Учебное пособие Казань-2016 Сайфуллина М. Н., Хабирова Н. М. English for Physicists
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Posobie dlya fizikov Habirova Sajfullina ispravv
| Force on a moving charge
If a charge moves through a magnetic field at an angle, it will experience a force. The equation is given by F = q v × B or F = qvB sin θ, where q is the charge, B is the magnetic field, v is the velocity, and θ is the angle between the directions of the magnetic field and the velocity; thus, using the definition of the cross product, the definition for the magnetic field is . Magnetic field is expressed in SI units as a tesla (T), which is also called a weber per square meter: The direction of F is found from the right ‐ hand rule, shown in Figure 1. Using the right-hand rule you can find the direction of magnetic force on a moving charge. To find the direction of the force on the charge, with a flat hand point your thumb in the direction of the velocity of the positive charge and your fingers in the direction of the magnetic field. The direction of the force is out of the palm of your hand. (If the moving charge is negative, point your thumb opposite to its direction of motion.) Mathematically, this force is the cross product of the velocity vector and the magnetic field vector. If the velocity of the charged particle is perpendicular to the uniform magnetic field, the force will always be directed toward the center of a circle of radius r, as shown in Figure 2. The x symbolizes a magnetic field into the plane of the paper - the tail of the arrow. (A dot symbolizes a vector out of the plane of the paper - the tip of the arrow.) The magnetic force provides centripetal acceleration: , or The radius of the path is proportional to the mass of the charge. This equation underlies the operation of a mass spectrometer, which can separate equally ionized atoms of slightly different masses. The singly ionized atoms are given equal velocities, and because their charges are the same and they travel through the same B, they will travel in slightly different paths and can then be separated. жүктеу/скачать 1,1 Mb. Достарыңызбен бөлісу:
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