Ch 9Current Electricity — Class 12 Physics, concept-first.

In Class XI you studied why materials conduct electricity in the first place -- the origin of electrical conductivity, especially in metals -- and you learned how to collapse a chain of resistors wire…

Before the two laws themselves can be stated precisely, three words that describe the LAYOUT of a circuit need fixed meanings, because Kirchhoff's laws are written in terms of exactly these three thin…

Kirchhoff's first law -- also called the current law or the junction law -- states that the algebraic sum of the currents meeting at any junction of an electrical network is zero:

Kirchhoff's second law -- the voltage law -- states that around any closed loop of an electrical network, the algebraic sum of every product of current and resistance (every 'IR' potential drop) toget…

Many physical quantities besides a wire's own material and geometry can shift the value of a resistance -- temperature, mechanical strain, humidity, the level of a liquid, and more all change how much…

The basic Wheatstone-bridge circuit of Section 9.3 is used, in practice, in several different physical forms, each built to determine some unknown resistance conveniently and precisely.

A voltmeter is the everyday device used to measure the potential difference between two points in a circuit.

A potentiometer consists physically of a long wire AB, of length L, resistance R and uniform cross-sectional area A, connected across a driving cell of emf and internal resistance r (together with a k…

Because the potential gradient K stays fixed once the driving cell, the wire and the rheostat setting are all fixed, an unknown potential difference can be measured simply by finding the LENGTH of wir…

Compared with an ordinary voltmeter, a potentiometer used at its balance point has three real merits. First, it is MORE SENSITIVE than a voltmeter -- a very small potential difference, of order V, can…

A galvanometer is a device built to detect weak electric currents flowing in a circuit. Inside it, a coil of fine wire is pivoted (or, in a more sensitive design, suspended) so that it can rotate free…

Turning a moving-coil galvanometer (MCG) into an ammeter -- an instrument for measuring current, connected in SERIES with the part of the circuit whose current is to be measured -- needs three things…

Turning a moving-coil galvanometer into a voltmeter -- an instrument for measuring potential difference, connected in PARALLEL with the part of the circuit across which the voltage drop is to be measu…

When an electric current is driven through a resistor, electrical energy is converted into thermal (heat) energy -- this is the everyday, familiar direction of the conversion.

If two different (dissimilar) metals are joined at two points to form a single closed loop, and these two junctions are then held at DIFFERENT temperatures, a small emf is produced within the loop and…

Sample papers and previous-year board questions for this subject.