Science Teaching: Electricity, Magnetism & Waves

electrical conductor

moves electrons
electrons move freely
most metals

electrical insulators

electrons stay close to nuclei
wood, glass, plastic air

High-voltage power lines are constructed using metal wires mounted on wooden poles. Which of the following explanations best reflects the reasoning behind this design choice?
a) wooden poles decrease resistance in the wires
b) wooden poles act as insulators between the wires and the ground
c) wooden poles help keep the wires cool
d) wooden poles make thew ires vibrate less

b) wooden poles act as insulators between the wires and the ground

wave

disturbance that moves through space and time
carry energy from one place to another but do not carry matter

electromagnetic waves

vibrations of electric and magnetic fields
do not need a medium (material that carries wave)

period

time it takes to complete one full wave cycle (seconds)

medium

material that carries a mechanical wave
sound wave: air, water, et
electromagnetic waves: can travel without medium

wavelength

length of one complete wave cycle (top of one wave crest to the top of the next wave crest)

frequency

number of full cycles that happen each second
high frequency: short period, vibrates rapidly
low frequency: long period, vibrates slowly

wave speed

how fast energy moves from one place to another

speed of electromagnetic wave in a vaccuum

same as speed of light

wave speed equation

speed= wavelength x frequency

wave period equation

1/frequency

transverse wave

direction of the vibrate is perpendicular to the direction the energy travels
vibration is up/down or side/side when wave travels forward
looks like hills and vallesy

crests

peaks of the transverse wave

troughs

valleys of the transverse wave

amplitude

describes how far the medium moves in each direction as it vibrates from its normal, non-vibrating position
distance from center of wave to crest
greater energy = greater amplitude

longitudinal wave

direction of vibration is parallel to the direction the energy travels
sound waves

what determines wave speed?

the medium

fast wave speed due to…

strong molecular bonds in the medium
lower density mediums
warmer temperatures

Two identical sound waves are traveling through different materials. One travels through warm air, and the other travels through cold air. Which of the following statements best explains why the sound wave moves faster in warm air?
a) The sound wave in warm air has a higher frequency than the sound wave in cold air.
b) The molecules in warm air have more energy and return to their normal positions more quickly.
c) Warm air allows sound waves to have a larger amplitude.
d) Sound waves always move faster when the air is less dense, regardless of temperature.

b) The molecules in warm air have more energy and return to their normal positions more quickly.

Doppler Effect

when observer or object approach, wavelength is shorter, while frequency and pitch are higher

blueshift

when a glowing object moves toward an observer- frequency shifts toward the blue end of the spectrum (shorter wavelengths, higher frequencies) when object and observer approach each other

redshift

when a glowing object moves away from an observer

what is light

a form of electromagnetic radiation
has photons and a transverse wave

photon

light particles

sources of light

radiation of electromagnetic waves including visible light
electron transitions/excited electrons

how does excited electron give off light

when electrons return from excited state to ground state, they release energy (light)

amount of energy carried by light depends on…

frequency and amplitude

higher frequency for a given amplitude, the more energy it carries
higher amplitude for a given frequency, the more energy

shortest wavelength visible light

highest frequency
violet

highest wavelength visible light

lowest frequency
red

violet wavelength

~400 nm

blue wavelength

~475 nm

green wavelength

~525 nm

yellow wavelength

~580nm

orange wavelength

~600 nm

red wavelength

650 nm

Which of the following statements best explains why we can see visible light?
a) Visible light is the only type of electromagnetic radiation stars like the Sun can produce.
b) Visible light is the strongest of all electromagnetic radiation.
c) Visible light carries energy that our eyes can detect and turn into signals for the brain.
d) Visible light is the only form of electromagnetic radiation capable of acting like particles.

c) Visible light carries energy that our eyes can detect and turn into signals for the brain.

what emits electromagnetic waves

everything above 0K

lowest frequency electromagnetic specrtrum

highest wavelength
radio waves

highest frequency on electromagnetic spectrum

lowest wavelength
gamma rays

lowest to highest frequency electromagnetic spectrum

radio, microwave, infrared, visible light, ultraviolet, x-rays, gamma ray

Which of the following statements best explains how visible light fits into the electromagnetic spectrum?
a) Visible light is the only type of radiation humans can see because it has the highest energy of all electromagnetic waves.
b) Visible light is separate from the electromagnetic spectrum and is produced only by the Sun.
c) Visible light includes all electromagnetic waves that give off heat, such as infrared and microwaves.
d) Visible light is one part of the electromagnetic spectrum and falls between infrared and ultraviolet in frequency.

d) Visible light is one part of the electromagnetic spectrum and falls between infrared and ultraviolet in frequency.

