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X Abdulrahman X:
Physics>May/June 08>P3(First Variant Question Paper)
Question 8, (c)
The three 60W lamps are replaced by 3 energy-saving ones, that give the same light output buy are rated at only 15W each.
Calc,
(i) The total reduction in power...
(ii) the energy saved when the lamps are lit for 1hr...
Could someone explain this with the working out pls, only the answers are written in the mark scheme. Thank You
emi:
c) i - total reduction in power:
first calculate both the powers before and after
P1 before replacing: 60x3= 180w
P2 after replacing: 15x3= 45w
subtract ____________
135 w is the reduction in power
ii) energy saved when lights are lit for one hour
calculate the energy while using 3 ,60w lamps = VIT = 60x3x3600 = 64000
calculate the engery while using 3, 15w lamps = VIT = 15x3x3600 =162000
subtract __________
486000 J energy saved 468 KJ
X Abdulrahman X:
Thank You emi ur seriously amazing ;D
looks like u will do well in ur physics :P
emi:
inshallah :)
emi:
plz help me with this Question : its from my text book ..
Q- a 3kW electric heater is used to heat up 2.5kg of water of specific latent heat capacity 4200J/kg/c . the initial temp is 16 degree. Work out the final temp. after the heater has been switched on for 2 minutes ?
wats the way to solve this ??? plz someone
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