Question

[ It is marked as 40W 230V on an incandescent lamp. If it is given 115V to this lamp, its power

will be ...... ]

40W
20W
10W
none of above​

Answer 1

Answer:

10W

Explanation:

There are two ways you can solve this                                                                                                                                  1-First we find the resistance of the bulb using P=V²/R   as P and V are given in the rating it becomes  40=(230)²/R      R=1322.5 ohms .Now we know the resistance which remains same so we can calculate the second power using the same relation P=(115)²/1322.5       P=10W                                                        2-This is a much simpler method take ratio     P₁/P₂=V₁²/V₂²  ⇒  40/P₂=230²/115²              P₂=40/4=10W

Answer 2

Power of bulb will be 10W  if 40W 230V  is given 115V

Explanation:

Power of the bulb = V²/R

Power = 40W

Voltage = 230V

40  = 230²/R

=> R = 230²/40

R - Resistance of the bulb

now when voltage is 115 V

P = 115²/R

P =  115²/(230²/40)

=> P = 40 ( 115/230)²

=> P = 40 (1/2)²

=> P = 40/4

=> P = 10 W

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