Refraction

light changes speed and direction when moving at an angle from one material to another
bending light/colors: like in a prism to separate the colors

surfaces appear colored because…

surface absorbs certain frequencies (colors) and reflect others. Color seen is reflected color(s)

white light

combination of all light frequencies/colors

specular light reflection

in a mirror- all light rays stay in order and reflection looks like the image that produced it

diffuse light reflection

rougher surfaces
bumps in a surface scatter the light rays in many directions, image is lost

lens in optical systems

camera, microscope, human eye
use both refraction and reflection to record and project visual images

A teacher shines a flashlight onto classroom objects to demonstrate how light behaves on different surfaces. Students notice that the mirror shows a clear image of the flashlight, but the painted wall shows no image at all. Based on these observations, which of the following statements best explains what is happening with the light?
a) The mirror reflects light specularly, but the wall scatters too much light for the image to be seen.
b) The mirror reflects light diffusely, but the painted wall shows no image because it reflects all frequencies of light evenly, just like a white surface.
c) The mirror and the wall reflect light diffusely.
d) The mirror and wall do not reflect light.

a) The mirror reflects light specularly, but the wall scatters too much light for the image to be seen.

plane mirror

a flat mirror- produces a virtual image

law of reflection

the angles of incidence and angles of reflection are equal

normal line

line perpendicular to the surface

diverge

spread apart (light reflecting on a surface)

concave mirror

mirror that curves inward (away from looker in the middle)
produces enlarged image when object is farther than one focal length from the mirror, or a virtual image when 1 foal length awayconv

convex mirror

curves outward (toward object in center)
produces smaller image

refraction

light ray bending
when light travels across the boundary between two different materials (like air and glass)

when light crosses the boundary between two of these: air, glass or water, the angle of refraction is smallest in _____ and greatest in _____

smallest: glass (light density high)
greatest: air (light density low)

convex lense

“converging lens”
thicker in the center- bring light from one side of the lens to a focus on the other side of the lens
produce larger. upside down real image

magnifying glasses, telescopes, microscope lenses

concave lens

diverging lens
thinner in the center- causes light rays to diverge
smaller, upright virtual image

camera viewfinder

Diffraction

bending and spreading of a wavefront after it passes by or through an obstruction

AM radio waves vs FM radio waves

AM wave diffract more around big objects - less distortion from buidlings

dispersion

spreading of white light into its constituent colors

When white light enters a triangular glass prism, the different colors within it bend by different amounts. This causes the colors to spread out instead of staying combined. What is the name of this effect?
a) reflection
b) diffuse scattering
c) absorption
d) dispersion

d) dispersion

opaque

materials absorb light and do not allow the light to pass through (Cannot see through)

what happens to light when absorbed in opaque object?

energy carried by light enters and heats the material by increasing the kinetic energy of vibrations of particles in the material

transparent

light passes through object (water, glass)-can see through
light frequencies do not match the natural frequencies of the particles int he material, allowing light to go through

magnetism

force due to electron motion

electricity

flow of electrons (current) or the buildup of charge (static electricity)

how does static cling work

when electron from one material rub off and onto the other material, the objects are then oppositely charged and cling together

electric current is produced when…

a chemical reaction in a battery produces electrons that repel each other, causing them to flow
a magnet is moved in relation to a wire, and the magnetic force causes electrons to flow

do neutral material attract other materials?

Yes, positive and negatively charged objects

balloon rubbed on wool- gathers electrons and becomes negative

electromagnet

electrons allowed to flow through coils

A student is investigating why a compass needle moves when it is brought near a bar magnet. The student notices that the needle always lines up in the same direction when placed near the magnet. This behavior helps the student understand how magnetic fields influence nearby objects. Which statement best explains why the compass needle moves?
a) The needle spins because the magnet pushes air around it, causing it to turn.
b) The compass needle moves because the magnet adds an electric charge to the needle, making it rotate.
c) The needle turns because gravity pulls it toward the stronger end of the magnet.
d) The needle rotates because its own magnetic field aligns with the magnetic field of the bar magnet.

d) The needle rotates because its own magnetic field aligns with the magnetic field of the bar magnet.

total resistance of a series circuit

add them all together

Ohm’s Law equation

V=IR (V=voltage, R= resistance, I= current)

battery power equation

P=IV (P=power, I= current, V=voltage)

junction (circuit)

where a single path breaks into two or more paths- only a part of the current flows through each resistor

series vs parallel circuits

series has a greater total resistance
serries has greater current drawn from the battery
series has less total power supplied by battery

Capacitor

electronic devices that store charge
made from two conducting plates separated by an insulator (dielectric)c

capacitance

measure of the amount of charge on each plate in the capacitor after it has been connected to a voltage

C= Q/V c= capacitance, q=charge, v=voltage (unit: microfarad uF)

capacitance from capacitor geometry equation

C=(epsilom E)A/d

C= capacitance
E= dielectric constant
A= area overlap of two conducting plates
d= distance between plates

increasing the overlapping area of a capacitors plates ____ capacitance

increases

DC

direct current- flows in a single direction along each wire

flows from positive terminal to negative terminal (actual electrons move from negative to positive)
cell phone chargers and other devices

AC

alternating current- flows back and forth through each wire

power lines

During a classroom demonstration, a science teacher shows students two circuits:

Circuit 1: A battery powering a small incandescent bulb

Circuit 2: A generator set to output a 60 Hz sine wave, which is also powering an identical bulb

The teacher points out that in Circuit 1, the current flows in the same direction at all times, while in Circuit 2, the bulb still lights even though the generator's current reverses direction many times each second. What is the key difference between AC and DC that this demonstration is showing?
a) AC always provides more power than DC when using identical light bulbs.
b) DC rapidly switches direction, but AC flows in only one constant direction.
c) AC changes direction periodically, while DC flows steadily in one direction
d) AC cannot power incandescent bulbs, but DC can.

c) AC changes direction periodically, while DC flows steadily in one direction

battery composition

have two terminals made from different materials and an electrolyte that reacts chemically with the terminalst

type of chemical reaction in a battery

REDOX, ending with charged compounds/elements

flow in a battery

negative to positive (current)

battery exothermic or endothermic

exothermic

electromagnetic induction

electricity is created by forcing a conductor to move through a magnetic field
magnetic field interaction with electrons in wire creates a force on the electrons parallel to the wire, pushing electrons toward other end of the wire

microchip

small computer- not voltage source
communicate with switches and other external devices by apply voltage to pins connected to devices
low voltage. low current.

A 12 V battery is connected across the circuit shown. The resistance of bulb A is 200 Ω. When the switch is closed, the current through bulb A is 0.04 A. What is the voltage drop across bulb A?

8V

V=IR
(0.04)(200)

unit for current charge

coulomb (C)

unit for current

ampere (A)

equal to coulombs per second

electric current equation

I=Q/t

electric current= I
electric charge that passes through conductor= Q
time interval during which the charge flows = t

For a current of 0.20 A through a resistor, how many coulombs of charge pass through the resistor in 3 seconds?

0.60 C

Each amp represents one coulomb of charge per second; therefore 0.20 amp passes through the resistor each second. In 3 seconds, (0.20A)(3s)=0.60C(0.20A)(3s)=0.60C, or 600 millicoulombs (mC) pass through the resistor.

A student observes a wire carrying a constant current for an extended period of time. The student predicts that if the time the current flows increases, the total charge that passes a point in the wire will also increase. Which of the following explanations best justifies this prediction?
a) The charge increases because a constant current causes the electric field in the wire to grow stronger over time.
b) The charge increases because electrons move faster the longer the current flows.
c) The charge increases because current represents coulombs per second, so a longer time results in more total coulombs passing a point.
d) The charge on each electron increases as the current flows for a longer time.

c) The charge increases because current represents coulombs per second, so a longer time results in more total coulombs passing a point.

electrons orbiting atomic nuclei give each atom a…

magnetic field

permanent magnets

magnets with materials in which most molecules align with others forming a magnet with a north pole and a sout pole

if broken, each new piece have its own north and south pole