Biophysics


Reaction Time
  1. Get a meter stick.  You will be testing peoples' reaction time under various conditions.
  2. You will test how quick peoples' reactions are 1) when you tell them that you will be dropping the meter stick, 2) when you don't tell them when you are dropping the meter stick, and 3) when you tell them that you will be dropping the stick, but their eyes are closed.  Come up with a fourth experiment and write it down.
  3. Find three people to test.  These people should not be in your group.  Write down their names.
  4. You will test people by having them hold their hands three inches apart where the meter stick reads "0".  You will hold it so that "100" is above their hands.  On your signal, you will drop and they will grab the meter stick.  Their reaction time is measured by where they grab the meter stick.
  5. For each person, do each test at least three times.
  6. After you are finished collecting data, find the average reaction time for each person for each test.
  7. Make a table to represent the data.
  8. Which test showed the quickest reaction times?
  9. Which test showed the slowest reaction times?
  10. Which people had the quickest reactions?
  11. Which people had the slowest reactions?
  12. Identify at least three patterns that you can see in the data.  What do these conclusions tell you about the human nervous system?
Nervous System Introduction
  1. Using the biology book, identify the different parts and roles of the brain.
  2. Watch the “Discovery: How Neurons Work” video on teachertube.com . Answer the following questions:
    1. What does the cortex do?
    2. What do neurons do?
    3. How do messages get passed from one neuron to the next?
    4. How many neurons are in the brain? How many connections?
  3. On the computers, visit the following web sites and complete the questions:
Kanizsa Triangle: http://123opticalillusions.com/pages/skanizsa_triangle.gif
  1. Describe what you see.
  2. Our brain perceives certain things that our eyes are not seeing. What evolutionary reason do you think there would be to see a particular shape where there is no shape?
Color Blindness: http://www.colorcube.com/illusions/clrblnd.htm
  1. Do the test. What were your results?
  2. What does this tell you about how our eyes see color?
Reverse U.S. Flag: http://photos1.blogger.com/photoInclude/blogger/5639/2020/1600/usa-flag.0.jpg
  1. Stare at the dot in the middle of the flag for 30 seconds, then stare at a white sheet of paper or at a white wall. What do you see?
  2. This is called an “afterimage” effect. Why do you think that this happens?
  1. Using the biology book, identify the different parts and roles of the brain.
  2. Watch the “Discovery: How Neurons Work” video on teachertube.com . Answer the following questions:
    1. What does the cortex do?
    2. What do neurons do?
    3. How do messages get passed from one neuron to the next?
    4. How many neurons are in the brain? How many connections?
  3. On the computers, visit the following web sites and complete the questions:
Kanizsa Triangle: http://123opticalillusions.com/pages/skanizsa_triangle.gif
  1. Describe what you see.
  2. Our brain perceives certain things that our eyes are not seeing. What evolutionary reason do you think there would be to see a particular shape where there is no shape?
Color Blindness: http://www.colorcube.com/illusions/clrblnd.htm
  1. Do the test. What were your results?
  2. What does this tell you about how our eyes see color?
Reverse U.S. Flag: http://photos1.blogger.com/photoInclude/blogger/5639/2020/1600/usa-flag.0.jpg
  1. Stare at the dot in the middle of the flag for 30 seconds, then stare at a white sheet of paper or at a white wall. What do you see?
  2. This is called an “afterimage” effect. Why do you think that this happens?
Senses: Vision
Calculations
One of the most dramatic experiments to perform is the demonstration of the blind spot. The blind spot is the area on the retina without receptors that respond to light. Therefore an image that falls on this region will NOT be seen. It is in this region that the optic nerve exits the eye on its way to the brain. To find your blind spot, look at the image below or draw it on a piece of paper:
o                                  +
To draw the blind spot tester on a piece of paper, make a small dot on the left side separated by about 6-8 inches from a small + on the right side. Close your right eye. Hold the image (or place your head from the computer monitor) about 20 inches away. With your left eye, look at the +. Slowly bring the image (or move your head) closer while looking at the +. At a certain distance, the dot will disappear from sight...this is when the dot falls on the blind spot of your retina. Reverse the process. Close your left eye and look at the dot with your right eye. Move the image slowly closer to you and the + should disappear.
