Electricity and Magnetism Notes
Electricity and Magnetism
Study of electric and magnetic phenomena. Focus on energy transfer by electrical transmission (TT) and electromagnetic radiation (TER).
Laws are crucial in devices like smartphones and electric motors.
Interatomic and intermolecular forces are electric in origin, forming the basis of chemistry and biological organisms.
Electricity and magnetism were linked in the 19th century by Oersted (compass deflection near current) and Faraday/Henry (current induced by moving a wire near a magnet).
Maxwell formulated electromagnetism laws in 1873, as fundamental as Newton's laws.
Electric Fields
Deals with electric forces between objects with electric charge, Coulomb's law, electric fields, and electric potential energy.
Key differences between electric and gravitational forces:
Electrical situations can have various shapes; gravity is mostly spherical.
Motion of objects in electric fields (e.g., electrons) is easily controllable compared to objects in gravitational fields.
Electricity can be turned on/off; gravity is always present.
Electric field strength is adjustable; Earth's gravitational field isn't.
Some materials conduct electricity, others don't; gravity is universal.
Electric field-free regions can be created; gravity is always there.
1 Properties of Electric Charges
Electric force is observed through simple experiments (e.g., balloons attracting paper). Two types of charges exist: positive and negative (Franklin's convention).
Like charges repel; opposite charges attract.
Electric charge is conserved in an isolated system; electrification is charge transfer.
Electric charge is quantized: q = \pm Ne, where e = 1.602 18 \times 10^{-19} C
2 Charging Objects by Induction
Electrical conductors allow free electron movement; insulators do not. Semiconductors have intermediate properties.
Induction charges an object without contact. Grounding involves a reservoir (like Earth) for accepting/providing electrons.
Insulators experience charge realignment within molecules, creating surface charge and attraction.
3 Coulomb's Law
Coulomb's law quantifies electric force between stationary charged particles (point charges): F = ke \frac{|q1||q2|}{r^2}, where k = 8.9876 \times 10^9 N \cdot m^2/C^2 or k=\frac{1}{4\pi\epsilon0} and \epsilon_0 = 8.8542 \times 10^{-12} C^2/N \cdot m^2 (permittivity of free space).
Smallest unit of free charge: e = 1.602 18 \times 10^{-19} C (electron or proton charge magnitude).
Electric force is conservative like gravity.
Vector form: \overrightarrow{F}{12} = ke \frac{q1q2}{r^2} \hat{r}{12} (force exerted by q1 on q_2).
Superposition principle applies when multiple charges are present; net force is the vector sum of individual forces.
4 Analysis Model: Particle in a Field (Electric)
Electric field (E) is the electric force per unit charge: \overrightarrow{E} = \frac{\overrightarrow{F}}{q_0} (N/C).
Force on arbitrary charge q in electric field E: \overrightarrow{F} = q\overrightarrow{E} (N).
Electric field due to source charge q: \overrightarrow{E} = k_e \frac{q}{r^2} \hat{r} (positive q: radially outward; negative q: radially inward).
Total electric field from multiple source charges: \overrightarrow{E} = ke \sumi \frac{qi}{ri^2} \hat{r}_i
Electric Dipole: A positive charge q and a negative charge -q separated by a distance 2a.
5 Electric Field Lines
Visual representation of electric fields, where:
E is tangent to the field line at each point.
Line direction matches E direction (force on positive charge).
Line density is proportional to E magnitude.
Rules for drawing electric field lines:
Lines begin on positive charges, terminate on negative charges or infinity (if net charge exists).
The number of lines is proportional to the charge magnitude.
No two field lines can cross.
6 Motion of a Charged Particle in a Uniform Electric Field
Force on charge q in uniform electric field E: \overrightarrow{F} = q\overrightarrow{E}
Acceleration: \overrightarrow{a} = \frac{q\overrightarrow{E}}{m} (constant if E is uniform).
Can apply kinematic equations if E is uniform.