Chapter 2 : The Basics .

Voltage

From previous discussions , we have established that voltage is the energy which causes electrons to flow . Hence we can say that voltage is the amount of energy ( W ) required to move a charge (  Q ) form a certain point to another ,

V=W/Q

OHMS law

So lets say I have a circuit and it is connected to a voltage source V . I connect some load or resistor to the voltage source , with the help of some conducting wires. The voltage source will push charges in the wire, which will pass through load .

Now the relation between voltage and current can be represented by a formula formulated by Mr George Simon Ohms, hence laying the foundation of circuit analysis

V=I R

• Where V is voltage with units of volts
• I is current with units of Amperes
• And R is resistance with units of Ohms Ω

George Simon Ohm 16 March 1789 – 6 July 1854) a was German physicist and mathematician. As a school teacher, Ohm began his research with the new electrochemical cell, invented by Italian scientist Alessandro Volta. Using equipment of his own creation, Ohm found that there is a direct proportionality between the potential difference (voltage) applied across a conductor and the resultant electric current. This relationship is known as Ohm’s law

Example:

Now lets say we have a circuit

• · Find Current
• · Find Current when Voltage is doubled
• · Find Current when resistance is doubled

Work Power and Energy

Work is expenditure of energy to overcome some resistance for example , pushing a cart is a work, where energy is consumed for moving the cart.

Energy is defined as the ability to do work. Energy has the units of Joules . Whenever voltage passes through some resistance , its lossed some energy in form of heat .

If we use a material , which can loose a lot of energy we will end up making a bulb or a tea maker. For example it would take 90000 J to boil a cup of water

Power is the rate at which energy is consumed , or the rate of work at which energy is supplied .

Power has unit of watts , and is defined as

Power (P)=E/T

Now does it give you some idea, that how bulbs are rated 60 W, 25 W.

We can also define as power as product of voltage and current

P = V . I

Find power in rresistor

Remember . The amount of energy liberated by resistor is always equal to amount of energy applied.

Question Can you justify how power is product of voltage and current

Power Sign Conventions

Question : Does battery provide or absorb power ……

So we know power is supplied by battery. And current leaves positive terminal… So if current is leaving positive terminal of a element, it is said to be providing energy .

More discussion on active and passive devices, and sign convention is given in upcoming chapters

Type of Sources .

There are four types pf sources .

• Independent Voltage Source
• Independent Current Source
• Dependent Voltage Source
• Dependent Current Source

Well lets see your observation

Independent Ssources

An independent voltage source is a two-terminal element that maintains a specified voltage between its terminals regardless of the load and time

Similarly

An independent current source is a two-terminal element that maintains a specified voltage between its terminals regardless of the load and time

Dependent Sources

Unlike independent source , which are not effected by the change in circuit. Dependent sources depend directly on some other sources or elements in circuits