HELP!

[jonnymc11]

I dont no how to do the following question...

A single-phase circuit dissipates 2.5 kW of power and operates at a power factor of 0.95. The current flowing in the circuit will be:

a) 11.4 A B) 10.32 A c) 10.8 A d) 10.4 A

ALSO IS THIS CORRECT, i have tried it myself?

The voltage supplied to the primary winding of an ideal step down transformer is 1000V and the output voltage is 400V. If the secondary current is 20A the value of the primary current will be:

a) 50 A B) 25 A c) 10 A d) 8 A

1000/400 = 2.5

20/2.5 = 8

These are part of the 301 exam, which i am flapping about. One lad in the class done his last night, he's had "distinctions" throughout the 3 years and found this one "hard" and got a "PASS"...

so im ray

 

[Mikeymike]

I dont no how to do the following question...A single-phase circuit dissipates 2.5 kW of power and operates at a power factor of 0.95. The current flowing in the circuit will be:

a) 11.4 A B) 10.32 A c) 10.8 A d) 10.4 A

Single phase means its = 230v supply

Formula: V x P.F - 230v x 0.95 = 218.5v

KW/V = I - 2500/218.5 = 11.4A

ALSO IS THIS CORRECT, i have tried it myself?

The voltage supplied to the primary winding of an ideal step down transformer is 1000V and the output voltage is 400V. If the secondary current is 20A the value of the primary current will be:

a) 50 A B) 25 A c) 10 A d) 8 A

1000/400 = 2.5

20/2.5 = 8 thats what Id go for.

My way would be

vp np Is - 1000v - 20A 400 x 20 Divide by 1000 = 8A

vs ns Ip - 400v -

These are part of the 301 exam, which i am flapping about. One lad in the class done his last night, he's had "distinctions" throughout the 3 years and found this one "hard" and got a "PASS"...

so im ray

Hope this helps alittle m8