STPM Physics Chapter 12 Electrostatics

STPM Physics Term 2 Chapter 12 Electrostatics 1.

Coulomb’s law in air F= = qE

2.

Coulomb’s law in other medium with F=

3.

Electric field strength, E E=

Comparison with Gravitational law

Electric flux of one surface, = EA 10. Charged sphere and hollow sphere

=

*The direction of the electric field at a point is the direction of the force on a positive test charge placed at that point. *Inside the sphere: ∑

= 0, hence E = 0

11. Uniformly charged plane (2 Gaussian surfaces) ∑ = 2EA = E=

∑

*Charge density, = 12. Equipotential surface a. b. c.

4.

∑

All points on equipotential surfaces have same electric potential Equipotential surfaces are at right angles to electric field, E No work is done in moving a charge from one point to another point on same equipotential surface.

Acceleration of electron in uniform electric field. F = qE = ma a=

13. Linear motion equation Presence of acceleration Before Vx = V 0 Vy = 0 VR = V x

5.

After Vx = Vo Vy = uy + at VR = √

= V1

Absence of acceleration (no deviation) Before After Vx = V0 Vx = V0 Vy = 0 Vy = 0 VR = Vx VR = Vx

Charged particles tied on a string in an electric field. In equilibrium ∑ = T sin 30o – qE = 0 ∑ = T cos 30o – mg = 0

14. Applying sign of charge, q : 15. F and E Vector quantity Resultant based on Pythagoras theorem of xand y-compononent &

U and V Scalar quantity Resultant based on simple addition

= 30o =

6.

Electric potential, V =

7.

Electrical potential energy, U =

8.

Energy required to move a charged particle from one point to another point : U = q

9.

Gauss’ law :

=

∑

E= = qV

E=√

V=

(

+

+

)