Chapter – 7 DC CIRCUITS

1. Electromotive Force2. Single-loop currents3. Multi-loop circuits4. Energy in circuits5. The RC circuit

1) Everyday use several electronic devices, such as cell phone, computer, MP3, TV, microwave oven, etc.

2) All these devices have electrical circuits.

3) The basic science of electrical engineering is physics.

4) So here we study physics of electric circuits. Electric circuits are combinations of resistors and batteries.

Importance

Joule’s Law of Heating

Heat produced in a given resistance in a given time t is

H i 2

t R These are known as Joule’s laws.

Find the heat developed in each of the three resistors in 1 minute.

Exercise – 1

Solution

Battery Electromotive Force (emf) Battery

1. For steady flow of charge carriers through the resistor, potential difference between ends of the device must be established.

2. Need a device that maintains a potential difference.

3. We call such a device an emf device.

4. A common emf device is the battery.

5. Examples of emf devices are: Electric generator, HP Battery, solar cells, Hydrogen fuel cells.

Within the Battery device (or source), positive charge carriersmove from a region of low Electric ( - ve terminal ) to theregion of higher electric potential ( at positive terminal). The strength of the source is measured in terms of theelectromotive force (emf).

emf

Mathematical expression of emf

In a real circuit we have to take the internal resistance Ri of the source into account. The internal resistance Ri of the source can be considered as connected in series to an ideal emf.

Internal Resistance of a battery

Exercise - 2 Find the current i and potential difference a and b terminals .

Solution

Single-loop currents (Kirchhoff's rule )

Multi-loop circuits

The procedure used to calculate the current flowing through a complicated circuit (with several resistors and emfs) is called the loop method.

Procedure: Loop Method

Analysis

Energy in circuits