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/m^{2}.

→ 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 (V_{d}).

→ 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 m^{2}s^{-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 V_{ext} across R is given by V_{ext} = I(R + r) where r is internal resistance of the source.

→ In series connection of resistors, total resistance R_{s} = R_{1} + R_{2} + …………. + R_{n}

→ 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 R_{4} = R_{3} × \(\frac{\mathrm{R}_2}{\mathrm{R}_1}\)

→ 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, V_{d} = \(\frac{\mathrm{eE} \tau}{\mathrm{m}}\)

→ I = neA V_{d} 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,

R_{s} =R_{1} + R_{2} + R_{3} + ………….

→ 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, ε_{i} = 0

→ Kirchhoff’s second law. εE = εIR

→ Wheat stone bridge principle,

\(R_4=R_3 \times \frac{R_2}{R_1}\)