Physical Science Second Semester Exam Study Guide Notes

Strategy for Exam Preparation

  • Read through the notes to refresh memory on topics.
  • Use the study guide as a starting point to identify areas needing more study time.
  • Refer to homework assignments, quizzes, and reviews for practice.
  • Utilize Google Classroom for notes, assignments, and reviews.
  • Mindset is critical for success; believe in your ability to perform well.
  • The semester exam is a multiple-choice test with 45 questions.

Electricity & Circuits

Conductors vs. Insulators

  • Conductors allow electricity to flow easily.
    • Metals are generally excellent conductors.
    • Tend to feel cold because they easily accept heat.
    • Also conduct heat (thermal energy).
  • Insulators resist the flow of electricity.
    • Tend to be light or have "air holes".
  • Electrical wires have a metal core (conductor) surrounded by insulation for protection.
  • Pure water is a poor conductor.
  • Sports drinks with salts and salt water are good conductors.
  • Electricity behaves similarly to water; water analogies can help understand circuits.

Circuits

  • Electricity flows through circuits: paths of conductors (usually wires).
  • Any break in the circuit causes it to fail.
  • A closed circuit has no breaks; the light lights up.
  • An open circuit has a break in it; the light will not light up.
  • Breaks can be small; paper, plastic, or air gaps can stop electricity flow.

Circuit Diagrams

  • Circuit diagrams are a simplified way to represent circuits.
  • Components include:
    • Wire: paths for electricity to flow (like pipes).
    • Battery: pushes electricity through the circuit (like a pump).
    • Light bulb: lights up and resists electricity (no water equivalent).
    • Switch: turns electricity on and off (like a valve).
    • Resistor: resists the flow of electricity (like a restriction in a pipe).
    • Capacitor
  • Important to pay attention to the direction of the battery in diagrams.

3 Quantities of a Circuit

  • Voltage: Electrical potential; the force pushing electrons.
    • Measured in Volts.
    • Linked to energy: 1 volt = 1 joule of energy per coulomb of charge.
  • Current: Flow of electrons through closed circuits.
    • Measured in Amps.
  • Resistance: Resists current flow; devices in the circuit provide resistance.
    • Measured in Ohms.
  • These three quantities are linked; changing one affects the others.

Types of Circuits

  • Series Circuits:
    • Only one path for electricity to flow.
    • If any part of the series circuit is broken, the entire circuit fails.
    • Example: Two lightbulbs in series; if one is unscrewed, both turn off.
  • Parallel Circuits:
    • Multiple paths for electricity to flow.
    • Branches are independent; if one path is broken, others remain on.
    • Example: Two lightbulbs in parallel; if one is unscrewed, the other stays on.
    • Houses are wired in parallel so each appliance can be controlled independently.

Ohm's Law

  • Current = \frac{Voltage}{Resistance}
  • I = \frac{V}{R}
  • Also expressed as: V = IR and R = \frac{V}{I}
  • Abbreviations:
    • A - Amps (current)
    • V - Volts (voltage)
    • $\Omega$ - Ohms (resistance)
  • Increasing voltage increases current.
  • Increasing resistance decreases current.
  • Decreasing voltage decreases current.
  • Decreasing resistance increases current.

Examples

  • How much current does a 12 V battery push through a 3$\Omega$ resistor?
    • V = 12V
    • R = 30 \Omega
    • I = \frac{12V}{30 \Omega} = 0.4 A
  • How strong a battery produces 2A through 3$\Omega$ resistor?
    • I = 2A
    • R = 30 \Omega
    • V = IR = (2A)(30 \Omega) = 60V

Current

  • Moving electrons (moving charge).
  • Increasing current causes more electricity to move through a device.
  • Increased electricity through a device makes it work faster (motor) or brighter (lightbulb).

Voltage

  • Electrical potential; the amount of work a battery can do.
  • Linked to energy: 1 volt = 1 joule of energy per coulomb of charge.
  • Increase voltage by using a stronger battery or adding batteries.

Resistance

  • Slows down current (like a dam holding back water).
  • Adding devices in a circuit increases resistance.

