Heater係用高resistance定係低resistance

決定 heater 的 resistance ，要考慮兩個因素：
powerefficiency在理想的情況下，根據 P = V²/R，Heater 的 resistance 越少，power 越大，越能夠迅速加熱，所以 heater 的 resistance 會比其他家電低。

但是，實際上，resistance 並非越低越好，因為電路中的電線、電源及heater電路中的其他部份都會有 restistance (R2)，如果 heater 的 resistance (R1) 太低，R1 的 p.d. 會變少，R2 的 p.d. 會變得大，很多電力會浪費在 R2 ，甚至可能令 R2 過熱，所以 heater 的 resistance 要低，但比整個電路的其它電阻高。

一般學生都錯誤以為 heater 的 resistance 要高，因為他們知道電流流過電阻會生熱，便以為電阻越大，產生的熱量會越大。無錯，電流流過電阻會生熱，但是若電阻增加，電流會減少 (因為 V = IR)，所釋放出來的熱能也會減少 (P = I² R)。

It should be low resistance.
The heating effect of a heater is due to the current that flows through the heating element. A lower resistance permits a higher current to pass through, thus producing more heat.
Examples, a 1000W heater connected to the domestic mains of 220 V would have a resistance of,
using power = voltage^2/resistance
or resistance = voltage^2 /power = 220^2/1000 Ohms = 48 Ohms
A 500W heater will have a resistance of
resistance = 220^2/500 Ohms = 97 Ohms
Hence, a higher power heater should have a lower resistance.

Of course high resistance.
Heat is given out when electrons pass through a high resistance area.
As heater is use to give out heat, an ideal heater should have high resistance.