Here are some more images that will help you find your blind spot. For this image, close your right eye. With your left eye, look at the red circle. Slowly move your head closer to the image. At a certain distance, the blue line will not look broken!! This is because your brain is "filling in" the missing information.This next image allows you to see another way your brain fills in the blind spot. Again, close your right eye. With your left eye, look at the +. Slowly move your head closer to the image. The space in the middle of the vertical lines will disappear. In the next two images, again close your right eye. With your left eye, look at the numbers on the right side, starting with the number "1." You should be able to see the "sad face" (top image) or the gap in the blue line (bottom image) in your peripheral vision. Keep your head still, and with your left eye, look at the other numbers. The sad face should disappear when you get to "4" and reappear at about "7." Similarly the blue line will appear complete between "4" and "7." Here is another image to show your blind spot. Close your right eye. With your left eye, look at the +. You should see the red dot in your peripheral vision. Keep looking at the + with your left eye. The red dot will move from the left to the right and disappear and reappear as the dot moves into and out of your blind spot.
The blind spot is caused when light falls on an area of the retina without photoreceptors. How big is this area on the retina? Here is one way to find out the horizontal diameter of the blind spot. 
    1. Make a tester by marking + on the far right side of a piece of notebook paper.
  • Stand with your back to a wall, with your head touching the wall.
  • Hold the tester 500 mm (0.5 m or 50 cm) in front of your eye. (It may help to have someone help you.)
  • Close your right eye and look at the + with your left eye.
  • Place a pencil eraser on the far left side of the tester.
  • Slowly move the pencil eraser to the right.
  • When the eraser disappears, mark this location on the tester. Call this point "A."
  • Continue moving the eraser to the right until it reappears. Mark this location on the tester. Call this point "B."
  • Repeat the measurements until you are confident that they are accurate.
  • Measure the distance between the spots where the eraser disappeared and reappeared.
  To calculate the width of your blind spot on your retina, let's assume that 1) the back of your eye is flat and 2) the distance from the lens of your eye to the retina is 17 mm. We will ignore the distance from the cornea to the lens.   With the simple geometry of similar triangles, we can calculate the size of the blind spot because triangle ABC is similar to triangle CDE. So, the proportions of the lines will be similar.   When I did this experiment, the measured distance between point A and point B was 46 mm. Inserting 46 mm into the equation, the blind spot on my retina has a diameter of 1.56 mm.   <table border=1 bgcolor="#ffffff" cellspacing =5
Set up Example
Senses: Touch
  1. Choose a data recorder, a subject, and a tester for your group.
  2. Find the Data Recording Sheet at the end of this Student Guide and begin the experiment with the first skin area on the list, the forehead.
  3. The subject must either close his/her eyes or wear a blindfold. (The subject may not watch the procedure—this would give away the answer!)
  4. The tester should use a cork with two toothpicks (or pins) stuck into it. You can use one cork and move the toothpicks different distances apart, or use several corks, each one with two toothpicks a measured distance apart. Your teacher will give further instructions on how to do this.
  5. The tester should start with toothpicks about 50millimeters (mm) apart. Make sure that the two points touch the skin at the same time.
  6. The data recorder asks how many points the subjects feels. If the person feels two, move the points closer together — about 40 mm apart, and check again.
  7. Continue the procedure until you find the smallest distance the points can be separated for the person to feel two points instead of one. When the person reports “one point” for the first time, move the two points apart only one or two millimeters at a time and try to make a very accurate measurement.
  8. When the smallest distance is found, the data recorder can measure the distance in millimeters between the two points while the experimenter holds them on the subject.
  9. Continue this process for the rest of the skin areas on the Data Sheet.
  10. Use fresh toothpicks if another person becomes a subject.
DATA AND OBSERVATIONS
  1. After you have measured and recorded all distances on the Data Sheet, make a histogram of your results on the graph provided at the end of the Student Guide.
  2. Write down any other interesting things you noticed while doing this experiment.
ANALYSIS: THINK ABOUT IT!
  1. How do your results compare with those of other groups?
  2. Are the two-point distances on different areas of the skin the same—for example, is the measurement on fingertips the same as the measurement on the back of the leg?
  3. Which parts of the body are best at telling that two points are touching them even when the points are very close together?
  4. Which skin areas do you think have more receptors, areas that have small two-point distances, or large two-point distances? Why do you think so?
  5. Which brain area do you think is larger, one receiving information from skin with lots of receptors, or from skin with a few receptors?
  6. How does information from sensory receptors in the skin get to the brain?
CONCLUSIONS
  1. List three findings you think are important from today’s experiment. Were you surprised by anything you found?
  2. How could you improve this experiment?
DATA RECORDING SHEET
SKIN AREA FOR TESTING MINIMUM DISTANCE FOR TWO POINT DISCRIMINATION in millimeters (mm)
FOREHEAD
CHEEK
FOREARM
PALM OF HAND
TIP OF THUMB
TIP OF INDEX FINGER
BACK OF LOWER LEG
Muscular System: Identification

