What do you mean by the power rating of an electrical appliance? How will you use it to calculate 

a) the resistance of the appliance, and b) the safe limit of current in it, while in use?

$\text{Power Rating of an Electrical Appliance:}$

$\bullet$ Every electrical appliance has a power rating which tells how much electricity it needs to work. This is usually given in watts (W) or kilowatts (kW) (1000W = 1kW). 

$\bullet$ Power rating is also accompanied by the maximum working voltage, an appliance needs to work with its full capacity. 

$\text{Calculation of Resistance of an Electrical Appliance:}$

$\bullet$ The relationship between Power Rating, Working Voltage and Resistance of an electrical appliance is $P=\frac{V^2}{R}$. 

$\therefore$ $R=\frac{V^2}{P}$

$\text{Calculation of Safe Limit of Current:}$

As we know, $P=VI$,

$\therefore$ $I=\frac{P}{V}$

$\bullet$ This current is the safe limit of an electrical appliance, if it is operated across maximum operating voltage $V$.