**Superposition:****Diffraction** refers to the bending or spreading out of waves when they travel through a small opening or when they pass round a small obstacle.

The **Principle Of Superposition** states that when two waves of the same kind meet at a point in space, the resultant displacement at that point is the vector sum of the displacements that the two waves would separately produce at that point.

**Interference** refers to the superposing of two or more coherent waves to produce regions of maxima and minima in space, according to the principle of superposition.**Gravitation:****Newton’s Law Of Universal Gravitation** states that every particle in the Universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

**Gravitational field strength** at a point is defined as the gravitational force per unit mass acting on a mass placed at that point.

**Gravitational potential energy**, U of a point mass m, in a gravitational field, is the work done by an external force in bringing that point mass from infinity to that point.

**Gravitational potential** at a point in a gravitational field is the work done per unit mass, by an external force, in bringing the mass from infinity to that point.

**Escape speed** is the minimum speed with which a mass should be projected from the Earth’s surface in order to escape Earth’s gravitation field.

The **coulomb’s law** states that the electrostatic force between two point charges is proportional to the product of their charges and inversely inversely proportional to the square of the distance between them.

The **Electric field strength** at a point in an electric field is the electrostatic force per unit charge experienced by a small positive test charge placed at that point.

**Electric Potential** at a point in an electric field is the work done per unit charge by an external agent in bringing a positive test charge from infinity to that particular point without acceleration.

**Electric potential energy** of a charge in an electric field is defined as the work done by an external force in bringing the charge from infinity to that point a distance r away.

The **electron volt** is defined as energy that an electron (or proton) gains (or loses) when it is accelerated(or decelerated) through a potential difference of 1 volt.**Current Of Electricity:****Electric Current** is the rate of flow of charge through a particular cross sectional area with respect to time.

The **potential difference** between two points in an electrical circuit is the electrical energy converted into other forms of energy per unit charge passing from one point to the other.

**One volt** is the potential difference between two points in an electrical circuit when one joule of electrical energy is converted to other form of energy as one coulomb of charge passes from one point to the other.

**Ohm’s Law** states that the ratio of the potential difference across a conductor to the current flowing through it, is a constant, provided that its physical conditions, such as temperature, remain constant.

The **electromotive force** ($\epsilon$) of a source is the energy converted from other forms to electrical per unit charge delivered round a complete circuit.

**Internal resistance** (r) of any real source is the resistance that charge moving through the material of the source encounters.

**DC Circuits:****Kirchhoff’s First Law** states that the total current entering a junction is equal to the total current leaving the junction. OR The algebraic sum of currents at a junction is zero.

**Kirchhoff’s second law** states that the net electromotive force around a closed circuit loop is equal to the sum of potential drops around the loop. OR The algebraic sum of the changes in potential encountered in a complete traversal of a closed circuit loop must be zero.

** Electromagnetism:****Magnetic flux density** (B) is defined as the force acting per unit current per unit length on a wire placed at right angles to the magnetic field.

**1 Tesla** is defined as the magnetic flux density of a uniform magnetic field when a wire of length 1m , carrying a current of 1A, placed perpendicular to the field, experiences a force of 1N in a direction at right angles to both the field and the current.

**Electromagnetic Induction:****Magnetic flux through a plane surface** is the product of the magnetic flux density normal to the surface BN and the area A of the surface.

The **weber** is defined as the magnetic flux through a surface if a magnetic field of flux density 1 T exists perpendicularly to an area of 1 m^{2}.

**Magnetic Flux Linkage** is defined as the product of the number of turns N of the coil and the magnetic flux linking each turn.

**Faraday’s Law** states that the induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage or rate of cutting of magnetic flux linkage.

**Lenz’s Law** states that the induced e.m.f. will be directed such that the current which it causes to flow opposes the change that is producing it.

The definitions for waves aren’t correct since a lot of them assume that the waves require a medium. The definitions as a whole are correct but a lot wouldn’t get you the marks in an exam.

powerful definitions ..like them

I learn alot from you guys

what of charge density?

EL PENE