大学物理大学物理下 (31).ppt

Explain how energy can be stored in a magnetic fieldDerive the expression for energy stored in a inductor Derive the the energy density in magnetic fieldObjectives4-7.Energy Stored in a Magnetic FieldCollege Physics II平台标位置预留Recall the energy stored in electric field:Using Ohms on it:Energy in capacitor:Density of energy:To get magnetic energy,consider a RL circuit:College Physics II平台标位置预留LR Multiply each term by idt and integrate over t,Energy stored in an inductor:If Wm is known,L can be obtained from this equation.College Physics II平台标位置预留Work done by the power sourceHeat generated by the resistorLR Take long solenoid as an example,The energy stored per unit volume of the field,density of energy,is:(magnetic energy density)In general,one can use:College Physics II平台标位置预留