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Wheatstone bridge, also known as the resistance bridge, is used to calculate the unknown resistance by balancing two legs of the bridge circuit, of which one leg includes the component of unknown resistance. It was invented by Samuel Hunter Christie in the year 1833, which was later popularized by Sir Charles Wheatstone in 1843.

The circuit is composed of two known resistors, one unknown resistor and one variable resistor connected in the form of a bridge. This bridge is very reliable as it gives accurate measurements.
 

Wheatstone bridge, also known as the resistance bridge, is used to calculate the unknown resistance by balancing two legs of the bridge circuit, of which one leg includes the component of unknown resistance. It was invented by Samuel Hunter Christie in the year 1833, which was later popularized by Sir Charles Wheatstone in 1843.

The circuit is composed of two known resistors, one unknown resistor and one variable resistor connected in the form of a bridge. This bridge is very reliable as it gives accurate measurements.

A Wheatstone bridge circuit consists of four arms of which two arms consists of known resistances while the other two arms consist of an unknown resistance and a variable resistance. The circuit also consists of a galvanometer and an electromotive force source. The emf source is attached between points a and b while the galvanometer is connected between the points c and d. The current that flows through the galvanometer depends on the potential difference across it.

A gold-leaf electroscope is a simple device which is used to identify the electric charge present in a body.Their operation is based on the principle of like sign charge repulsion. Two sheets or leaves, cut longer than they are wide and made of very thin, electrically conductive material, are hung adjacent and virtually in contact with each other. The leaves are ordinarily made of material sufficiently thin so that they have no rigidity and hang down limply. When the leaves, which are electrically connected, become electrically charged, they push apart from each other. The angle they form correlates on the amount of electric charge on the leaves. See the figure below. If the instrument is shielded so that the capacitance is fixed, then the angle can be with some precision to static voltage. It should be noted that the electroscope actually indicates potential, not charge.

The leaf electroscope does not distinguish positive from negative charge, though there are some simple methods for doing so.

In a calibrated electroscope, the two leaves are made of fine hammered gold leaf and the voltage is determined by viewing and measuring the separation angle with a low-power microscope

Fringe width:-

1. Fringe width is the distance between consecutive dark and bright fringes.
2. It is denoted by ‘β’.
3. In case of constructive interference fringe width remains constant throughout.
4. It is also known as linear fringe width.

Angular Fringe width:-

1. It is the angle subtended by a dark or bright fringe at the centre of the 2 slits.
2. It is denoted by ‘θ’.

• Mathematical Expression for fringe width(β):-
  • x_n =((nλD)/d)
  • x_n+1 =(((n+1)λD)/d)
  • β =x_n+1 - x_n
  • =(((n+1) λD)/d) – ((nλD)/d)
  • =>β = (λD/d)
  • Therefore fringe width depends on:-
    • (λ)Wavelength of the light used, (D) distance of the screen from the slits and (d) distance between two slits.
  • Mathematical Expression forangular fringe width(θ):-
    • θ =(β/D)
    • θ = (λD)/(d D)
    • θ = (λ/d)

According to the question the balls are having equal charges, and the strings are of the same length. When these balls are suspended from the string a force will act between these charges which are equal to where k is the dielectric constant of the material.
As plastic has been inserted between these two charges and plastic has a dielectric constant k greater than 1 and from the relation we can see that the force is inversely proportional to the dielectric constant thus the force will decrease when a plastic is inserted.

Kirchhoff’s First law: Junction law

• Junction Law is also known as Kirchhoff’s First Law.
• It states that at the junction,sum of current entering the junction is equal to the sum of current leaving the junction.
• Junction is any point in the circuit.
• Consider a case where I₁ and I₂are the currententering the junction and,currentI₄ and I₅ are exiting out of the junction.
• According to Kirchhoff’s law; I₁+ I₂ =I₃+ I₄+ I₅

Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of electric charge: positive and negative (commonly carried by protons and electrons respectively). Like charges repel each other and unlike charges attract each other. Electric charges are of two general types: positive and negative. Two objects that have an excess of one type of charge exert a force of repulsion on each other when relatively close together. For example, electrons have negative charge and protons have positive charge, but neutrons have zero charge.