a high intensity desk lamb is rated at 45W but requires only 12V. It contains a transformer: details below?

Question

the transformer converts 120-V, household voltage, the step-down transformer. what is the current in the secondary coil when the lamb is on? what is the currnet in the primary coil? what is the resistance of the bulb when on?
please help!!

Answer 1

If you assume the Transistor is ideal, then there is no loss in the transformer and all the power applied on the primary side is delivered to the secondary. The voltage at the secondary is 12V rms AC. You can find the turns ratio of the transformer because you know the primary and secondary voltages. (a = 120/12 = 10). You can find the secondary current by dividing the lamp power by the voltage across it. (I2 = 45W/12V = 3.75 A rms). The lamp resistance in the steady state on condition, is the secondary voltage divided by the secondary current. ( R = 12 / 3.75 = 3.2 Ohm) Because power is conserved for the ideal transformer (V1*I1 = V2*I2), you can solve this for the primary current (I1). Or, because you already know the turns ratio, you can just divide the secondary current by the turns ratio to find the primary current. (I1 = I2/a = 3.75/10 = 375 mA rms)

Hope this helps.

Answer 2

The formulas you'll need are E=IR and P=IE
where E=voltage, I=current, R=resistance and P=power.

The 45W lamp at 12 volts draws:
45=12*I
I=45/12 or 3.75 amps and this represents the current in the transformer secondary.

For the primary, we have 45=120*I
I=45/120 or 0.375 A or 375 mA.

The bulbs resistance is R=12/3.75 or 3.2 Ohms.

Answer 3

High Intensity Desk Lamp