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A physics question about electricity, 10 marks
發問:
An electric heater takes a time (T) to boil a kettle of water when connected to a 200 V source. What will be the time required to boil the same kettle of water when the heater is connected to a 100 V source ? (assume that the resistance of the heater remains unchanged). The answer is 4T. How to calculate?? thx
最佳解答:
An electric heater takes a time (T) to boil a kettle of water when connected to a 200 V source. What will be the time required to boil the same kettle of water when the heater is connected to a 100 V source ? (assume that the resistance of the heater remains unchanged). 電功率 P = V2/R 所以當電壓由200V變為100V時它的功率變為 Po = V2/R = 2002/R = 40000 / R 新功率為 P = V2/R = 1002/R = 10000 / R = Po / 4 兩者發出相等的能量來煲水，則 Po T = P T’ Po T = (Po/4) T’ T’ = 4T
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