Question

A torch bulb is rated 2.5 V and 750 mA
Calculate its : (i) Power (ii) Resistance (iii) the energy consumed if the
bulb is lighted for 4 hrs.?

Answer 1

V=2.5 V

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I=750mA=750x10⁻³A

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power =?

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we know that 
Power =V*I           
  =2.5x750x10⁻³
=1.875W

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resistance :
V=IR
R=V/I=2.5/750x10⁻³=3.3 ohms

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Energy consumed if a bulb is lighted for 4 hours :

= > E=p*t=1.875x4=7.500Wh=27x 10³ joules

Answer 2

Given :
V=2.5V
Current=I=750mA=750/1000=0.75A
P=?
P=VxI
=2.5x0.75
=1.875W
By Ohm's law :
V=IR
R=V/I
=2.5/0.75
=3.33 ohms
Energy=?
Time=4hrs
E=pxt
P=1.875x4x3600=27000joules or 27kJ