【導讀】帶電粒子在電場、磁場中的運動是高中物理中的重點內(nèi)容，這類問。題對學生的空間想象能力、分析綜合能力、應用數(shù)學知識處理物理問題的能力有較高的要求，是考查考生。多項能力的極好載體，因此成為高考的熱點，在實行了多年的理科綜合能力測試中也是每年都考，且分值。題．考題有可能以科學技術的具體問題為背景，從實際問題中獲取并處理信息，把實際問題轉(zhuǎn)化成物理問。題，提高分析解決實際問題的能力是教學中的重點．計算題還常常成為試卷的壓軸題，如2020年全國理。綜卷Ⅰ第26題、全國理綜卷Ⅱ第25題、重慶理綜卷第25題、四川理綜卷第25題；2020年全國理綜卷Ⅰ。在2020年高考中仍然會出現(xiàn)帶電粒子在復合的或組合的電場和磁場中運動的問題．。對于帶電粒子在電場中的加速問題，應突出動能定理的應用．。電荷量為q、質(zhì)量為m的帶電粒子由靜止開始經(jīng)電壓U1加速后，以速度v1垂直進入由兩帶電平行金。體沒有特殊交代時，應當考慮其重力；③對未知名的、

　　

【正文】 標平面向內(nèi)的有界圓形勻強磁場區(qū)域 (圖中未畫出 )；在第二象限內(nèi)存在沿 x 軸負方向的勻強電場．一粒子源固定在 x 軸上的 A 點， A 點坐標為 (－ L,0)．粒子源沿 y 軸正方向釋放出速度大小為 v 的電子，電子恰好能通過 y 軸上的 C 點， C 點坐標為 (0,2L)，電子經(jīng)過磁場偏轉(zhuǎn)后恰好垂直通過第一象限內(nèi)與 x 軸正方向成 15176。角的射線 ON(已知電子的質(zhì)量為 m，電荷量為 e，不考慮粒子的重力和粒子之間的相互作用 )．求： 23 甲 (1)第二象限內(nèi)電場強度 E 的大?。? (2)電子離開電場時的速度方向與 y 軸正方向的夾角 θ． (3)圓形磁場的最小半徑 Rm． 【解析】 (1)從 A 到 C 的過程中，電子做類平拋運動，有： L＝ eE2mt2 (1 分 ) 2L＝ vt (1 分 ) 聯(lián)立解得： E＝ mv22eL． (1 分 ) (2)設電子到達 C 點的速度大小為 vC，方向與 y 軸正方向的夾角為 θ．由動能定理，有： 12mvC2－ 12mv2＝ eEL (2 分 ) 乙 解得： vC＝ 2v cos θ＝ vvC＝ 22 (1 分 ) 解得： θ＝ 45176。． (1 分 ) (3)電子的運動軌跡圖如圖乙所示，電子在磁場中做勻速圓周運動 的半徑 r＝ mvCeB ＝ 2mveB (1 分 ) 電子在磁場中偏轉(zhuǎn) 120176。后垂直于 ON 射出，則磁場最小半徑為： Rm＝ PQ2 ＝ rsin 60176。 (2 分 ) 由以上兩式可得： Rm＝ 6mv2eB ． (1 分 ) [答案 ] (1)mv22eL (2)45176。 (3)6mv2eB 16． (13 分 )如圖甲所示，豎直擋板 MN 的左側(cè)空間有方向豎直向上的勻強電場和垂直紙面向里的水平勻強 磁場，電場和磁場的范圍足夠大，電場強度的大小 E＝ 40 N/C，磁感應強度的大小 B 隨時間 t 變化的關系圖象如圖乙所示，選定磁場垂直紙面向里為正方向．在 t＝ 0 時刻，一質(zhì)量 m＝ 8 10－ 4 kg、帶電荷量q＝＋ 2 10－ 4 C 的微粒在 O 點具有豎直向下的速度 v＝ m/s， O′ 是擋板 MN 上一點，直線 OO′ 與擋板 MN 垂直，取 g＝ 10 m/s2．求： 24 (1)微粒下一次經(jīng)過直線 OO′ 時到 O 點的距離． (2)微粒在運動過程中離開直線 OO′ 的最大距離． (3)水平移動擋板，使微粒能垂直射到擋板上，擋板與 O 點間的距離應滿足的條件． 【解析】 (1)由題意知，微粒所受重力 G＝ mg＝ 8 10－ 3 N 電場力大小 F＝ Eq＝ 8 10－ 3 N (1 分 ) 因此重力與電場力平衡 微粒先在洛倫茲力的作用下做勻速圓周運動，則有： qvB＝ mv2R (1 分 ) 解得： R＝ mvqB＝ m 由 T＝ 2πRv (1 分 ) 解得： T＝ 10π s (1 分 ) 則微粒在 5π s 內(nèi)轉(zhuǎn)過半個圓周，再次經(jīng)直線 OO′ 時與 O 點的距離 l＝ 2R＝ m． (1 分 ) (2)微粒運動半周后向上勻速運動，運動的時間 t＝ 5π s，軌跡如圖丙所示． 丙 位移大小 x＝ vt＝ m＝ m (2 分 ) 微粒離開直線 OO′ 的最大距離 h＝ x＋ R＝ m． (2 分 ) (3)若微粒能垂直射到擋板上的某點 P， P 點在直線 OO′ 下方時，擋板 MN與 O 點間的距離應滿足： L＝ (4n＋ 1) m (n＝ 0,1,2? ) (2 分 ) 若微粒能垂直射到擋板上的某點 P， P 點在直線 OO′ 上 方時，擋板 MN 與 O點間的距離應滿足： L＝ (4n＋ 3) m (n＝ 0,1,2? )． (2 分 ) [若兩式合寫成 L＝ (＋ ) m (n＝ 0,1,2? )同樣給分 ] [答案 ] (1) m (2) m (3)P 點在直線 OO′ 下方時，距離 L＝ (4n＋ 1) m (n＝ 0,1,2? ) P 點在直線 OO′ 上方時，距離 L＝ (4n＋ 3) m (n＝ 0,1,2? ) 25 [或 L＝ (＋ ) m (n＝ 0,1,2? )] 26 （英文版 ） easily blame, to prevent the broken window effect. Supervise the leading cadres to play an exemplary role, take the lead in the strict implementation of the code and rule , lead to safeguard the solemnity and authority of the party discipline, ensure that the party discipline and the laws and regulations for implementation in place. Throughout the discipline in the daily supervision and management , strengthen supervision and inspection, from the thorough investigation of violations of discipline behavior. Strengthen to key areas, key departments and key projects as well as the masses reflect the concentration of the units and departments for supervision. strengthening supervision, discipline inspection and supervision of cadres to set an example for pliance with the code and rule is a man