IB Physics 12 Topic 5 – 2 Electro-statics & fields

The plan: Video clip of the day JSM Electro-statics Applets

JSM – Electro-statics Aohttp:// Ao Sims & Applets: hockeyhttp://phet.colorado.edu/en/simulation/electric- hockey

Electric Field Intensity: E is the Electric Field Intensity N/C F Q is the Electric ForceN q is the Electric ChargeC

Example Question: A particle with charge q = +2.0x10 -9 is placed in an electric field and it experiences a force of F Q =4.0x10 -9 N [W]. A) What is the electric field intensity at the location of the charge?

Example Question: A particle with charge q = +2.0x10 -9 is placed in an electric field and it experiences a force of F Q =4.0x10 -9 N [W]. B) Predict the force that would be experienced by a charge of q=+9.0x10 -6 C if it replaced the charge above.

a)

b)

Gravitational Field Intensity: g = Gravitational field intensity (N/kg) F g = Gravitational force (N) m = mass (kg)

Charged Particles Moving: MwxI4http:// MwxI4

A Point Charge: A point charge is an charged entity which occupies a minute point which is an ideal case. For practical purposes we consider it is a tiny charged body and the charge at a single point where all the charge is concentrated. We use point charges in the basic derivations of electrostatic equations which eliminates the complication of distribution and concentration of charge over the charged body.

Electric Field Intensity Near a Point Charge: E = Electric field intensity (N/C) k = Coulomb’s constant (Nm 2 / C 2 ) q = Source charge (C) r = Distance (m)

Gravitational Field Intensity Near a Point of Mass: g = Gravitational Field Intensity(N/kg) G = Universal Gravitational Constant (Nm 2 / kg 2 ) m s = Mass of source of field (Kg s ) r = Distance from center of source(m)

Video Resources: Newton’s Gravitational: – SAhttp:// SA Gravitational Fields: – x-8http:// x-8

Gravitational Field Lines: The gravitational field lines are directed radially inward toward a mass, m.

Magnetic Field Lines: The magnetic field lines are closed loops leaving the N-pole of the magnet and entering the S-pole.

Electric Field Lines: A) The electric field lines from positive charge +q are directed radially outward. (B) The electric field lines are directed radially inward toward negative point charge –q

Electric Field Lines: C) The electric field lines of an electric dipole are curved, and extend from the positive to the negative charge. At any point, such as 1, 2, or 3, the field created by the dipole is tangent to the line through the point.

Electric Field Lines: D) The electric field lines for two identical positive point charges are shown. If both of the charges were negative, the directions of the lines would be reversed.

In class discussion: 1.Briefly explain the following with relation to charged particles or points of mass. (a)action at a distance

In class discussion: 1.Briefly explain the following with relation to charged particles or points of mass. (a)action at a distance In the action-at-a-distance theory, an object is believed to exert a force directly on another object some distance away.

In class discussion: 1.Briefly explain the following with relation to charged particles or points of mass. (b) fields

In class discussion: 1.Briefly explain the following with relation to charged particles or points of mass. (b) fields A field is the influence that an object (mass, charge, or magnet) has on the properties of the space around it.

In class discussion: 1.Briefly explain the following with relation to charged particles or points of mass. (c) electric field intensity

In class discussion: 1.Briefly explain the following with relation to charged particles or points of mass. (c) electric field intensity Electric field intensity is the electric force exerted per unit charge at a point in space.

In class discussion: 1.Briefly explain the following with relation to charged particles or points of mass. (d) gravitational field intensity

In class discussion: 1.Briefly explain the following with relation to charged particles or points of mass. (d) gravitational field intensity Gravitational field intensity is the gravitational force exerted per unit mass at a point in space.

In class discussion: 1.Briefly explain the following with relation to charged particles or points of mass. (e)field lines

In class discussion: 1.Briefly explain the following with relation to charged particles or points of mass. (e)field lines Field lines indicate the direction of the field vectors throughout space, and their density indicates the strength of the field.

Question to do: 1)Calculate the gravitational field intensity at a height of km from Earth’s surface. 2)Challenge Question: Two point charges, +36  C and –28  C, are 15.0 cm apart in a vacuum. What is the electric field intensity at a point midway between them?

Question to do: 1)Calculate the gravitational field intensity at a height of km from Earth’s surface. 2)Challenge Question: Two point charges, +36  C and –28  C, are 15.0 cm apart in a vacuum. What is the electric field intensity at a point midway between them?