Label the above figures using the information below:

Your trapezius extends your head and neck, which is found next to the deltoid muscles that raise your arms.  Another muscle that controls your arms, the pectoralis major (or "pecs") pulls your arms in front of your body.  On your arm itself, there is the upper and lower half.  The upper arm has your biceps and triceps; the biceps contract your arm and your triceps, located on the bottom of your upper arm, extend your arm outwards.  The lower arm, or forearm, has two muscles that control how your wrist rotates.  The brachioradialis is located on the front of your body and the supinator is on the back of your body.

Your torso contains several very large muscles that control how your upper body moves.  The latissimus dorsi (or "lats") control your arm movements away from your body and rotating in place.  They are the largest muscles in your back.  The rectus abdominus (or "abs") contracts your entire torso, such as when you do sit-ups or crunches.  The external oblique muscles, on the sides of your torso, allow you to rotate your torso like you're turning to talk to someone.

Finally, your legs!  Let's start with the most famous and admired muscles, the gluteus maximus (or "glutes").  They are your "butt" muscles and extend your entire leg.  The quadriceps (located on top of your thighs) extend your lower leg and the biceps femoris help to contract your lower leg.  The tibialis anterior raises your foot upwards while the gastrocnemius on the back of your lower leg extends your foot downwards.  Lastly, the soleus is located near your ankle and is critical to running, walking and dancing!

F1 & B1 - Trapezius

F2 & B2 - Deltoid

F3 - Pectoralis Major ("Pecs")

B3 - Triceps

F4 - Biceps

B4 - Latissimus Dorsi ("Lats")

F5 - Rectus Abdominus ("Abs")

B5 & F6 - External Oblique

B6 - Supinator

F7 - Brachioradialis

B7 - Gluteus Maximus ("Glutes")

