Halogen bulbs have some differences from standard incandescent lightbulbs. They

Question

Halogen bulbs have some differences from standard incandescent lightbulbs. They are generally smaller, the filament runs at a higher temperature, and they have a quartz (rather than glass) envelope. They may also operate at lower voltage. Consider a 12 V, 50 W halogen bulb for use in a desk lamp. The lamp plugs into a 120 V, 60 Hz outlet, and it has a transformer in its base.

Part A) The 12 V rating of the bulb refers to the rms voltage. What is the peak voltage across the bulb?

A. 17V B. 12V C. 8.5V D. 24V

Part B) Suppose the transformer in the base of the lamp has 500 turns of wire on its primary coil. How many turns are on the secondary coil?

A. 50 B. 500 C. 5000 D. 160

Part C) How much current is drawn by the lamp at the outlet? That is, what is the rms current in the primary?

A. .42A B. 1.3A C. 4.2A D. 13A

Part D) What will be the voltage across the bulb if the lamp's power cord is accidentally plugged into a 240 V, 60 Hz outlet?

A. 48V B. 2V C. 36V D. 24V

Explanation / Answer

A) A) 17 V

Vpeak = sqrt(2)*Vrms

= 1.414*12

= 17 volts

B) A) 50

N1/N2 = V1/V2

==> N2 = (V2/V1*N1

= (12/120)*500

= 50

C) A) 0.42 A

P_primary = Irms*Vrms

==> Irms = P_primary/Vrms

= 50/120

= 0.42 A

D) D) 24 V

N1/N2 = V1/V2

==> V2 = V1*(N2/N1)

= 240*(50/500)

= 24 v

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