The battery of a mobile phone is rated as $4.2 \ V, 5800 \ mAh$. How much energy is stored in it when fully charged (in $kJ$)?

$A$ constant voltage is applied between two ends of a metallic wire. If the length is halved and the radius of the wire is doubled,the rate of heat developed in the wire will be

The heat developed in an electric wire of resistance $R$ by a current $I$ for a time $t$ is

$A$ student in a town in India,where the price per unit $(1 \text{ unit} = 1 \,kWh)$ of electricity is $₹ 5.00$,purchases a $1 \,kVA$ $UPS$ (uninterrupted power supply) battery. $A$ day before the exam,$10$ friends arrive at the student's home with their laptops and all connect their laptops to the $UPS$. Assume that each laptop has a constant power requirement of $90 \,W$. Consider the following statements.
$I.$ All the $10$ laptops can be powered by the $UPS$,if connected directly.
$II.$ All the $10$ laptops can be powered,if connected using an extension box with a $3 \,A$ fuse.
$III.$ If all the $10$ friends use the laptop for $5 \,h$,then the cost of the consumed electricity is about $₹ 22.50$.
Select the correct option with the true statements.

If the current in an electric bulb is changed by $1\%$,then the percentage change in power will be ............. $\%$.

An electric heater of resistance $6 \, \Omega$ is run for $10 \, \text{minutes}$ on a $120 \, \text{V}$ line. The energy liberated in this period of time is: