D' = ρv it simply says that the source for the D' field is the volume charged density and you have the 4th equation which says that ∇.
D' = ρv है। यह बताता है कि' D क्षेत्र का स्रोत आयतन आवेश घनत्व है और आपके पास चौथा समीकरण है जो कहता है कि ∇.