F8 - Quadriceps

B8 - Biceps Femoris

F9 - Tibialis Anterior

B9 - Gastrocnemius

B10 - Soleus

Muscular System: Movement
  1. When you bend your arm at your elbow, your biceps are flexing and your triceps are extending. Is the following statement is true: Most people's biceps are stronger than their triceps?
  2. You will perform an experiment to test this statement, with a 1kg weight.  Group members will take turns doing the following exercise: Standing with your back against a wall, hold the weight in your dominant hand, letting the weight hang at your side with your arm fully extended downward. Raise the weight by bending your arm from the elbow toward your face as far as you can. Lower the weight by fully extending the arm downward.
  3. Repeat the exercise until you feel tired. Record the number of repetitions for each student.
  4. Standing with your back against a wall, hold the weight in your dominant hand, letting the weight hang at your side with your arm fully extended downward. Bend your arm at the elbow, bringing the weight up toward your face and holding the weight next to your ear on the same side of the body. Rotate your wrist so your palm is facing away from you. Now push the weight straight up into the air until the arm is fully extended; then return the weight so that it is next to your ear again.
  5. Repeat the exercise until you feel tired. Group members should record the number of repetitions for each student.
  6. Compute class averages for the "flex" and "extend" exercises.
  7. Did the results of the test agreed with the vote prior to the experiment?  Why or why not?
  8. What makes one muscle stronger than another?
  9. Come up with exercises to train the following pairs of muscles:
Deltoids vs. Pectoralis Major Supinator vs. Brachioradialis Tibialis Anterior vs. Gastrocnemius Quadriceps vs. Biceps femoris
Skeleton Identification
Identify the bones in the body from the following passage. Let's start at the base of the skeleton, the spinal column.  Your spinal, or vertebral, column, is the place in your skeleton where the rest of the skeleton branches off.  At the top of the backbone, the cervical vertebrae connect the skull to the spinal column.  Separate from the skull, the mandible forms your lower jaw. The thoracic vertebrae can be found directly below the cervical vertebrae, where the ribs branch off.  The sternum connects the ribs together in the "breastbone".  Connected to the top of the sternum are the two clavicles which you can feel between your shoulders and breastbone.  Those clavicles then form a joint with the scapula and humerus.  Your scapula is your shoulder bone, and the humerus is upper arm.  Your lower arm is composed of two bones, the radius and ulna.  The radius is on the thumb side, while the ulna is on the pinky side of the forearm.  Lastly, we get to your hands.  Your wrist is made up of carpals, the inner hand is made up of metacarpals, and your fingers (just like your toes) are phalanges. Below the cervical and thoracic vertebrae, the lumbar vertebrae act as the major support structure for your abdominal section.  Continuing down the spinal column, the sacrum is found opposite the innominate (or pelvic) bone which forms the structure to your hips.  From the innominate bone comes your legs, starting with the femur.  The knee is made up of a floating bone called the patella, and then your lower leg is made up of two bones (just like your lower arm).  The tibia is on the big toe side of your leg and is much bigger than your fibula.  Just like in your hand, the ankle is made up tarsals, the inner foot is made up of metatarsals, and the toes are phalanges. The final part of the spinal column is the tailbone, or coccyx.
Broken Bones
The skeletal system is responsible for creating cells that help keep us healthy (white blood cells), protects our vital organs and supports our muscular system, allowing us to move.  In order for bones to maintain themselves, they must constantly break down and rebuild the collagen and minerals that they are made of. Cells called osteoclasts are multinucleated cells that eat away the bone's mineral coating and collagen. You can think of them as "bone destroyers."  Cells called osteoblasts are cells that lay new collagen and coat the bone with fresh minerals. You can think of them as "bone creators."  The process of bone destruction and creation is never ending. As a result of this constant breakdown and replacement, human bones are never more than 20 years old. When a bone is broken:
  • The injury is flooded with natural painkillers called endorphins, which temporarily block out pain.
  • An injury will swell because the body is sending extra oxygen and nutrients to the injury to begin the healing process.
  • A large hematoma, which is a collection of blood, surrounds the break in the bone.
  • Stem cells, which are responsible for making new cells, usually divide every one to two days. Now that there is an injury, they will divide every three minutes.
  • Within four weeks the hematoma will harden around the break, making the injured area extra strong.
  • Over the next several months, osteoclasts will "eat away" the hardened hematoma and the injury will be repaired.
  • Within a year of the injury, the bone will be almost as strong as it was before the break!
Draw (in cartoon style) the process of bone repair following a break, making sure to incorporate at least five vocabulary words you have learned. You can use the following diagrams to help:

