ is increased. What happens to the reading of the voltmeter (ideal)?View Solution
- 7A hot electric iron has a resistance of $80\,\Omega $ and is used on a $200\, V$ source. The electrical energy spent, if it is used for two hours, will be ........... $Wh$View Solution
- 8Find potential at point $C$ and $D$View Solution
- 9Four resistances are connected in a circuit in the given figure. The electric current flowing through $4\, ohm$ and $6\, ohm$ resistance is respectivelyView Solution
- 10View SolutionResistance of one carbon filament and one tungsten lamp are measured individually when the lamp are lit and compared with their respective resistances when cold. Which one of the following statements will be true