Correlation is a statistical tool which studies the relationship between two variables e.g. change in price leads to change in quantity demanded.
Correlation studies and measures the direction and intensity of relationship among variables. It measures co-variation not causation. It does not imply cause and effect relation.

Type of Correlation
Correlation is classified into positive and negative correlation. The correlation is said to be positive when the variables move together in the same direction. e.g. sale of lce cream and temperature move in same direction.
The correlation is said to be negative when the variables move in opposite direction. e.g. When you spend more time in studying chances of your failure decline.

Electric Current is the flow of electrons. But an electric Circuit is the closed path in which electric current flows.

• When an electric current flows through a wire, the wire gets heated. It is the heating effect of current or When current flows through a metal wire it gets heated up, this is called heating effect of current. E.g. a glowing electric bulb becomes warm. This effect has many applications like Electric Heater, Light Bulb etc.
• When an electric current flows through a wire, it produces magnetic effect around it. A current carrying coil of an insulated wire wrapped around a piece of iron is called an electromagnet. Magnetic Effect of electric current has many applications like Electric Bell, Motor, Fan etc

Auxins

• IAA and indole butyric acid (IBA) have been isolated from plants and NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) are synthetic auxins.
• They help to initiate rooting in stem cuttings, promote flowering, prevent fruit and leaf drop at early stages, induce parthenocarpy (example- tomato).
• In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance.
• Auxins are widely used as herbicides.

Example- 2, 4-D is widely used to kill dicotyledonous weeds.

Gibberellins

• Gibberellins are denoted as GA₁, GA₂, GA₃.
• All gibberellins are acidic.
• They help to increase in length of axis, elongate and improve shape of fruits, delay senescence,
• Spraying juvenile conifers with GAs hastens the maturity period, thus leading to early seed production.
• Gibberellins also promotes bolting, defined as internode elongation just prior to flowering, in beet, cabbages.

Cytokinins

• Cytokinins were discovered as kinetin from the autoclaved herring sperm DNA.
• Natural cytokinins are synthesised in regions where rapid cell division occurs, for example, root apices.