Levers
  Read the information to fill in the following blanks:
  1. A lever is a simple machine that makes _______________ easier; it involves moving a _______________ around a pivot called a fulcrum using a force. Many of our basic tools use levers.
  2. In a Type 1 [1st class] Lever, the _________________ is between the effort and the load. In an off-center type one lever (like a pliers), the load is larger than the effort, but is moved through a smaller_____________.
  3. Three examples of common tools (and other items) that use a type 1 [1st class] lever include:
  4. In a Type 2 [2nd class] Lever, the ________________is between the pivot (fulcrum) and the effort.
  5. Three examples of 2nd class levers are:
  6. In a Type 3 [3rd class] Lever, the ____________________is between the pivot (fulcrum) and the load.
  7. Three examples of 3rd class levers are:
Levers are one of the basic tools that were probably used in prehistoric times. Levers were first described about 260 BC by the ancient Greek mathematician Archimedes (287-212 BC). A lever is a simple machine that makes work easier for use; it involves moving a load around a pivot using a force. Many of our basic tools use levers, including scissors (2 class 1 levers), pliers (2 class 1 levers), hammer claws (a single class 2 lever), nut crackers (2 class 2 levers), and tongs (2 class 3 levers).
A Type 1 Lever. A Type 2 Lever. A Type 3 Lever.
Type 3 Lever In a Type 1 Lever, the pivot (fulcrum) is between the effort and the load. In an off-center type one lever (like a pliers), the load is larger than the effort, but is moved through a smaller distance. Examples of common tools (and other items) that use a type 1 lever include:
Item Number of Class 1 Levers Used
see-saw a single class 1 lever
hammer's claws a single class 1 lever
scissors scissors 2 class 1 levers
pliers pliers 2 class 1 levers
Type 2 Lever In a Type 2 Lever, the load is between the pivot (fulcrum) and the effort. Examples of common toolsthat use a type 2 lever include:
Item Number of Class 2 Levers Used
stapler a single class 2 lever
bottle opener a single class 2 lever
wheelbarrow a single class 2 lever
nail clippers Two class 2 levers
nut cracker Two class 2 levers
Type 2 Lever In a Type 3 Lever, the effort is between the pivot (fulcrum) and the load. Examples of common tools that use a type 3 lever include:
Item Number of Class 3 Levers Used
fishing rod a single class 3 lever
tweezers Two class 3 levers
tongs Two class 3 levers
  1. Levers are an essential part of many mechanisms. They can be used to change the___________, the ____________ and the _______________ of movement.
  2. The fixed point of the lever about which it moves is known as the_________________.
  3. In the example on the webpage, the force and the load move in opposite directions. With the force three times closer to the fulcrum them the load lifted is only one ____________ of the force but it move three times as______________.
  4. First order lever. Like a see-saw or balance, the _____________ and the ______________ are separated by the fulcrum. As one moves up the other moves____________________. The amount and the strength of the movement are proportional to the __________________from the fulcrum.
  5. Second order lever. A wheel barrow is a second order lever. Here the load is between the _______________and the fulcrum. This uses mechanical advantage to ease lifting of a large weight.
  6. Third order lever. Here the _______________ is between the fulcrum and the load. Mechanical advantage is reduced but the movement at the load point is increased.
  7. Draw and label a diagram of each of the 3 types of levers: 1st Class, 2nd Class, 3rd Class
Levers are an essential part of many mechanisms. They can be used to change the amount, the strength and the direction of movement.  The position of the force and the load are interchangeable and by moving them to different points on the lever, different effects can be produced. The fixed point of the lever about which it moves is known as the fulcrum. In this example the force and the load move in opposite directions. With the force three times closer to the fulcrum them the load lifted is only one third of the force but it move three times as far. First order lever. Like a see-saw or balance, the load and the force are separated by the fulcrum. As one moves up the other moves down. The amount and the strength of the movement is proportional to the distance from the fulcrum. Second order lever.A wheel barrow is a second order lever. Here the load is between the force and the fulcrum.  This uses mechanical advantage to ease lifting of a large weight. Third order lever. Here the force is between the fulcrum and the load. Mechanical advantage is reduced but the movement at the load point is increased. Procedure: From the available materials, make three lever systems (one of each order) and answer these questions for each: 1. How much force (n) does it take to lift (move) the load? 2. Can you lift (move) a load using only one finger? 3. Does it always take the same amount of force to lift (move) the load? 4. Where should you apply effort to lift (move) a load with the least amount of force? 5. How does the amount of force needed to lift (move) a load change when the type of lever system changes?
