Electric Field Concept By Engr Hinesh Kumar Lecturer

Electric Field Concept By: Engr. Hinesh Kumar Lecturer I. B. T, LUMHS

Electric Charge The effects of electric charge were first observed as static electricity: After being rubbed on a piece of fur, an rod acquires a charge and can attract small objects.

Electric Charge Charging both amber and glass rods shows that there are two types of electric charge; like charges repel and opposites attract.

Electric Charge All electrons have exactly the same charge; the charge on the proton (in the atomic nucleus) has the same magnitude but the opposite sign:

Electric Charge Definition Electric charge is a physical property of matter that causes it to experience a force when close to other electrically charged matter. There are two kinds of charge. Properties of Charges like charges repel unlike charges attract charges can move + -

The Concept of a Field A field is defined as a property of space in which a material object experiences a force. P m Above earth, we say there is a gravitational field at P. . F Because a mass m experiences a downward force at that point. No force, no field; No field, no force! The direction of the field is determined by the force.

What is a Field? n In physics, a field is a physical phenomena that has a value everywhere in space. n Loudness has a value everywhere around a stereo. n This means you can describe the loudness with a field. n All interactions between matter and energy occur by way of fields.

Fields and energy n Any field is a form of energy that is distributed through space. n A magnetic field has energy because it can exert force over distance, or do work, on another magnet.

Adding fields n Fields of the same kind can be added or subtracted. n The field from an electromagnet can either cancel the field from a permanent magnet or add to it.

Electric Field n Electric field is defined as the electric force per unit charge. n The direction of the field is taken to be the direction of the force it would exert on a positive test charge. n The electric field is radially outward from a positive charge and radially in toward a negative point charge

Electric Field Here, q 0 is a “test charge” – it serves to allow the electric force to be measured, but is not large enough to create a significant force on any other charges.

Electric Field If we know the electric field, we can calculate the force on any charge: The direction of the force depends on the sign of the charge – in the direction of the field for a positive charge, opposite to it for a negative one.

Drawing the Electric Field n Electric field lines follow the direction of the force on a positive test charge. n The strength of the electric field is shown by the spacing of the field lines. n The field is strong where the field lines are close together and weak where the lines are far apart.

Electric Field Lines The charge on the right is twice the magnitude of the charge on the left (and opposite in sign), so there are twice as many field lines, and they point towards the charge rather than away from it.

Electric Field Lines Combinations of charges. Note that, while the lines are less dense where the field is weaker, the field is not necessarily zero where there are no lines. In fact, there is only one point within the figures below where the field is zero – can you find it?

Answer n the field from a collection of charges is simply the vector sum of the fields from the individual charges. To find the places where the field is zero, simply add the field from the first charge to that of the second charge and see where they cancel each other out n According to this explanation: n Field is zero in figure 3. n http: //physics. bu. edu/~duffy/py 106/Electricfield. html