Electric field dd

GOOD MORNING!!!

PHYSICS

ANALOGY

The electric field is the space around an electrical charge

just like

a gravitational field is the space around a mass.

POSITIVE TEST CHARGE it is a positive charge which is so small that

the force it exerts does not significantly alter the distribution of the other charges,the ones that cause the field being measured …

Use sometimes ‘‘POINT CHARGE’.’

POINT CHARGE It is as an idealized charged particles with no

real size or spatial extent.This will allow us todraw electricfield lines without needing to consider the size of the charge.

ELECTRIC FIELD LINES

ELECTRIC FIELD LINES FOR A POSITIVE POINT CHARGE

The arrows show that a positive test charges would experievce a force radially OUTWARD FROM THE POINT CHARGE.All of the begin at the ‘‘same distence from the point charge.’’

All lines have the same length even though they are POINTING IN DIFFERENT DIRECTIONS.The magnitude of the foce is the same at each locations that are the same distance away from the point charge.

POSITIVE POINT CHARGE

ELECTRIC FIELD LINES FOR A NEGATIVE POINT CHARGES

If the point charge is negative,then the positive test charge would be attracted towards it.In that case,the lines of force point radially INWARD TOWARDS THE NEGATIVE CHARGE.

NEGATIVE POINT CHARGE

What is the difference?

Electric Field Lines of two Same Sign Charges

The electric field lines point from the charges.There is an ABSENCE OF LINES in the region between the charges.This indicates that the FIELD IS RELATIVELY WEAK BETWEEN THE CHARGES.If the two charges had been negative,the pattern of the field lines would be the same as the one for two positive charges,but the field lines would point towards the negative charges.

Electric Field Lines of two Same Sign Charges

Electric Field Lines of two Opposite Charges

It is also called ELECTRIC DIPOLE,two point charges that are opposite in sign but equal in magnitude.

Electric Field Lines of two Opposite Charges

IMPORTANT FEATURES OF ELECTRIC FIELD LINES

1.Always begin on a positive charge and end on anegative charge,and do not start or atop the region between.

2.The number of lines leaving a positive charge or entering negative charge is proportional to the magnitude of the charge.

3.‘‘the more lines there are in a given location,the stronger the field is in that region’’

4.The direction of the electric field at any given points is the vector drawn tangents to the electric field line at that point.

‘‘THE LONGER THE ELECTRIC FIELD VECTOR,THE STRONGER THE ELECTRIC FIELD.’’

Conductors and Electric Fields (under electrostatic conditions)“The electric field is zero inside a charged conductor”.

“Excess charge on an isolated conductor resides on the surface”.

“Excess charge accumulates on sharp points”.

Electric field lines meet the conductor perpendicular to the surface of the conductor.

Which field is stronger?A B

Electric Field for a Point ChargeUsing E=F/qo and Coulomb’s Law

prove:

E = k Q

______

r2

where Q is the central charge.

Example1A test charge of +3µC is located 5m to the

east of a -4µC charge.A) Find the electric force felt by the test

charge.B) Find the electric field at that location.

ANSWER :

4.32x10-3 N, 1.44 x 103 N/C along the –x axis.

Example 2Calculate the electric field felt by a test

charge located half way between a charge of +1C and a charge of -3C, that are 2m apart.

ANSWER :

1.8 x 1010 N/C

EXERCISES:If a test charge is moved to a location three times

as far as its original location, how does the electric field change?

Q equal to -2.0 x 10 to the power of -6 C,R is equal to 20 cm ,k is equal to 9 x 10 to the power of 9 N squared of m over the squared of coulomb.. Find the E or electric field strength…

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