Electricity
What is Electricity? Electricity is a naturally occurring force that exists all around us.  Humans have been aware of this force for many centuries. Ancient man believed that electricity was some form of magic because they did not understand it. Greek philosophers noticed that when a piece of amber was rubbed with cloth, it would attract pieces of straw. They recorded the first references to electrical effects, such as static electricity and lightning, over 2,500 years ago. It was not until 1600 that a man named Dr. William Gilbert coined the term “electrica,” a Latin word which describes the static charge that develops when certain materials are rubbed against amber. This is probably the source of the word “electricity." Electricity and magnetism are natural forces that are very closely related to one another. You will learn a little about magnetism in this section, but there is a whole section on magnetism if you want to learn more. In order to really understand electricity, we need to look closely at the very small components that compose all matter. Electrons Electrons are the smallest and lightest of the particles in an atom. Electrons are in constant motion as they circle around the nucleus of that atom. Electrons are said to have a negative charge, which means that they seem to be surrounded by a kind of invisible force field. This is called an electrostatic field. Protons Protons are much larger and heavier than electrons. Protons have a positive electrical charge. This positively charged electrostatic field is exactly the same strength as the electrostatic field in an electron, but it is opposite in polarity. Notice the negative electron (pictured at the top left) and the positive proton (pictured at the right) have the same number of force field lines in each of the diagrams. In other words, the proton is exactly as positive as the electron is negative. Like charges repel, unlike charges attract Two electrons will tend to repel each other because both have a negative electrical charge. Two protons will also tend to repel each other because they both have a positive charge. On the other hand, electrons and protons will be attracted to each other because of their unlike charges. Since the electron is much smaller and lighter than a proton, when they are attracted to each other due to their unlike charges, the electron usually does most of the moving. This is because the protons have more mass and are harder to get moving. Although electrons are very small, their negative electrical charges are still quite strong. Remember, the negative charge of an electron is the same as the positive electrical charge of the much larger in size proton. This way the atom stays electrically balanced. Another important fact about the electrical charges of protons and electrons is that the farther away they are from each other, the less force their electric fields have on each other. Similarly, the closer they are to each other, the more force they will experience from each other due to this invisible force field called an electric field. Maintaining electrical balance Each basic element has a certain number of electrons and protons, which distinguishes each element from all other basic elements. In most elements, the number of electrons is equal to the number of protons. This maintains an electrical balance in the structure of atoms since protons and electrons have equal, but opposite electrostatic fields. Pictured here is an atom of copper, which is much more complex than either an atom of hydrogen or helium. The copper atom has 29 protons in its nucleus with 29 electrons orbiting the nucleus. Notice that in the copper atom, the electrons are arranged in several layers called shells. This is to graphically represent that the electrons are at different energy levels within the atom. The energy of an electron is restricted to a few particular energy levels. The energy is said to be quantized, meaning that it cannot vary continuously over a range, but instead is limited to certain values. These energy levels or shells follow a very predictable pattern. The closest shell to the nucleus can have up to 2 electrons. The second shell from the nucleus can have up to 8 electrons. The third shell can have up to 18 electrons. The fourth shell can have up to 32 electrons, and so on. Atoms can have this many electrons, but they do not have to have this many electrons in each shell. The greater distance between the electrons in the outer shells and the protons in the nucleus mean the outer shell electrons experience less of a force of attraction to the nucleus than do the electron in the inner shells. What is the valence shell? Notice that in the copper atom pictured below that the outside shell has only one electron. This represents that the copper atom has one electron that is near the outer portion of the atom. The outer shell of any atom is called thevalence shell. When the valence electron in any atom gains sufficient energy from some outside force, it can break away from the parent atom and become what is called a free electron. Pictured here is an atom of copper, which is much more complex than either an atom of hydrogen or helium. Atoms with few electrons in their valence shell tend to have more free electrons since these valence