Examples Demonstrating Ohm's Law and Series Circuits

  • Scenario 1: One 6V battery and one lightbulb with 3$\Omega$ resistance.
    • I = \frac{V}{R} = \frac{6V}{3 \Omega} = 2A
    • The light is bright because the 6 volts only have one light to run.
  • Scenario 2: Two 1.5V batteries facing opposite directions (0V total) and one lightbulb with 3$\Omega$ resistance
    • No current, light is off.
  • Scenario 3: Two 3V batteries facing the same direction (6V total) and two lightbulbs in series, each with 3$\Omega$ resistance (6$\Omega$ total).
    • I = \frac{V}{R} = \frac{6V}{6 \Omega} = 1A
    • Both lights are dimmer because the 6 volts have to power two lights.

Magnets

Magnet Basics

  • A magnet is anything that can attract or repel another magnet.
  • Types: Bar, horseshoe, donut magnets.
  • All magnets have two poles: North (N) and South (S).
  • You cannot separate a N pole from a S pole; you just make smaller magnets.
  • Magnets exert magnetic forces of attraction and repulsion.
  • Opposites attract (N-S).
  • Likes repel (N-N, S-S).
  • Magnets only attract ferrous metals: Iron, Cobalt, and Nickel (steel is mostly Iron and Nickel).

How do Magnets Work?

  • Moving or spinning electrons in atoms cause magnetism.
  • If electrons are paired and spinning in opposite directions, the magnetism cancels out.
  • In magnetic substances, many electrons spin in the same direction.

Permanent vs. Temporary Magnets

  • Permanent Magnets: Do not lose their magnetism.
    • Many electrons spin the same way, and their small magnetic fields add up.
    • Lodestone and Magnetite are the only two natural permanent magnetic materials.
  • Temporary Magnets: Become magnets only when near a permanent magnet.
    • Electrons align when a magnet is near, but fall back randomly after the magnet is removed.
    • Only ferrous materials can become temporary magnets.
    • Bumping or dropping them can cause the electrons to fall back quickly.

Electromagnets

  • A magnet made by moving electricity.
  • Useful because they allow creating forces that can be turned on and off at will.
  • Example: Toaster uses an electromagnet to hold toast down.
  • An electromagnet does not have to have a core; any loops of electricity create a magnetic field.

Ways to Strengthen an Electromagnet:

  1. Add electricity (more current or more batteries).
  2. Add more coils (more loops of wire).
  3. Add a ferrous core, especially iron, which becomes a temporary magnet.

Generators and Motors

  • Generators generate electricity.
  • Motors use electricity.
  • Moving electricity creates magnetic fields; moving magnets make electricity.
  • Because electricity and magnetism are linked, we can make motors and generators.

Generators

  • Something turns the generator (does work), causing magnets to move, which creates electricity.
  • Examples: Dams, cars, and power plants.
  • Work in (turning) yields electricity out.

Motors

  • Electricity causes magnetic forces through electromagnets.
  • The electromagnets cause the object to turn (do work).
  • Electricity in yields work out (moving air).

Motor or Generator?

  • It could be either, depending on how it is used.
  • Any motor can create electricity, and any generator will turn if electricity is applied.

Light and the Electromagnetic Spectrum

Light: Wave or Particle?

  • Evidence for Wave Nature:
    • Light is refracted in lenses and reflected by mirrors.
    • Two fingers close together cause lines of darkness (destructive interference).
  • Evidence for Particle Nature:
    • Light can travel through the vacuum of space, but a wave cannot.
  • Conclusion: Light is both a wave and a particle.

Photon

  • A light packet is called a photon.

Speed of Light

  • c = 3 \times 10^8 m/s
  • Light can circle the earth 7.5 times in one second.
  • The speed of light is the ultimate speed limit; nothing can go faster.

Where Does Light Come From?

  • Photons (light) come from electrons falling from high energy electron orbits to low orbits.
  • Each element has a different number of protons, so each element has slightly different electron energy levels and gives off different colors.
  • This allows determining the chemical makeup of stars by analyzing their light spectrum.

Visible Light

  • White light is made up of many different colors, each with a different wavelength and frequency.
  • A prism separates light by dispersion.
  • Different wavelengths (colors) refract (bend) differently when passing into glass.
  • The acronym "ROY G BIV" represents the colors of the rainbow: Red, Orange, Yellow, Green, Blue, Indigo, Violet.

Colors Have Different Energies

  • Different color flames give off different amounts of heat.
  • Red flames are cooler, and blue flames are hotter.
  • As you move from Red to Blue, light GAINS energy.
  • White light is made up of all colors, so a white flame is the hottest.

The Atom

The Periodic Table

Chemical Bonding