A bulb is rated 40 watt 220 volt find the current drawn by eat when it is connected to a 220 volt supply also find its resistance if the given blood bulb is replaced by a bulb operating 25 Watt 220 volt will there be any change in the value of current and resistance justify your answer and determine the change
Answers
case 1 : power of bulb , P = 40 watt
voltage supplied across the bulb , V = 220V
we know, power supplied by bulb , P = Vi
or, 40 = 220 × i
or, i = 40/220 = 2/11 = 0.18 Amp
again, use formula, P = V²/R to find resistance of bulb
or, P = V²/R
or, R = V²/P
or, R = (220)²/40 = 48400/40 = 1210 ohm
case 2 : if given bulb is replaced by a bulb operating 25 watt , 220 volt.
so, current, I = P'/V = 25/220 = 0.1136 Amp
resistance, R' = V²/P' = (220)²/25 = 1936 ohm.
here it is clearly shown that when we change bulb , current and resistance will be change.
change in current = 0.18 - 0.1136
= 0.0664 Amp [ current decreases when we use 25 watt bulb in place of 40 watt bulb ]
change in resistance = 1936 - 1210= 726 ohm [ resistance increase when we use 25 watt bulb in place of 40 watt ]
Answer and Explanation:
Case I: Bulb rated as 40 watt 220 volt
Power of bulb, P = 40 watt = 40 W
Potential difference, V = 220 volt = 220 V
As we know, Power = Potential difference × Current
Let the current be I.
Now,
P = V×I
I = P/V
I = 40/220
I = 0.182 ampere = 0.182 A
For finding the resistance of the bulb, we have another formula of power as
P = V²/R
R = V²/P
R = (220)²/40
R = 48400/40
R = 1210 Ω
Case II: Bulb rated as 25 watt 220 volt
Power of bulb, P = 25 watt = 25 W
Potential difference, V = 220 volt = 220 V
As we know, Power = Potential difference × Current
Let the current be I.
Now,
P = V×I
I = P/V
I = 25/220
I = 0.114 ampere = 0.114 A
For finding the resistance of the bulb, we have another formula of power as
P = V²/R
R = V²/P
R = (220)²/25
R = 48400/25
R = 1936 Ω
Difference in current = 0.182 - 0.114 = 0.068 A [Current decreases]
Difference in resistance = 1936 - 1210 = 726 Ω [Resistance increases]
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