Which of the following is true for electrical energy?

When we pay for our electricity bill, we are paying for the:

An electric kettle is rated as $2.5\ kW, \ 250\ V$. Find the cost running the kettle for two hours at $60\ \text{paisa}/\text{unit}$.

An electric bulb rated for $500$W at $100$ V is used in a circuit having a $200$V supply. The resistance R that one must put in series with the bulb, so that the power delivered in the bulb is $500$W is ______$\Omega$.

Four bulbs, each of rating (100 W, 220 V) and connected in parallel across a voltage supply of 220 V, are operated for five hours daily. If all the bulbs are replaced by LEDs of rating (8 W, 220 V), how many units of electrical energy will be saved every month (30 days)? 

How much energy in kilowatt hour is consumed in operating ten 50 watt bulbs for 10 hours per day in a month (30 days)

A geyser of $2.5 kw$ is used for $8$ hours daily. Calculate the monthly consumption ( 30 days) of electrical energy units. Also calculate the cost of electricity units consumed in a month if rate per unit is $3.50$

If voltage across a bulb rated $220V-100W$ drops by $2.5$% of its rated value, the percentage of the rated value by which the power would decrease is

A padcular ohmmeter uses a battery to provide a potential difference across an unknown resistance  whose value S to be measured. The meter measures the resulting current through this resistor and is calibrated to read out corresponding value of resistance. Suppose that this ohmmeter is used to measure he resistance of a typical incandescent tungsten-filament light bulb. The value of the resistance of the light bulb will be

A $500\ W$ heating unit is designed to operate on a $115\ V$ line. If line voltage drops to $110\ V$ line, the percentage drop in heat output will be: