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The Rest of the Book

Page history last edited by Scott Pflaumer 10 months ago

Magnetism, Waves, Sound, Light, & Color Practice Problems

 

 

Magnetism

 

Magnets exert a Magnetic Force

Types of Magnets:

  • Magnetic poles exert magnetic force on each other.  

  • Permanent magnet: An object that can attract some objects and can also repel only like-poled permanent magnets. In a magnet, the magnetic domains are ordered but stuck in place. One way of knowing if an object is a magnet is by placing it near iron. If there is an interaction, then this object is a magnet because iron is not a magnet, but attracts magnets. In the image below the north pole is in the direction the arrows are pointing. The magnetic domains always have to stay in place facing one direction, which is why they always interact with other magnets and ferromagnets.

  • Ferromagnets: Objects that interact only with magnets, but not with each other or non-magnets. In a ferromagnet, the magnetic domains are random but can be ordered when brought near a permanent magnet. One way to test if an object is a ferromagnet is putting it near iron and a magnet. If there is an interaction with only the magnet, then the object is a ferromagnet. These domains can move around. This is why they don't interact with each other because the domains have no reason to switch direction. When placed next to a magnet, the domains all point in the same direction so that the ferromagnet will always attract the permanent. KEEP IN MIND: ferromagnets only attract permanent magnets, and do not repel.
  •  
  • Non-magnet: An object that does not interact with magnets or ferromagnets. In a non-magnet, the magnetic domains are all random and stuck in place. One way to see if an object is non-magnetic is by simply placing it near a magnet, if there is no interaction, it is non-magnetic. The domains are always stuck in place in random directions, similar to the start of the Ferromagnets.
  • Solenoid: When current is put through a coil of wire, the wire generates a magnetic field. Solenoids are made up of many loops of wire.
  •  


Magnet Interactions:

  • If 2 magnets repel, they must be permanent magnets.
  • Ferromagnets and magnets always attract.
  • 2 ferromagnets alone cannot interact.


Other Magnet Notes:

  • Magnetic domains: A specific are of the object, in which everything tends to line up (uniform magnetization).
  • To destroy a magnet, you can...

1. Heat it up.
2. Hit is really hard against something to mess up the magnetic domains.

  • A compass needle near a magnet may reverse polarity.
  • A pole of a strong magnet may attract both sides of a weaker magnet, but it will destroy the weaker magnet.
  • Large ferromagnetic objects that are left alone for a long time often develop north and south poles (over time, the magnetic domains align with the earth's magnetic field), and it can become a permanent magnet.
  • Permanent magnets have both south poles and north poles, similar to but not the same as positive and negative charges in the Electric Charge unit. If two north poles are held next to each other, they will repel. If a north and a south pole are held together, they will attract each other. -Because of this and historical ignorance, the north pole of Earth and the geographic north that is seen on a compass are two different things. While the technical north pole is in the direction known as south, the north pole we all know is actually the south pole. This is because if the magnet labeled north in a compass has a north polarity, then it will repel, not attract, to the north pole of Earth. Since we know that the magnet labeled north in a compass does have north polarity, it has to be attracting to Earth's south pole.


Every Magnet has a Magnetic Field that surrounds the object.

Practice Problem:
A student is observing how four objects react to each other. He labels them 1, 2, 3, and 4. He places R and B stickers on either end of each objects

He observes that:

  • Object 1 and object 3 don't interact
  • Object 2 and object 4 do not interact
  • The end of 2R and the end 3B attract
  • The end 1R and the end 2R attract

Classify the four objects and explain your reasoning.

Answer:
Object 1-ferromagnet
Object 2-permanent magnet
Object 3-ferromagnet
Object 4-non-magnet

Because objects 3 and 1 do not attract, but 1R and 2R attract and 2R and 3B attract, object 2 must be a permanent magnet. Object 1 and 3 are ferromagnets because they don't attract each other but they both attract the permanent magnet. Object 4 and 2 don't attract which means object 4 must be a non-magnet.

 

 

Waves and Oscillations

Waves vs. Oscillations
An oscillation is a motion in which an object moves, but with no total displacement. This means that it will move to various places, but always end the motion where it began.
A wave is a motion in which an object moves with a total displacement. Unlike oscillations, waves will move to different positions without ending in the initial starting point of motion.

Equilibrium Point: To calculate the equilibrium point of an oscillation, add the highest point and the lowest point, then divide the total by 2 (i.e.: If the highest point is 5m and the lowest point is 0m, then the equilibrium point would be 2.5m).

Similarities and Differences
Waves have displacement; Oscillations don't. Also, waves have speed and displacement.

Frequency: Cycle/Time
Period: Time/Cycle
Amplitude: Distance from equilibrium to farthest point on oscillation or wave.

λ (lambda): wavelength


Period vs. Frequency of an Object
An object's period is the amount of time is takes for it to complete 1 full cycle. -->Period=Time/Cycle
An object's frequency is the number of cycles that it completes in 1 second (or other given time). -->Frequency=Cycle/Time

Therefore, since an object's period and it's frequency are reciprocals of each other...
Period=1/Frequency
Frequency=1/Period


Wavelength is the distance the wave travels in one period. This measurement is normally found on a position vs position graph and you use the greek letter lambda to represent it.



