2) Does using a 10 feet long power extension cord results in more consumption of electricity compared to a direct plug point from the wall ?
3) Would I waste electricity if I only use 2 of the plug points in a 5 plug points extension cord (10 feet long) ?
4) Does "energy saving" devices work. What do they do/how do they work and where should such devices be installed ?
1) by "bigger" do you mean longer, or thicker? If it is longer, then the power consumption goes up. If it is thicker, the power consumption goes down.
2) yes. *ANY* added resistance (longer cable) adds to the power loss. An extra 10 feet of extension cord might only add a negligible extra power loss, but it is there.
3) No. Any unused plugs do not draw more power.
4) Yes. Under most circumstances. Electronic devices that have standby modes use power all-the-time. If they are ‘energy saving’ then that standby power is reduced to a very small amount.
Computer monitors, laptops, cell phones, iPods, etc that go into a sleep mode are energy saving.
Devices with electric motors (refrigerator, fans, washing machine/dryer, etc) can have a device installed that reduces the power drawn by the motor with only a minimal loss of mechanical torque.