a transformer has a primany voltage of 115 v and secondary voltage of 24 v if the number of tures in the primany is 345 how many turns are in the secondary

The voltage ratio
Vsecondary/Vprimary = 24/115 = 0.209
This equals the turns ratio
Nsecondary/Nprimary = Nsecondary/345 = 0.209

Therefore Nsecondary = 72

a man wants to illuminate 5 houses on his model railroad by wiring 5 20 ohm lamps in series.how much resistance must be added in the series in order to limit the current to the .5A needed by each light?

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To calculate the resistance required to limit the current to 0.5A for each lamp, we can use Ohm's Law.

The formula for Ohm's Law is:
V = I * R

where V is the voltage, I is the current, and R is the resistance.

In this case, we want to limit the current to 0.5A for each light, so I = 0.5A.

The total resistance in the circuit is the sum of the resistances of each lamp and the additional resistance we need to add.

Since we have 5 lamps, each with a resistance of 20 ohms, the total resistance of the lamps is 5 * 20 = 100 ohms.

To calculate the additional resistance needed, we can subtract the resistance of the lamps from the total resistance required:
R_additional = Total resistance - Resistance of lamps
R_additional = R_total - (R_lamp1 + R_lamp2 + R_lamp3 + R_lamp4 + R_lamp5)
R_additional = R_total - (5 * R_lamp)

Now we can substitute the values into the equation and solve for R_additional:

R_additional = R_total - (5 * R_lamp)
R_additional = R_total - (5 * 20)

Given that the desired current I is 0.5A, we can use Ohm's Law to find the desired voltage V: