12 a dc motor operating at no load has its highest...

12) A DC motor operating at no-load has it's highest efficiency. A) True B) False 12) 13) 13) When specifying a motor, one should always spec at a minimum 2x the power rating required to drive the load. A) True B) False 14) 14) Temperature rise is calculated by adding the temperature of the warmest part of the machine to the ambient temperature OR 40°C which ever is greatest. A) True B) False

Transcript

00:01 Okay, so let here in the first one the option is a and in the second one the option is c and the third one the option is b.

00:26 Okay and in the fourth one the option is also b in the fifth one the option is a and sixth one the option is a and in the seven the option is d in eight the option is a okay so let me clear out this here okay so if you are not compatible with this so i can show you here okay so in nine let this is the circuit okay and this is that motor and this is 240 volts okay so starting at 0 v sub a is i a r a and i sub a is v a is v a divided by r a which is 240 divided by 1 .5 so this is 160 ampers also at the pure load condition i sub a is 40 amps and later this is the so this is this is the stalling t sterling and the t pull load okay pull load so this is equal to k sub l times i sub a divided by kp i sub a which is i sub r divided by i sub up okay so the starting torque starting divided by t pull load pull load this is equal to 160 divided by poor t which is poor okay so the option is c now in part 10 here in part 10 here if we look at here so for a consistent torque load and the changing the armature resistance we are not change is made in the current so where the external resistance is added so the speed of motor decreases okay so this will be equal to e which is v minus i a r a this is 230 minus 05 times point and 6 0 okay so e sub 1 is 215 is 215 okay so when the resistance of 1 oom is added in the armature circuit the new half emf voltage will be e sub b2 which is v minus ia so this is 230 minus 1 .25 times 60 this is 15155 volts okay and e sub b1 e sub b2 divided by e b1 is equal to n2 divided by n1 and n2 divided by n1 is equal to 150 divided by 250 divided by 215 so this is point 7 2 and the answer is option d okay answer is option d now let me explain the 11th one okay so in 11 eb1 is equal to v minus i a 1 r a and i a 1 is i a 1 is i a 1 is it so this is 68 minus 2 .2 okay and i is i is equal to 65 .8 amps...

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