Electricity:- Part 2

Electric potential and potential difference 

-> The work done to move a unit positive charge from infinity to a particular point in electric field is called electric potential.

                    

* It is a scalar quantity and its SI unit is volt (V). 

* “Volt” named after an Italian scientist Alessandro Volta (1745-1827). 

-> Potential difference- The amount of work done of moving a unit positive charge from one point to the other point in an electric field is called a potential difference. It is also a scalar quantity and its SI unit is volt (V).

                         

Note 

* In a cell, a chemical reaction produces a potential difference between the two terminals of the cell. As a result, the positive charge flows from higher potential to lower potential and the negative charge flows from lower potential to higher potential. 

* Charge flows in a circuit due to difference in potential between the two points.

                   

Since Work is measured in joule and charge in coulomb So, Volt is also written as JC-1 or J/C. 

* One Volt- if one joule of work is done to move one coulomb of electric charge from one point to another point is called One Volt.  

                                                

-> For a positively charged body, the potential is positive, and for a negatively charged body, potential is negative.  

* Potential difference or electric potential is measured by voltmeter. 

Voltmeter 

-> The instrument which is used to measure the potential difference half conductor of the conductor is called a voltmeter. 

   A voltmeter is always connected in parallel across the points between which the potential difference is to be measured. 

-> While connecting a voltmeter in a circuit, its positive terminal should be connected to the positive terminal of the battery and its negative terminal should be connected to the negative terminal of the battery.

Note 

* The resistance of an ideal voltmeter is infinity. 

* The resistance of an ideal ammeter is zero.  

-> Galvanometer- it is an instrument which is used to detect weak current in a circuit. It is connected in series in a circuit. 

   It does not have a positive or a negative terminal and it can also, detect the direction of current in a circuit. 

Note- A galvanometer can detect only small currents. Thus, to measure large currents, it is converted into an ammeter. It can be converted into an ammeter by connecting a low resistance called shunt resistance in parallel to the galvanometer.                     

-> A resistor having a very low value of resistance is called shunt resistance.  

Symbols of electrical elements used in electric circuit  

* Rheostat- It is a variable resistor whose resistance can be varied. 

Ohm’s Law

-> when physical conditions like temperature, the intensity of light etc. remains the same then the current flowing through a conductor is directly proportional to the potential difference across it ends. 

  If ‘V’ is the potential difference across the ends of a conductor and ‘I’ is the current through it. Then, According to ohm's law 

              

Mathematical expression of ohm's law

                

* Resistance- The property of a conductor that opposes the flow of electric current when passing through it, known as Resistance. 

* It is the ratio of the potential difference applied between the ends of a conductor and the current flowing through it. 

* It is a constant quantity. 

* Its SI unit is ohms, symbolized by the Greek letter ‘omega’ (Ω).

* It arises due to the collision of drifting electrons within the conductor. 

* Resistance causes electrical energy to be dissipated (उडा देना) as heat. 

* The value of Resistance (Constant) depends on nature, length, area of 

cross-section and the temperature of the conductor.

           

Q) What is the cause of electrical resistance? 

-> Resistance is caused due to the collision of free electrons with the metal ions of the conductor. When the temperature increases, the metal ions have more energy and vibrate. This increases the frequency of collisions between free electrons and the metal ions, and therefore increasing the resistance.

Q) What are the side effect of electrical resistance? 

-> Electric current is able to create severe burns in the body. The reason is hidden in the power dissipation across the body´s electrical resistance. Shock can cause cardiac problems, burns to tissues and organs, muscle spasms, serious effects to the nervous system, and other unexpected consequences. 

Q) What happens when an electric current passes through the human body? 

-> When current flows through the human body, it can cause a lot of problems such as Currents as low as 10 mA can cause severe muscle contractions and burns, while currents of 20 mA or greater can cause paralysis of the muscles that allow you to breathe.

Q) What is the purpose of resistance?

-> The role of resistance is to limit the flow of charge (or current). Sometimes resistance is intentionally kept in the circuit to limit the current in that circuit. 

  It is the same as tap, which is intentionally kept to limit the flow of water. 

* 1 ohm- The resistance of a conductor when potential difference of 1 volt is applied to it ends in which one ampere of current flows through it, called 1 ohm. 

So,