30.When the resistance of an electric heater is reduced by half, which of the following statements is/are correct?
(1)The voltage across the heater is reduced by half.
(2)The power dissipated by the heater is doubled.
(3)The current through the wire is doubled.
A.(1) only
B.(3) only
C.(1) and (2) only
D.(2) and (3) only
E.(1), (2) and (3)
電學問題!!!!!!!!!!!!!!1
2007-04-03 9:03 pm
回答 (3)
2007-04-04 6:07 am
✔ 最佳答案
答案為D.1) 只改變電阻,電源未變故電壓不變.(1)錯
2) P=V^2/R, V不變, R減半 故 P變為 2倍 (2) 對
3) I=V/R, V不變, R減半 故I 變為2倍 (3)對
2007-04-04 4:46 am
it should be B
I=E/R
I=E/R
2007-04-03 11:00 pm
(1) Based on V=IR , V=voltage ,I=current ,R=resistance
If the resistance of an electric heater is reduced by half, the current should not be changed ,and the voltage must be reduced by half , so (1) is correct.
(2)If the resistance is reduced by half , the dissipation of power must be reduced and not increased , so (2) is wrong.
(3)the current will not be changed , because only the resistance of an electric heater is reduced , not the resistance of electric cell reduced .
Therefore I think the answer is A (1) only
I hope I am right
If the resistance of an electric heater is reduced by half, the current should not be changed ,and the voltage must be reduced by half , so (1) is correct.
(2)If the resistance is reduced by half , the dissipation of power must be reduced and not increased , so (2) is wrong.
(3)the current will not be changed , because only the resistance of an electric heater is reduced , not the resistance of electric cell reduced .
Therefore I think the answer is A (1) only
I hope I am right
參考: my physical knowledge
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