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[Banjo]

Hi

Just wondering if somebody could help me out with some questions I'm struggling with and show your workings out to

Q1) A transformer has an output of 12KVA and a power factor of 0.9, the total losses in the transformer are 600w, what is the efficiency of the transformer?

A) 96.4%

B) 92.4%

C) 94.4%

D) 94.6%

Q2) If a current of 200ma flows into a capacitor for 40ms, how much charge will develop in the capacitor?

A) 0.8mc

B)16mc

C)8mc

D)18mc

Q3) Calculate the induced EMF in a conductor with a length of 0.65m moving at right angles at a velocity of 2m/s through a magnetic field that has a flux density of 0.9 Tesla?

A) 1.17v

B) 2.34v

C) 23.4v

D) 11.7v

Cheers Stu

 

[msb2003]

Try this,

Q1. If the load has a power factor of 0.9 then the true power is appartent power, KVA x p.f, so 12000 x 0.9 = 10800W

efficiency = output / (output+losses) x 100%, so 10800 / (10800 + 600) = 0.947 x 100% = 94.7%

Q2. The charge stored in a capacitor is Q=IT , so Q = 200exp-3 x 40 exp-3 = 0.008 = 8mC

Q3. Indused e.m.f. = magnetic field density x effective length of conductor x velocity , so e=Blv, e= 0.9 x 0.65 x 2 = 1.17v

hope this helps

regards

Mark