2  4.0 Volts x 5.55 Amps = 66 Watts

 3  3.0 Volts x 6.25 Amps = 75 Watts

[1] Early work used term Intensity for electricity in wire.

2)_ You connect  two 6 volt 25 Watt bulbs in series across the battery. 

    2a_ Bulb: 6 Volts, 25 Watts = 1.44 OHMS = 4.166 AMPS (1.44 x 4.166 = 6) 

3)_ Measure the voltage across both bulbs: you will measure 6 volts across each. 
      (R = 2.88 OHMS, I = 4.166 AMPS) 

4)_ Now place another 6 volt 25 Watt bulb in parallel with either bulb--say the 
      bulb closest to ground. (R = 2.16 OHMS, I = 5.55 AMPS) 

5)_ Again measure the voltage across both bulbs: 

6)_ The single bulb (top) will measure   8    volts.  (1.44 OHMS) 

7)_ The two bulbs (bottom) will measure   4    volts.   (0.72 OHMS) 

8)_ Of course both voltages will equal   12    volts. 
 

DISCUSSION: 
If we think of the bulbs as resistors (they are within reason), notice that there is 6 volts dropped across one bulb in the first example. 

In the second example, when the second bulb is added, more current is made to flow, and the voltage across the single bulb went from 6 volts to 8 volts. 

In both cases the single bulb (resistor) is CONVERTING the CURRENT to a VOLTAGE: The more current the more voltage.

    Example #1: 4.166 AMPS across 1.44 OHMS = 6 Volts 

    Example #2: 5.55 AMPS across 1.44 OHMS = 8 Volts 
 

So changing the total resistance across the 12 Volt battery has converted a fixed VOLTAGE to a changingCURRENT.

SEE: Intuitive  Electronics Page