Wave Speed
You find wave speed by taking wavelength and dividing it by period or a more simple formula is wavelength x frequency.

 

Sound Overview

 

As a part of the Sound unit which takes place at the end of the first or end of the second semester, we study the fascinating connection between physics and music which is explored through sound waves. 

   1. Through the sound lab, we explore the connections between sound waves and pitch. 

       a. The amplitude of sound is the volume

       b. The frequency of sound is the pitch 

       c. A human’s typical hearing is from 200-20,000 Hz. 

 

In instruments, there are: 

    a. Initial vibration

    b. Amplifier 

    c. And standing wave 

For a boomwhacker, for example, the amplifier is the whole tube, the initial vibration is the action of whacking the stick on a surface, and the standing wave is inside of the boomwhacker looking like this: the fixed ends are nodes and the free ends are antinodes. 

     a. In this case, the tube has two free ends and therefore has the wave pattern shown

In a tube where one end is fixed, the pattern now looks as follows: Compared to the first tube with two free ends, the tube with one fixed end is ¼ complete, which means it has a higher frequency. The other tube with two free ends had ½ the frequency. 

 

Fun exploration: How do noise cancelling headphones work? 

The headphones create a new wave which superimposes the sound wave through the headphones. In this way, the sound cancels each other out creating a noise-canceling experience. 

 

 

 

Digital vs. Analog Audio (review of sound/wave basics)

 

 

Color:

Paint:

  • Cyan, magenta, and yellow can be mixed to form a very wide range of colors
    • Called primary colors of pigment or paint
  • Secondary colors: 2 primary colors are mixed in certain proportions
  • Complementary colors: 2 colors are mixed in certain proportions to produce white or black
  • Early paints were made from natural materials
    • Shades of red can be made from iron oxides
  • Not all colors can occur readily in nature
  • Magenta, cyan, and yellow are primary colors, which are often confused with red, yellow, and blue. We do not consider red and blue to be primary colors because not all colors can be made from red and blue

 

Light

 

Practice Problems

1. Four metal bars are pictured below. Classify each of the bars as magnetic, ferromagnetic, or nonmagnetic.

  • End 2A and 3A attract
  • End 3A and 1B attract
  • Bar 2 and Bar 1 have no interaction
  • Bar 3 and Bar 4 have no interaction



2. Four metal bars are pictured below. Classify each of the bars as magnetic, ferromagnetic, or nonmagnetic. If magnetic, label the poles accordingly.

  • End 1A repels end 3B
  • Bar 3 attracts Bar 4
  • Bar 2 attracts Bar 1
  • Bar 4 and Bar 2 have no interaction



Solutions

1. Bar 1 - Ferromagnetic
Bar 2 - Ferromagnetic
Bar 3 - Magnetic
Bar 4 - Nonmagnetic
Explanation: Since one side of Bar 2 and Bar 3 attract, one of them must be a magnet. Also, one side of Bar 3 and Bar 1 attract, so one of them is a magnet. Bar 2 and Bar 1 have no interaction between each other, meaning that they must both be ferromagnetic. This is because they both were attracted to Bar 3, but not to each other. This also tells us Bar 3 must be a magnet. If Bar 4 has no interaction with Bar 3, it must be nonmagnetic because both magnets and ferromagnets interact with other magnets.


2. Bar 1 - Magnetic
Bar 2 - Ferromagnetic
Bar 3 - Magnetic
Bar 4 - Ferromagnetic
Explanation - Because Bar 1 and Bar 3 repel, and only magnets repel each other, they are both magnets. One side of Bar 1 and Bar 2 attract, so Bar 2 is either a magnet or a ferromagnet. One side of Bar 3 and Bar 4 attract, so Bar 4 is either a magnet or a ferromagnet. Since Bar 2 and Bar 4 have no interaction, they must both be ferromagnets.
Diagram showing poles (Note, the poles on each bar can be switched)

 

 

 

 

Phun Physics Facts

This page is meant to answer common questions and give interesting factoids regarding physics. It is designed for a better understanding of concepts and for those who are interested.

 

 

The Speaker Project

 

This project is a huge part of the Core Curriculum. It requires students to research, plan and build their own unique and creative speaker. It seems like a lot but don't worry!! Here are some tips for staying stress free and building an awesome speaker.

 

1) Be creative!! You won't get full credit if your speaker idea is to build a speaker for a singer. Put some effort into deciding on your user. Make it interesting!

 

2) Don't be overwhelmed with the complexities of how to make a speaker. Don't try to complicate the design either. Use the worksheet Mr. And is going to give to you, it gives a great simple explanation. But as for design, don't be afraid to do something creative, or eco-friendly, or revolutionary!

 

3) Don't get behind! There are many steps and assignments that go along with the speaker project and don't want to procrastinate. You will have lots of time in class, but use it wisely or you will be scrambling to get all the pieces together at the end. 

 

4) Don't give yourself too high of an expectation! You most likely will not end up creating a Bose Speaker, but that doesn't mean it's the end of the world. With the materials provided and the time given, you may only be able to create a small speaker that barely sounds like a whisper. during your presentation, stay positive about your speaker and don't knock yourself down.

 

5) Make a good presentation! This is a chance to show all that you've learned while creating a speaker, so make something cool, not a wordy PowerPoint. And don't forget to prepare and know what you're going to say. 

 

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