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Question: If a 30 V, 90 W bulb is to be worked on a 120 V line, a resistance of how many ohms should be connec...

If a 30 V, 90 W bulb is to be worked on a 120 V line, a resistance of how many ohms should be connected in series with the bulb

A

10 ohm

B

20 ohm

C

30 ohm

D

40 ohm

Answer

30 ohm

Explanation

Solution

By using Series resistanceR =(Voperating−VRPR)×VR\text{Series resistance}R\ = \left( \frac{V_{operating} - V_{R}}{P_{R}} \right) \times V_{R}

(As we discussed in theory) ⇒ R=(120−30)90×30=30ΩR = \frac{(120 - 30)}{90} \times 30 = 30\Omega