Important Derivations for Class 12 Physics Chapter 8 Electromagnetic Waves

Important Derivations for Class 12 Physics Chapter 8 Electromagnetic Waves (1) Derive expression for displacement current The electric flux between the plates of a capacitor is given by $$ \begin{aligned} & \phi_{\mathrm{E}}=\mathrm{EA}=\frac{\mathrm{Q}}{\varepsilon_0 \mathrm{~A}} \cdot \mathrm{A}=\frac{\mathrm{Q}}{\varepsilon_0} \\ & \quad \frac{\mathrm{d} \phi_{\mathrm{E}}}{\mathrm{dt}}=\frac{\mathrm{d}}{\mathrm{dt}}\left(\frac{\mathrm{Q}}{\varepsilon_0}\right)=\frac{1}{\varepsilon_0} \frac{\mathrm{dQ}}{\mathrm{dt}} \\ & \quad \frac{\mathrm{d} \phi_{\mathrm{E}}}{\mathrm{dt}}=\frac{1}{\varepsilon_0} \mathrm{i} \quad \quad\left(\text { As, } \mathrm{i}=\frac{\mathrm{dQ}}{\mathrm{dt}}\right) \\ & … Read more

Important Derivations for Class 12 Physics Chapter 6 Electromagnetic Induction

Important Derivations for Class 12 Physics Chapter 6 Electromagnetic Induction (1) Derivation of Emf induced in a rod moving in a uniform magnetic field. The magnetic flux linked with the area SPQR is: $$ \phi_R=B A \cos \theta=B l x \cos 0=B l x $$ As the rod PQ is moving towards left with a … Read more

Important Derivations for Class 12 Physics Chapter 3 Current Electricity

Important Derivations for Class 12 Physics Chapter 3 Current Electricity Deduction of Ohm’s law. When a potential difference ‘V’ is applied across a conductor of length ‘l’, the drift velocity in terms of ‘V’ is given by $$ v_d=\frac{e E \tau}{m}=\frac{e V \tau}{m l} $$ If the area of cross-section of the conductor is ‘A’ … Read more

Important Derivations for Class 12 Physics Chapter 2 Electrostatic Potential and Capacitance

Important Derivations for Class 12 Physics Chapter 2 Electrostatic Potential and Capacitance Derivations Related to Potential due to an Electric Dipole Derivation 1: Electric potential due to electric dipole at a point on its axial line. Solution: Let ‘P’ be an axial point at distance ‘r’ from the centre of the dipole. Electric potential at … Read more

Important Derivations for Class 12 Physics Chapter 7 Alternating Current

Important Derivations for Class 12 Physics Chapter 7 Alternating Current Derivations Related to A.C. Applied Across an Inductor Derivation 1: (1) An ac voltage, V = V0 sin wt, is applied across a pure inductor L. Obtain an expression for the current I in the circuit and hence obtain the(i) inductive reactance of the circuit, … Read more

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