get to know about potential difference, and energy. Imagine you stand in first floor. the height is say 20 ft with respect to ground. Imagine you have a big pot to collect water in ground. If you do not pour water, no water gets collected in the pot. The water collected in say 10 minutes, is equivalent of energy. If you pour water drop by drop, then there is some current ( equivalent of rate of water being poured out) and in 10 mins you get some (nonzero) energy. If the current is increased to say 10LPM (litre per minute), you get 100 litres of water in 10 mins, and you get high energy, because you increased the flow rate of water. Power is product of voltage and current. So if voltage is present you do not get any power. (like the 115 operated light being off. You have the voltage, but since switch is off, no current flows, no power and hence no energy= power*time). You switch on, and power is related to the power of lamp you have placed. Current also depends on that If resistance of bulb is 115 ohms [not cold resistance, be aware..], then current with V= 115V is 1 amp, and power is 115 watts. Keep it on for 1 hr and you have utilized 115watthour of energy. Keep it on for 8.7 hours and you have utilized 1 unit of energy = 1 kWhour.
You place a bulb with resistance of 57.5 ohms and current will be 2 amps when switch is ON, at 115V. Keep it on for 1 hour and you have utilized 230 watthour of energy. How long should you keep it On for utilizing 1 unit (= 1kWHr)? 4.35 hours.
So when switch is OFF, no current flows, and the voltage is just not useful. If current is zero, no work gets done. So energy utilised. Same with fans. when switch if OFF, voltage is still present (and is available) but not connected to fan. the fan does not run, and you do not get any cooling effect.
Power is ability to lift a weight, say. Work done is how long the weight has been lifted... If you lift a 20Kg weight, and remain carrying it for 30mins Hr, then work is done. If the time you lift the weight is 30 secs, the work done is lesser by a factor of 60. So learn to save energy, by turning off all gadgets when not in use. If we have no burglars, theoretically we can possibly save a lot of energy by turning off the street lights say after 10pm till 5 am. [God save the late comers..]
voltage is just pressure.. Current is type of energy required to drive circuit.
Well there is lots of blood in our veins, but is that enough to keep us alive? Nope.
The blood must keep moving.
Note that blood is analogous to voltage.
It's the same for electricity.
Your question is not understandable.
whether voltage only not enough in circuit
