# 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?

why does tv's, computers, steros, get so dusty

## 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)

R_additional = R_total - 100

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

V = I * R_additional

V = 0.5A * R_additional

Since the voltage across the lamps in series is the same, the voltage across each lamp is the desired voltage V.

Now you can substitute the known values and solve for R_additional:

V = 0.5A * R_additional

V = 0.5A * (R_total - 100)

Finally, you'll need to measure the voltage across the lamps and calculate the value of R_additional using the equation above.

As for why TVs, computers, and stereos get dusty, it is because of their design and the environment they are in. Dust particles are naturally present in the air, and these particles can settle on the surfaces of electronic devices over time. The fans and ventilation systems in these devices may also draw in air, which can bring in more particles. Additionally, static electricity can attract dust and cause it to cling to surfaces. Regular cleaning and proper ventilation can help reduce the accumulation of dust on these devices.