electrons are more loosely bound to the nucleus. In some materials like copper, the electrons are so loosely held by the atom and so close to the neighboring atoms that it is difficult to determine which electron belongs to which atom. Under these conditions, the valence or free electrons tend to drift randomly from one atom to its neighboring atoms. Under normal conditions the movement of the electrons is truly random, meaning they are moving in all directions by the same amount. However, if some outside force acts upon the material, this flow of electrons can be directed through materials and this flow is called electrical current. Materials that have free electrons and allow electrical current to flow easily are called conductors. Many materials do not have any free electrons. Because of this fact, they do not tend to share their electrons very easily and do not make good conductors of electrical currents. These materials are called insulators. There will be more information on this later. Electricity is a term used to describe the energy produced (usually to perform work) when electrons are caused to directional (not randomly) flow from atom to atom. In fact, the day-to-day products that we all benefit from, rely on the movement of electrons. This movement of electrons between atoms is called electrical current. We will look at how electrical current is produced and measured in the following pages. It is very important to have a way to measure and quantify the flow of electrical current. When current flow is controlled it can be used to do useful work. Electricity can be very dangerous and it is important to know something about it in order to work with it safely. The flow of electrons is measured in units called amperes. The term amps is often used for short. An amp is the amount of electrical current that exists when a number of electrons, having one coulomb (ku`-lum) of charge, move past a given point in one second. A coulomb is the charge carried by 6.25 x 10^18 electrons. 6.25 x 10^18 is scientific notation for 6,250,000,000,000,000,000. That is a lot of electrons moving past a given point in one second! Since we cannot count this fast and we cannot even see the electrons, we need an instrument to measure the flow of electrons. An ammeter is this instrument and it is used to indicate how many amps of current are flowing in an electrical circuit. We also need to know something about the force that causes the electrons to move in an electrical circuit. This force is called electromotive force, or EMF. Sometimes it is convenient to think of EMF as electrical pressure. In other words, it is the force that makes electrons move in a certain direction within a conductor. But how do we create this “electrical pressure” to generate electron flow? There are many sources of EMF. Some of the more common ones are: batteries, generators, and photovoltaic cells, just to name a few. Batteries are constructed so there are too many electrons in one material and not enough in another material. The electrons want to balance the electrostatic charge by moving from the material with the excess electrons to the material with the shortage of electrons. However, they cannot because there is no conductive path for them to travel. However, if these two unbalanced materials within the battery are connected together with a conductor, electrical current will flow as the electron moves from the negatively charged area to the positively charged area. When you use a battery, you are allowing electrons to flow from one end of the battery through a conductor and something like a light bulb to the other end of the battery. The battery will work until there is a balance of electrons at both ends of the battery. Caution: you should never connect a conductor to the two ends of a battery without making the electrons pass through something like a light bulb which slows the flow of currents. If the electrons are allowed to flow too fast the conductor will become very hot, and it and the battery may be damaged. We will discuss how electrical generators use magnetism to create EMF in a coming section. Photovoltaic cells turn light energy from sources like the sun into energy. To understand the photovoltaic process you need to know about semiconductors so we will not cover them in this material. How does the amp and the volt work together in electricity? To understand how voltage and amperage are related, it is sometimes useful to make an analogy with water. Look at the picture here of water flowing in a garden hose. Think of electricity flowing in a wire in the same way as the water flowing in the hose. The voltage causing the electrical current to flow in the wire can be considered the water pressure at the faucet, which causes the water to flow. If we were to increase the pressure at the hydrant, more water would flow in the hose. Similarly, if we increase electrical pressure or voltage, more electrons would flow in the wire. Does it also make sense that if we were to remove the pressure from the hydrant by turning it off, the water would stop flowing? The same is true with an electrical circuit. If we remove the voltage source, or EMF, no current will flow in the wires. Another way of saying this is: without EMF, there will be no current. Also, we could say that