Proton:An elementary particle with a positive charge, found in the nucleus of an atom.  A proton is over a thousand times heavier than an electron.Protons and neutrons make up most of an atom's mass.

Neutron:An elementary particle without an electrical charge, one of the building blocks of the nucleus of the atom. A neutron has about the same mass as a proton.

Electron:An electron is a negatively charged subatomic particle. It can be either free (not attached to any atom), or bound to the nucleus of an atom. Electrons in atoms exist in spherical shells of various radii, representing energy levels.

Potatoes naturally contain salt, one of the most important ingredients for conducting electricity.Water is contained naturally in potatoes. The water helps the salt in the potato break apart into separate ions. Water found in potatoes is not pure water and will conduct electricity because of the contaminants and ions contained in the potato. Water combines with salt to produce electrolytes, a key ingredient in conducting electricity. Every potato contains cells. These cells are in the form of water and salt.The electricity travels through these other cells because of the water and salt.

Lightning is a sudden electrostatic discharge that occurs during a thunderstorm. This discharge occurs between electrically charged regions of a cloud (called intra-cloud lightning or IC), between two clouds (CC lightning), or between a cloud and the ground (CG lightning).

Lightning is an electric current. When the ground is hot, it heats the air above it. This warm air rises. As the air rises, water vapour cools and forms a cloud. When air continues to rise, the cloud gets bigger and bigger. In the tops of the clouds, temperature is below freezing and the water vapour turns into ice. Now, the cloud becomes a thundercloud. Lots of small bits of ice bump into each other as they move around. All these collisions cause a build up of electrical charge. Eventually, the whole cloud fills up with electrical charges. Lighter, positively charged particles form at the top of the cloud. Heavier, negatively charged particles sink to the bottom of the cloud. When the positive and negative charges grow large enough, a giant spark , called lightning  occurs between the two charges within the cloud. This is like a static electricity sparks you see, but much bigger.

Most lightning happens inside a cloud, but sometimes it happens between the cloud and the ground. A build up of positive charge builds up on the ground beneath the cloud, attracted to the negative charge in the bottom of the cloud. The ground's positive charge concentrates around anything that sticks up  trees, lightning conductors, even people.The positive charge from the ground connects with the negative charge from the clouds and a spark of lightning strikes.

In a homogeneous transparent medium light travels in a straight line and this is known as rectilinear propagation of light.

Light rays are actually electromagnetic waves. There are oscillating electric and magnetic fields perpendicular to the direction of propagation of light. The disturbance or the wave is always up and down about a straight line. That line is the axis of the wave. It is also the direction of propagation of the wave.

Example:Shadows generated when light is blocked by an object.

Kirchhoff's circuit laws are two equalities that deal with the current and potential difference (commonly known as voltage) in the lumped element model of electrical circuits. They were first described in 1845 by German physicist Gustav Kirchhoff.[1] This generalized the work of Georg Ohm and preceded the work of Maxwell. Widely used in electrical engineering, they are also called Kirchhoff's rules or simply Kirchhoff's laws.

Both of Kirchhoff's laws can be understood as corollaries of the Maxwell equations in the low-frequency limit. They are accurate for DC circuits, and for AC circuits at frequencies where the wavelengths of electromagnetic radiation are very large compared to the circuits.