Voltage or Potential Difference

To push Charges, for creating (flow of Charges) current. We need some force.

How this force is created?  This force is created due to potential difference

The charges or any other quantity always moves from higher potential to lower potential (in case of water , it is called pressure). Similar in our case, charges from higher potential moves to lower potential . In case of electricity this is called voltage

So now we have a reservoir of charges, (Battery). Some force is applied to move these charges (voltage). Now the moving charges (current) flow in some pipe (wire) and reaches destination (load e.g. bulb).

Voltage

The voltage (or potential difference) between two points is defined as one volt if it requires one joule of energy to move one coulomb of charge from one point to another.

Can Voltage be positive or negative? Yes it can be positive or negative (called polarity of voltage).

Battery

Find Potential Difference

Types of Voltage sources

1. A voltage source is a two terminal device which can maintain a fixedvoltage. An ideal voltage source can maintain the fixed voltage independent of the load resistance or the output current.

Battery

A battery is a device that converts chemical energy to electrical energy . A battery has a fixed life time , and depend upon the amount of current it supplies.

Life (hours) = ampere hour rating/Ampere of Current Produced

A battery with 60 A h rating can supply 1 Ampere for 60 Hours and 60 Amperes for 1 hour.

Generator

A generator is a device that converts mechanical energy into electrical energy. How ever the out put is AC .(will be discussed later)

Solar Cell

A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect

Conventional Current

The nice thing about standards is that there are so many of them to choose from

Initially when researches started developing formulas and started studying behavior of electronic circuits. They assumed that current moved from positive to negative terminal. So the standard was made accordingly. However later on it was discovered that the current is due to moving of charge from negative terminals to positive terminals .

But however the it was decided that same formulas will be used as they gave results accurately, and all theories were still accurate. The only difference was direction, which was changed. So it was decided to keep the same convention.

Drawing Circuits .

Any physical circuit can easily be represented by using symbols and schematics. Here is a list of symbols that are commonly used for electric circuit .

So lets say we have a battery that is connected to a bulb. And we need to redraw it so .

We may conclude that in the end every loads either a bulb, lamp or motor may be represented by a resistor. How ever many electrical components have their own symbols

Case Study 1

Charging a Car battery

There are several reasons your car battery could die 

1. Leaving your car for long period of times (without starting it)
2. Extreme temperatures
3. Leaving lights , ACs or any other load on for long time, when car is not in use

In order to charge a dead car battery, a set of jumper cables and a functional car with a charged battery is required

The positive terminal current leaves the positive terminal of charger or battery (Supplying energy ) and enter the positive terminal of dead battery absorbs it

Power

Power is a product of voltage and current , or amount of energy used to do a work .

Using the above equation we can easily derive Work done

Sign conventions for power

We know that a battery is represented some thing like this , where we assume or say that the battery have two terminals , positive and negative, and the power leaves the positive terminal of a battery

We know that power can be absorbed (like absorbed by by a bulb to give us light or by a fan to give us air) and can also be supplied , like by a battery .

So we need to summarize a way that can tell us that if the power is being absorbed or supplied . so a simple rule is stated below