Ch. 10 Electricy and Magnetism

table of contents

Electric Circuits

An electric circuit is a pathway for the movement of electric charge, consisting of voltage source, connecting pipes, and other components

Current

Current is the movement of electric charge.

I= Q/t

I: current

Q: charge

t: time

Resistance

It’s resistance, different materials have different resistance. Metals are conductors (and have less resistance) and rubber is an insulator (and has more resistance).

Resistance and Resistivity

R= ρ L/A

• R: Electrical resistance, measured in ohms (Ω).

• ρ (rho): Electrical resistivity of the material, measured in ohm-meters (Ω⋅m).

• l: Length of the conductor, measured in meters (m).

• A: Cross-sectional area of the conductor, measured in square meters (m²).

Ohm’s Law

V=I/R

Resistors

A resistor is a component in an electric circuit that has a specific (and usually known) resistance.

Electric circuits may contain one resistor, but it’s more likely that they’ll have two or more. There are two ways the MCAT will combine resistors, in series or parallel. Tow or more resistors are said to be in series if each follows the others along a single connection in a circuit

resistors in series: each resistor follows the others along a single path in a circuit. For example, these two resistors are in series, because R2 directly follows R1 along a single path.

resistors in parallel: two or more resistors are said to be in parallel if they provide alternative routes from one point in a circuit to another.

DC Circuits

The simplest circuit consists of a voltage source (most commonly, a battery), a connecting wire between the terminals of the voltage source, and a resistor.

Direct current (DC) circuits have electric charge that flows in one constant direction. They use a steady voltage source, like a battery or solar cell, to push electrons through a closed path of wires and parts like resistors. [1, 2, 3, 4, 5, 6]

Basic Parts and Rules

• Voltage (V): The push that makes electricity move, measured in volts.

• Current (I): The flow of electrical charge, measured in amps.

• Resistance (R): How much a part slows down the flow, measured in ohms.

• Ohm's Law: Voltage equals current times resistance (V = I × R).

Power Dissapted by a Resistor: Joule Heating Law

P= I² R

Power

P=IV

Measuring Circuit Values

Capacitor

Charge on a capacitor

Q=CV

Capacitance of a Parallel Plate Capacitor

C=ε₀A/d

Ed’s formula

V=Ed

Electrical PE Stored in a Capacitor

PE= 1/2QV

Capacitance of a Parallel-Plate Capacitor with a Dielectric

C_{with dielectric}= K x C_{without dielectric}= Kε₀A/d

Combinations of Capacitors

parallel

series

Alternating Circuit

Direct Circuit (DC)

Alternating Circuit (AC)

Magnetic Fields and Forces

Sources of Magnetic Fields