[单选题]
An electron enters a region of magnetic field with a velocity as shown in the diagram. The path followed by the electron is shown by the dotted line. What is the direction of the magnetic field in this region?
A. Out of the plane of the paper
B. Into the plane of the paper
C. Towards the right
D. Towards the left
参考答案: B
本题详细解析: Explanation:
The force acting on the electron is downward at entry and perpendicular to the velocity, and the electron has negative charge. Using conventional methods (right-hand/left-hand) the magnetic field vector points into the plane of the paper
