How do i find the potential difference across and what formula should i use to find the power?

This is a series circuit.
If you are an electron coming out of one terminal of the generator,
you have to flow through

                       ==> one side of the cable,
                       ==> the lights,
                       ==> the other side of the cable

in order to get back to the other terminal of the generator.

Each side of the cable is a resistor, with resistance of 1 ohm.
The voltage across a resistor is (current) x (resistance).
So the voltage between the ends of one side of the cable is

            (10 A) x (1 ohm)  =  10 volts .

The current LOSES ENERGY from pushing through the resistors (cable).
It loses 10 volts pushing through each side of the cable.
So, out at the end where the floodlights are, there's only
(240 - 10 - 10) = 220 volts across the lights.


Every electron that leaves the generator has to flow around the
whole loop and return to the generator.  New electrons can't be
born anywhere, and they can't disappear.

So the current is the same at every point in a series circuit.
In this circuit, it's 10 A.

Electrical power is  (voltage) x (current) .

In the floodlights, that's   (220 V) x (10 A)  =  2,200 watts.


Notice that there's a voltage across each side of the cable too ... 10 volts.
So there's power there too.

On each side of the cable, power = (10 V) x (10 A) = 100 watts !

100 watts of power gets lost pushing the electrons through the cable.
On both sides of the cable, that's 200 watts of lost power.
Where does it go ? ?

The cable gets warm, and it heats up the air around it.

THIS is why it's dangerous to plug too many things all into the
same extension cord in your house.  The extension cord has
some resistance, so some power is used to push the current
through it.  If you plug too many things into it, the current will
get too big.  The cord will get hot, and that could burn the dog
or even start a fire.

Efficiency is an act of doing something

The low lands i believe