Students can go through AP Inter 2nd Year Physics Notes 6th Lesson Current Electricity will help students in revising the entire concepts quickly.
AP Inter 2nd Year Physics Notes 6th Lesson Current Electricity
→ The rate of flow of charge through any section of the conductor is called strength of the electric current and is measured in ampere i = \(\frac{\mathrm{Q}}{\mathrm{t}}\)
→ Ohms law: A constant temperature, the current passing through a conductor is proportional to the potential difference between its ends. V ∝ I or V = IR where R is resistance of a conductor or resistor.
→ Resistor is a device that opposes the flow of current through it.
→ The direction of conventional current is from high to low potential and is opposite to the direction of electron flow.
→ The resistors which obey Ohm’s law are called Ohmic resistors.
→ The resistors which does not obey ohm’s law are called non-ohmic resistors.
→ Specific resistance is the resistance of a wire of unit length and unit area of cross-section. ρ = \(\frac{\mathrm{RA}}{l}\). Unit of specific resistance is Ω m.
→ Current per unit area (I/A) is called current density (j). It’s unit is A/m2.
→ Reciprocal of resistance is called conductance and measured in Siemen.
→ Reciprocal of resistivity is called conductivity and measured in Simen/meter σ = \(\frac{1}{\rho}\)
→ The ratio of increase in resistance for 1°C rise of temperature to its resistance at 0°C is called temperature coefficient of resistance (α).
→ The fractional change in resistivity per unit change in temperature is called temperature coefficient of resistivity.
→ The work done per unit charge is called emf of a cell E = \(\frac{\mathrm{W}}{\mathrm{q}}\) and measured in volts.
→ The resistance offered by the electrolyte in the cell for the flow of charges is known as internal resistance.
→ emf developed inside the cell opposes the flow of charges in the circuit is called back emf.
→ The speed with which an electron gets drifted in a metallic conductor under the application of an external electric field is called the drift velocity (Vd).
→ The average drift velocity resulting, from the application of unit electric field strength is called mobility (μ). μ = \(\frac{V_d}{E}\) It’s unit is m2s-1 volt-1.
→ The flow of electricity in liquids is called electrolysis and constituted by the motion of ions.
→ The flow of electricity in gases is called discharge and constituted by the motion of ions.
→ When a source of emf E is connected to an external resistance R, the voltage Vext across R is given by Vext = I(R + r) where r is internal resistance of the source.
→ In series connection of resistors, total resistance Rs = R1 + R2 + …………. + Rn
→ In parallel connection of resistors, total resistance is given by
\(\frac{1}{\mathrm{R}_{\mathrm{P}}}=\frac{1}{\mathrm{R}_{\mathrm{I}}}+\frac{1}{\mathrm{R}_2}+\ldots \ldots \frac{1}{\mathrm{R}_{\mathrm{n}}}\)
→ Kirchhoffs junction rule: At any junction of circuit elements, the sum of currents entering the junction must equal the sum of currents leaving it.
→ Kirchhoffs loop rule: The algebraic sum of changes in potential around any closed loop must be zero.
→ Principle of wheat stones bridge is R4 = R3 × \(\frac{\mathrm{R}_2}{\mathrm{R}_1}\)
→ Meter bridge works on the principle of Wheat stone bridge.
→ Using meter bridge unknown resistance can be measured accurately.
→ Potentiometer is more sensitive and measures accurate potential differences.
Formulae
→ Current I = \(\frac{\mathrm{q}}{\mathrm{t}}=\frac{\mathrm{ne}}{\mathrm{t}}\)
→ Drift velocity, Vd = \(\frac{\mathrm{eE} \tau}{\mathrm{m}}\)
→ I = neA Vd also I = \(\frac{\mathrm{nAe}^2 \tau}{\mathrm{m}} \mathrm{E}\)
→ Electron mobility, m = \(\frac{e \tau}{m}\)
→ Current density, j = \(\frac{\mathrm{I}}{\mathrm{A}}\)
Also j = \(\frac{\mathrm{ne}^2 \tau}{\mathrm{m}} \mathrm{E}\)
→ Ohm’s law, V = IR
→ Resistance, R = \(\frac{\mathrm{V}}{\mathrm{I}}\) Also R = \(\frac{\rho \mathrm{l}}{\mathrm{A}}\)
Also R = \(\frac{\mathrm{m}}{\mathrm{ne}^2 \tau} \cdot \frac{1}{\mathrm{~A}}\)
And ρ = \(\frac{m}{n e^2 \tau}\)
→ Conductance G = \(\frac{1}{\mathrm{R}}\)
Resistivity σ = \(\frac{1}{\rho}\)
→ Temperature coefficient of resistivity
α = \(\frac{\mathrm{R}-\mathrm{R}_0}{\mathrm{R}_0 \theta}\)
→ Colour code of carbon resistance
→ For series connection,
Rs =R1 + R2 + R3 + ………….
→ For parallel connection,
\(\frac{1}{R_p}=\frac{1}{R_1}+\frac{1}{R_2} \ldots \ldots . .\)
→ Terminal PD or terminal voltage
V = E – Ir = \(\left[\frac{E-V}{V}\right] R\)
→ From Kirchhoff’s first law, εi = 0
→ Kirchhoff’s second law. εE = εIR
→ Wheat stone bridge principle,
\(R_4=R_3 \times \frac{R_2}{R_1}\)