Question

某電場(chǎng)中有A、B、C三點(diǎn)，三點(diǎn)的電勢(shì)分別是φ_A=5V，φ_B=﹣2V，φ_C=0，現(xiàn)有一電荷量q=﹣6×10^﹣6C的點(diǎn)電荷P，求：                                                                                                                                 

①該點(diǎn)電荷在A、B、C三點(diǎn)的電勢(shì)能各為多大？                                                        

②若將P從A移到B，則靜電力做功多少？電勢(shì)能變化了多少？                                   

③若將P從B移到C，則靜電力做功多少？電勢(shì)能變化了多少？                                   

                                                                                                                                   

Answer 1

       解：①由題可知電勢(shì)φ_A＞φ_C＞φ_B，而沿電場(chǎng)線的方向電勢(shì)降低．則電場(chǎng)線的方向由A指向B．

點(diǎn)A的電勢(shì)能為：E_PA=qφ_A=﹣6×10^﹣6C×5V=﹣3×10^﹣5J

點(diǎn)B的電勢(shì)能為：E_PB=qφ_B=﹣6×10^﹣6C×（﹣2）V=﹣1.2×10^﹣5J

點(diǎn)C的電勢(shì)能為：E_PC=qφ_C=﹣6×10^﹣6C×0V=0

②AB兩點(diǎn)間電勢(shì)差U₁=φ_A﹣φ_B=7V，負(fù)電荷受電場(chǎng)力的方向由B指向A，電荷從A移到B點(diǎn)的過(guò)程中，電場(chǎng)力做負(fù)功，電荷的電勢(shì)能增大．

W₁=U₁q=7V×（﹣6×10^﹣6C）=﹣4.2×10^﹣5J，電勢(shì)能增大了4.2×10^﹣5J

③BC兩點(diǎn)間電勢(shì)差U₂=φ_B﹣φ_C=﹣2V，負(fù)電荷受電場(chǎng)力的方向由B指向C，電荷從B移到C點(diǎn)的過(guò)程中，電場(chǎng)力做正功，電荷的電勢(shì)能減小．

W₂=U₂q=﹣2V×（﹣6×10^﹣6C）=1.2×10^﹣5J，電勢(shì)能減小了1.2×10^﹣5J．

答：①該點(diǎn)電荷在A、B、C三點(diǎn)的電勢(shì)能分別為﹣3×10^﹣5J、﹣1.2×10^﹣5J、0；

②若將P從A移到B，則靜電力做功﹣4.2×10^﹣5J，電勢(shì)能增大了4.2×10^﹣5J；

③若將P從B移到C，則靜電力做功1.2×10^﹣5J，電勢(shì)能減小了1.2×10^﹣5J．