磁感应强度是一个矢量，磁场中某点磁感应强度的方向是-最需题库

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1以下关于电场线的说法，正确的是
A.电场线是电荷移动的轨迹
B.电场线是实际存在的曲线
C.电场线是闭合的曲线
D.电场线是起始于正电荷，终止于负电荷
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2电视机的荧光屏表面经常有许多灰尘，这主要的原因
A.电视机工作时，屏表面有静电而吸附灰尘
B.玻璃具有较强的吸附灰尘的能力
C.电视机工作时，屏表面温度较高而吸附灰尘
D.灰尘的自然堆积
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3下表为某电热水壶铭牌上的一部分内容. 根据表中的信息，可计算出在额定电压下以额定功率工作时通过电热水壶的电流约为<table style="BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; MARGIN: auto 6.75pt; BORDER-COLLAPSE: collapse; BORDER-TOP: medium none; BORDER-RIGHT: medium none; mso-table-layout-alt: fixed; mso-border-alt: solid windowtext .5pt; mso-table-lspace: 9.0pt; mso-table-rspace: 9.0pt; mso-table-anchor-vertical: paragraph; mso-table-anchor-horizontal: page; mso-table-left: 136.05pt; mso-table-top: 15.75pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt; mso-border-insideh: .5pt solid windowtext; mso-border-insidev: .5pt solid windowtext" border="1" cellspacing="0" cellpadding="0" align="left" _dj="MsoNormalTable"><tbody><tr style="PAGE-BREAK-INSIDE: avoid; mso-yfti-irow: 0; mso-yfti-firstrow: yes"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 84.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt" width="113">型号</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 84.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1.5pt double; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-right-alt: double windowtext 1.5pt" width="113">SP-988</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 84.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: double windowtext 1.5pt" width="113">额定功率</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 84.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt" width="113">1500 W</td></tr><tr style="PAGE-BREAK-INSIDE: avoid; mso-yfti-irow: 1; mso-yfti-lastrow: yes"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 84.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="113">额定电压</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 84.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt double; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-right-alt: double windowtext 1.5pt; mso-border-top-alt: solid windowtext .5pt" width="113">220 V</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 84.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: double windowtext 1.5pt; mso-border-top-alt: solid windowtext .5pt" width="113">额定容量</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 84.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="113">1.6 L</td></tr></tbody></table>
A.0.15 A
B.0.23 A
C.4.4 A
D.6.8 A
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4首先发现电流磁效应的科学家是
A.安培
B.奥斯特
C.库仑
D.麦克斯韦
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5下列哪种力是洛伦兹力
A.电荷间的相互作用力
B.电场对电荷的作用力
C.磁铁对小磁针的作用力
D.磁场对运动电荷的作用力
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6A为已知电场中的一个固定点，在A点放一电量为q的电荷，所受电场力为F，A点的电场强度为E，则（）
A.若在A点换上 –q，A点的电场强度将发生变化
B.若在A点换上电量为2q 的电荷，A点的电场强度将变为2E
C.若A点移去电荷q ，A点的电场强度变为零
D.A点电场强度的大小、方向与q 的大小、正负、有无均无关
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