A #10 copper conductor with an insulation rating of 90 degrees C is rated at 30 amps. A 40 amp circuit would need a #8 wire. To do a voltage drop calculation for a distance of 65 feet, a voltage of the circuit must be stated. Depending on the answer obtained from the calculation you might have to jump up one more size to #6.
8 ga
In residential wiring applications the most used is 14 gauge wire for light switches as long as the circuit breaker or the fuse is 15A. If your lighting circuit is on a 20A fuse/circuit breaker then you need to use 12 gauge wire
yes
15 amps
yesAnother (corrected) answer.NO! The circuit breaker is there to protect the wiring from overheating. It wouldn't matter where on the circuit you decided to put the 14 gauge wire, you would need to change the breaker to 15 Amp if you did that. Using 14 gauge wire on a 20 amp circuit is a fire hazard and contrary to UBC. Contact your local building and zoning department to verify.
12 gauge underground wire or if you think you will ever add any devices to this circuit use 10 gauge.
8 ga
In residential wiring applications the most used is 14 gauge wire for light switches as long as the circuit breaker or the fuse is 15A. If your lighting circuit is on a 20A fuse/circuit breaker then you need to use 12 gauge wire
10 gauge
AWG #6 wire.
#6 wire is good for 65 Amps as long as it is type THHN.
Use AWG # 6 wire.
Use 8 gauge wire.
No, you can never mix wire sizes in a circuit.
14 AWG.
yes
15 amps