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Physics

A student wants to design a device to connect a bulb rated 10 W, 22 V, to the mains 220 V, so that the bulb operates at its rated voltage.

(a) Name the device he uses.

(b) State the principle involved in the working of this device.

(c) When the bulb is connected to the output of the device, calculate:

  1. Current drawn
  2. Resistance of the bulb

Current Electricity

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Answer

(a) Step-down transformer.

(b) Electromagnetic induction, according to this principle a changing current in the primary coil induces a voltage in the secondary coil of a transformer based on the turns ratio.

(c) Given,

  • Power of the bulb (P) = 10 W
  • Voltage of the bulb (V) = 22 V
  1. Current drawn = PV=1022\dfrac{\text P}{\text V} = \dfrac{10}{22} = 0.45 A
  2. Resistance of the bulb = V2P=22210=48410\dfrac{\text V^2}{\text P} = \dfrac{22^2}{10} = \dfrac{484}{10} = 48.4 Ω

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