Presentation Topic 2: Electricity and Magnetism (2.2: Motion of Charged…
Presentation Topic 2: Electricity and Magnetism
2.1: Electric Fields
Electrostatically charged objects exert forces upon one another; the magnitude of these forces can be calculated using Coulumb's Law.
Solve problems involving the use of F=1/(4πε_0 ) ((q_1 q_2)/r^2)
Using proportionality, discuss changes in the magnitude of the force on each of the charges as a result of a change in one or both of the charges and/or a change in the distance between them
Explain that the electric forces are consistent with Newton's Third Law.
When more than two point charges are present, the force on any on of them is equal to the vector sum of the forces due to each of the other point charges.
Use vector addition in one dimension or two dimensions with right-angled, isosceles, or equilateral triangles to calculate the magnitude and direction of the force on a point charge due to two other point charges
Point charges and charged objects produce electric fields in the space that surrounds them. A charged object in an electric field experiences an electric force.
The direction and number of electric field lines per unit area represent the direction and magnitude of the electric field
Sketch electric field lines for an isolated positive or negative point charge and for two point charges.
Sketch electric field lines between and near the edges of two finite oppositely charged parallel plates
A positively charged body placed in an electric field will experience a force in the direction of the field; the field strength of the electric field is defined as the force per unit charge.
Solve problems involving the use of E ⃗=F ⃗∕q
Using Coulomb's Law, derive the formula: F=1/(4πε_0 ) q/r^2
Solve problems using: F=1/(4πε_0 ) q/r^2
There is no electric field inside a hollow conductor of any shape, provided that there is no charge in the cavity.
Sketch the electric field produced by a hollow spherical charged conductor.
Electric fields are strongest near sharp points on conductors. These fields may be large enough to ionise the polar and non-polar molecules in the air near the sharp points, resulting in charge movement away from the conductor. This is called a ‘corona discharge’.
Sketch the electric field produced by a charged pear-shaped conductor.
Describe how the electric field near sharp points may ionise the air.
2.2: Motion of Charged Particles in Electric Fields
When a charged body moves or is moved from one point to another in an electric field and its potential energy changes, work is done on or by the field.
The electric potential difference, (∆ V), between two points is the work done per unit charge on a small positive test charge moved between the points, provided that all other charges remain undisturbed.
The electronvolt (eV) is a unit of measurement which describes the energy carried by a particle. It is the work done when an electron moves through a potential difference of 1 volt.
Solve problems involving the use of W=q∆ V
Convert energy from joules into electronvolts and vice versa.
The magnitude of the electric field (away from the edges) between two oppositely charged parallel plates a distance 'd' apart, where ∆ V is the potential difference between the plates, is given by the formula: E=∆V/d
Solve problems involving the use of E=∆V/d
The force on a charged particle moving in a uniform electric field is constant in magnitude and direction, thus producing a constant acceleration.
Derive the formula a = qE/m for the acceleration of a charged particle in an electric field
Solve problems using a = qE/m and the motion formulae for the movement of charged particles parallel or antiparallel to a uniform electric field.
Describe the motion of charged particles parallel or antiparallel to a uniform electric field.
In a cyclotron, the electric field in the gap between the dees increases the speed of the charged particles.
Describe how an electric field between the dees can transfer energy to an ion passing between them.
Describe how ions could be accelerated to high energies if they could be made to repeatedly move across an electric field.
Calculate the energy transferred to an ion each time it passes between the dees.
Explain why the ions do not gain kinetic energy when inside the dees.
When a charged particle moves at an angle to the uniform electric field the component of the velocity perpendicular to the field remains constant.
Compare the motion of a projectile in the absence of air resistance with the motion of a charged particle in a uniform electric field.
Solve problems for the motion of charged particles that enter a uniform electric field perpendicular to the field.
Solve problems for the motion of charged particles that enter a uniform electric field at an angle to the field where the displacement of the charged particle parallel to the field is zero.