李明组装了一直流电动机模型,闭合开关后,发现线圈不转,请分析原因可能有几种。
答:线圈开始时在平衡位置;磁铁的磁性太弱或供电电流太小;电路接触不良;摩擦力太大。
用所给词的适当形式填空。
1. My family _______ (decorate) our house before Christmas every year.
2. We _______ (celebrate) Christmas with a family meal.
3. I _______ (send) some Christmas E-card to my friends last year and I _______ (be) really happy
to _______ (make) a contribution to the environment protection.
4. People always _______ (sing) Traditional Christmas songs at Christmas.
5. My mother with my little sister usually _______ (go) shopping before Christmas.
6. My classmate, Xiao Ming, never _______ (go) to the parks on weekends. She just _______ (do)
homework. She _______ (study) hard. But I ______ (not agree) with her. I _______ (think) she’d
better _______(have) a rest after hard work.
7.Mike ______ (not feel) well. He ______ (feel) sick, and his parents ______ (look) worried.
使用油气混烧的加热炉,不需要使用吹灰器对炉膛进行定期吹扫。