the free electrons of the atoms move in random directions unless they are pushed or pulled in one direction by an outside force, which we call electromotive force, or EMF. There is another important property that can be measured in electrical systems. This is resistance, which is measured in units called ohms. Resistance is a term that describes the forces that oppose the flow of electron current in a conductor. All materials naturally contain some resistance to the flow of electron current. We have not found a way to make conductors that do not have some resistance. If we use our water analogy to help picture resistance, think of a hose that is partially plugged with sand. The sand will slow the flow of water in the hose. We can say that the plugged hose has more resistance to water flow than does an unplugged hose. If we want to get more water out of the hose, we would need to turn up the water pressure at the hydrant. The same is true with electricity. Materials with low resistance let electricity flow easily. Materials with higher resistance require more voltage (EMF) to make the electricity flow. The scientific definition of one ohm is the amount of electrical resistance that exists in an electrical circuit when one amp of current is flowing with one volt being applied to the circuit. Is resistance good or bad? Resistance can be both good and bad. If we are trying to transmit electricity from one place to another through a conductor, resistance is undesirable in the conductor. Resistance causes some of the electrical energy to turn into heat so some electrical energy is lost along the way. However, it is resistance that allows us to use electricity for heat and light. The heat that is generated from electric heaters or the light that we get from light bulbs is due to resistance. In a light bulb, the electricity flowing through the filament, or the tiny wires inside the bulb, cause them to glow white hot. If all the oxygen were not removed from inside the bulb, the wires would burn up. An important point to mention here is that the resistance is higher in smaller wires. Therefore, if the voltage or EMF is high, too much current will follow through small wires and make them hot. In some cases hot enough to cause a fire or even explode. Therefore, it is sometimes useful to add components called resistors into an electrical circuit to restrict the flow of electricity and protect the components in the circuit. Resistance is also good because it gives us a way to shield ourselves from the harmful energy of electricity.
  1. Define electricity and identify the origins of the term.
  2. Discuss how electricity can be observed in the world.
  3. Explain the differences between electrons and protons.
  4. Predict what happens when protons and electrons interact with other protons or electrons.
  5. Explain how electrons are arranged in an atom.
  6. Describe how elements maintain their electrical balance.
  7. Explain what free electrons are and why they are important.
  8. Explain how an electrical current is produced.
  9. Define amperes and name the instrument that is used to measures amperage.
  10. Construct an experiment to determine the amount of amps flowing in a circuit.
  11. Define EMF and explain how it is measured.
  12. Explain why EMF is important to the flow of electrical current.
  13. List several examples of sources of electromotive force.
  14. Define resistance and how we measure it.
  15. Discuss the similarities between resistance in a wire and the resistance in a water hose.
  16. Use the Build Your Own Battery Kit to build a battery!
  17. Perform the following lab.
Materials Needed: A typical kit for three students working as a group would consist of 2 batteries, 4 bulbs, 4 sockets, 12 pieces of wire (about 8 inches long and stripped at each end), 2 knife switches, 1 buzzer and 1 motor. Strategy: Describe and illustrate the flow of electrical current from the battery, through the wires and through a bulb. Construct a simple circuit using a single bulb: This can be followed by the introduction of a switch into the circuit to show how the light can be turned on and off. The next step is to make parallel circuits where the electrical surrent from the battery flows with equal voltage into two or more bulbs. After you have hooked up this circuit, you can then hook up a series circuit where the electrical current from the battery flows first through one bulb and then through the other. You can then loosen various bulbs in their sockets to show that a bulb will remain lit in a parallel circuit even though another bulb may be out. This can be compared to the series circuit where the loosening of one bulb in the circuit will cause any other bulb in the circuit to go out also. A further step would be the hook up of a parallel circuit using different components such as bulbs, buzzers and motors. Performance Assessment: You are graded based on two factors: 1. The ability to construct the circuits accurately and have them work properly. 2. The ability to explain the circuits by tracing the flow of current from the battery through the various elements of the circuit.
Final Project: Biophysics
For your final project, you will be working with Dr. Watson on a variety of labs and other activities. More information to follow!