question on calculating transformer questions (1 Viewer)

[angmor]

ok for my prac exam, we have to build a transformer using two primary and secondary coils provided, and then determine the ratio of the primary and secondary coils.

our power source is connected to the primary coil, and there is going to be a resistor put in place. Our secondary coil will be connected to a galvanometer, most likely.

my question is, how do we work out the ratio when we know the primary input voltage, and the secondary output current? is it possible and is it right to convert the primary voltage into current by using V=IR?

 

[alcalder]

Where is the resistor? Primary or secondary circuit?

If the known resistor is in the secondary circuit, then certainly

V_secondary = I_secondaryR

In an ideal transformer, there should be no power loss, so: (p=primary, s=secondary)

P_p=P_s

V_pI_p=V_sI_s

BUT IN A TRANFORMER
V_p/V_s = n_p/n_s

SO
I_s/I_p = n_p/n_s

In that case, if the resistor is in the primary circuit.

V_p =I_pR

Find the primary input current, you know the secondary output current and can hence find your ratio.