principles

seebeck effect

In 1821, German Physicist Thomas Johann Seebeck discovered that in a circuit consisting of two dissimilar metals like iron and copper, an emf is developed when the junctions are maintained at different temperatures

Peltier effect

In 1834, a French scientist Peltier discovered that when electric current is passed through a circuit consisting of two dissimilar metals, heat is evolved at one junction and absorbed at the other junction. This is called Peltier effect. Peltier effect is the converse of Seebeck effect.

tangent law

A magnetic needle suspended at a point where there are two crossed fields at right angles to each other will come to rest in the direction of the resultant of the two fields

galvanometer into voltmeter

A galvanometer can be converted into a voltmeter by connecting a high resistance in series with it. The scale is calibrated in volt

coulomb's law

Coulomb's law states that the force of attraction or repulsion between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between4 them. The direction of forces is along the line joining the two point charges.

cyclotron

Cyclotron is a device used to accelerate charged particles to high energies. It was devised by Lawrence. Principle Cyclotron works on the principle that a charged particle moving normal to a magnetic field experiences magnetic lorentz force due to which the particle moves in a circular path.

kirchoff's i law

Kirchoff's current law states that the algebraic sum of the currents meeting at any junction in a circuit is zero.

kirchoff's ii law

Kirchoff's voltage law states that the algebraic sum of the products of resistance and current in each part of any closed circuit is equal to the algebraic sum of the emf's in that closed circuit. This law is a consequence of conservation of energy.

moving coil galvanometer

Moving coil galvanometer is a device used for measuring the current in a circuit. Principle Moving coil galvanometer works on the principle that a current carrying coil placed in a magnetic field experiences a torque.

right hand palm rule

The coil is held in the right hand so that the fingers point in the direction of the current in the windings. The extended thumb, points in the direction of the magnetic field.

fleming's left hand rule

The forefinger, the middle finger and the thumb of the left hand are stretched in mutually perpendicular directions. If the forefinger points in the direction of the magnetic field, the middle finger points in the direction of the current, then the thumb points in the direction of the force on the conductor.

thomson effect

Thomson suggested that when a current flows through unequally heated conductors, heat energy is absorbed or evolved throughout the body of the metal.

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Two dissimilar metals connected to form two junctions is called thermocouple. The emf developed in the circuit is thermo electric emf. The current through the circuit is called thermoelectric currenteffect is called thermoelectric effect or Seebeck effect. If the hot and cold junctions are interchanged, the direction of current also reverses. Hence Seebeck effect is reversible. In a Cu-Fe thermocouple (Fig 3.2a), the direction of the current is from copper to iron at the hot junction

end rule

When looked from one end, if the current through the solenoid is along clockwise direction Fig 3.18a, the nearer end corresponds to south pole and the other end is north pole. When looked from one end, if the current through the solenoid is along anti-clock wise direction, the nearer end corresponds to north pole and the other end is south pole

galvanometer into ammeter

a galvanometer is converted into an ammeter by connecting a low resistance in parallel with it.

coefficient of mutual induction

coefficient of mutual induction of two coils is numerically equal to the magnetic flux linked with one coil when unit current flows through the neighbouring coil. If e s is the induced emf in the coil (S) at any instant of time, then from the laws of electromagnetic induction,

joule's law

for a steady current I, the amount of heat produced in time t is H = VIt ...(1) For a resistance R, H = I 2 Rt ...(2) and H = 2 V R t ...(3) The above relations were experimentally verified by Joule and are known as Joule's law of heating. By equation (2) Joule's law implies89 that the heat produced is (i) directly proportional to the square of the current for a given R (ii) directly proportional to resistance R for a given I and (iii) directly proportional to the time of passage of current. Also by equation (3), the heat produced is inversely proportional to resistance R for a given V

corona discharge.

the leakage of electric charges from the sharp points on the charged conductor is known as action of points or corona discharge. This principle is made use of in the electrostatic machines for collecting charges and in lightning arresters (conductors).

biot savart law

According to Biot and Savart, the magnetic induction dB at P due to the element of length dl is Fig 3.9 Magnetic field due to a circular loop carrying current d di f l it n o er c o P A B dl Y X I r O Fig 3.10 Biot - Savart Law98 (i) directly proportional to the current (I) (ii) directly proportional to the length of the element (dl ) (iii) directly proportional to the sine of the angle between dl and the line joining element dl and the point P (sin θ) (iv) inversely proportional to the square of the distance of the point from the element ( 2 1 r ( ∴ dB α 2 I d sin θ r l dB = K 2 I d sin θ r l , K is the constant of proportionality The constant K = µ 4π where µ is the permeability of the medium. dB = µ 4π 2 I d sin θ

one ampere

Ampere is defined as that constant current which when flowing through two parallel infinitely long straight conductors of negligible cross section and placed in air or vacuum at a distance of one metre apart, experience a force of 2 × 10 -7 newton per unit length of the conductor.

maxwell cork screw rule

If a right handed cork screw is rotated to advance along the direction of the current through a conductor, then the direction of rotation of the screw gives the direction of the magnetic lines of force around the conductor.

ohm's law

The law states that, at a constant temperature, the steady current flowing through a conductor is directly proportional to the potential difference between the two ends of the conductor. (i.e) I α V

ampere's law

The line integral v∫ → B. → dl for a closed curve is equal to µ o times the net current I o through the area bounded by the curve.

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The mass of a substance liberated at an electrode by a given amount of charge is proportional to the *chemical equivalent of the substance. If E is the chemical equivalent of a substance, from the second law m α E

faraday's laws

The mass of a substance liberated at an electrode is directly proportional to the charge passing through the electrolyte. If an electric current I is passed through an electrolyte for a time t, the amount of charge (q) passed is I t. According to the law, mass of substance liberated (m) is m α q or m = zIt