A household circuit breaker is marked 220V,15A.Now an iron rated 220V,1100W and a cooker rated 220V,550W are connected in parallel to the main socket
How many light bulbs rated 220V,100W at most can still be connected in parallel to the mains without triggering the circuit breaker ?
physics circuit
2011-09-28 2:09 am
回答 (3)
2011-09-28 3:43 am
✔ 最佳答案
You could use the "power approach", which is much simpler without the need to calculate the resistance of individual appliances.The max power delivered by the hosehold mains
220 x 15 w = 3300 w
Power left for light bulbs
= (3300 - 1100 - 550) w = 1650 w
Since each light bulb consumes 100 w,
no. of light bulbs that can be connected = 1650/100 = 16.5
Therefore, only 16 light bulb can be connected.
2011-09-28 6:31 am
用p=iv計總功率為3300w，其他嘅係加減數，你應該識計。
2011-09-28 2:43 am
marked 220V,15A
=When current>15A, it breaks
Therefore, the maximum resistance
=220/15=14.67ohm
The resistance of the iron=220^2/1100=44ohm
The resistance of the cooker=220^2/550=88ohm
The resistance of each light bulb=220^2/100=484ohm
Let the number of the light bulbs be n
Equivalent resistance=
(44^-1+22^-1+n(484)^-1)^-1<(14.67)^-1
1/44+1/88+n/484<0.06818
n/484<0.03409
n<16.5
At most 16 light bulbs can still be connected to the mains
=When current>15A, it breaks
Therefore, the maximum resistance
=220/15=14.67ohm
The resistance of the iron=220^2/1100=44ohm
The resistance of the cooker=220^2/550=88ohm
The resistance of each light bulb=220^2/100=484ohm
Let the number of the light bulbs be n
Equivalent resistance=
(44^-1+22^-1+n(484)^-1)^-1<(14.67)^-1
1/44+1/88+n/484<0.06818
n/484<0.03409
n<16.5
At most 16 light bulbs can still be connected to the mains
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