把阻值为R的金属丝拉长，它的电阻值将______；把阻值为R的金属丝对折，它的电阻值将______．（均选填“变大”、“不变”或“变小”）
根据影响电阻大小因素可知，当材料、横截面积一定时，导体越长，电阻越大，当材料、长度一定时，导体横截面积越小，电阻越大．
当把金属丝拉长时，长度变长导致电阻变大，同时横截面积变小也导致电阻变大；
当把金属丝对折时，长度变短导致电阻变小，同时横截面积变小也导致电阻变小；
故答案为：变大；变小．
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| There was once a man named Goldsmith. He had a 1 heart. He was always 2 to help others and to share with them 3 that he had. He 4 so much to the poor 5 he was always poor himself. He was sometimes called Doctor Goldsmith, for he had studied medicine. One day a poor woman asked Doctor Goldsmith to go to see her husband, 6 was very ill and could not eat. Goldsmith found that the family was in great need of 7 . The man 8 work for a long time, but he was not ill. He was hungry because there was no food in the house. " 9 at my room this evening," said Goldsmith to the woman, "and I'll give you some medicine for your husband." In the evening the woman called. Goldsmith gave her 10 paper box that was very heavy. "Here is the medicine," he said, "Take it and it will 11 your husband a great deal of good. But don't open the box 12 you get home. You will find the directions inside the box." When the woman reached her home, she sat down by her husband's side, and they opened the box. It was 13 pieces of money. And on the top 14 the directions: "TO BE TAKEN WHEN NECESSARY." 15 this way Goldsmith had given them all the money that he had. | ||||
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