must be hexyl, blacksmith needs its own hardware. Discipline inspection ans as the executor of the party discipline, and supervisor of the defenders, for its supervision must be more strictly, discipline inspection and supervision of cadres to firmly establish the awareness of Party Constitution, sense of discipline and rules consciousness, politics loyalty, sense obey. Action speak Ji Ordinance to set an example of the 27 regulations of the rule of law, strengthen supervision and accept the supervision of the firmness and consciousness, do ply with and . To firmly establish the discipline must first be disciplined, the supervisor will be subject to the supervision of concept, and consciously safeguard and implement party passes party, take the lead in practicing three strict real strict, so loyal, clean, play. To be good at learning, the Constitution and the code as morality, politics and brought to fruition。 to implement , do not want to, dare not, not with disciplinary ruler to supervision。 to discipline a ruler, often the control inspection, and consciously in the ideological red line to draw the row Ming Good accumulation is indeed the bottom line, so that the heart has fear, said to have quit, the line has ended. Attached: indifferent to heart, calmly to the table in our life, there are many unpredictable things will happen, some good, some bad things, we cannot control is powerless to stop, but with time, you will find in life sometimes turns out to be not good, some bad things finally turned out to be a good thing, but then we muddy however did not know, this is the life teach us things. 1, life can be plex, can also be simple. Want simple life of precipitation, to have enough time to reflect, to make Bee 28 more perfect. Life is the most important thing is not to win, but the struggle。 not to have conquered, but to have fought well. 2, the plain is the background of life. Live a plain life, give up on themselves is not a coward, but the wise answers。 not disillusioned after the heart, such as ashes, but experience the storm after the enlightenment。 not unrewarding perfunctorily, but calm attitude of life of unrestrained selfconfidence. Plain living, there is no noise noisy, no earthly troubles, more did not fill in the discontent of desire, some just a calm, a calm. 3, memory of heart will not good things to erase the, life is a When no movie, pain is a beginning, the struggle is a kind of process, death is a kind of ending. Give up this giving up is the helpless, do not give up the abandoned, do not give up this giving up is ignorance, do not give up should not give up is persistent. 4, a thing figured is heaven, think impassability is hell. Since the living, to live better. Sometimes we because of too narrowminded, too care around the chores and penny wise and pound foolish, not worth the candle. Some things to attract trouble and worry, pletely depends on how we look at and deal with it. Don39。t always take everything back to things, and don39。t get into a blind alley, don39。t want to face, don39。t be narrowminded. Poke to care, is