12 Weeks to TAKS

Week 5

• Obj. 5: IPC 5A and 5B Demonstrate wave types and their characteristics through a variety of activities such as modeling with ropes and coils, activating tuning forks and interpreting data on seismic waves. Demonstrate wave interactions including interference, polarization, reflection, refraction, and resonance within various materials.

• IPC 6F Investigate and compare series and parallel circuits.

WAVES

By moving a rope regularly up and down, a traveling or periodic wave is produced. Waves transfer energy from one place to by vibrating something up and down, or back and forth.

A transverse wave is a wave in which the particles of the medium are displaced in a direction perpendicular to the direction of energy transport.

. The crest of a wave is the point on the medium which exhibits the maximum amount of positive or upwards displacement from the rest position.

The trough of a wave is the point on the medium which exhibits the maximum amount of negative or downwards displacement from the rest position

The amplitude of a wave refers to the maximum amount of displacement of a a particle on the medium from its rest position. The amount of energy carried by a wave is related to the amplitude of the wave.

A longitudinal wave is a wave in which the particles of the medium are displaced in a direction parallel to the direction of energy transport.

• A compression is a point on a medium through which a longitudinal wave is traveling which has the maximum density. A region where the coils are spread apart, thus maximizing the distance between coils, is known as a rarefaction. A rarefaction is a point on a medium through which a longitudinal wave is traveling which has the minimum density.

A tuning fork serves as a useful illustration of how a vibrating object can produce sound.

Characteristics of Waves: a. Frequency – the number of complete waves passing a point in space per second; depends on the source b. Wavelength – the distance from a point in a wave to the next point that wave in the same phase, often symbolized with (lambda)

By knowing the frequency of a wave and its wavelength, we can find its velocity. Here is the equation for the velocity of a wave:

velocity = wavelength x frequency or

v = x f

• Light waves will always travel in a straight line until they hit a barrier. So whether its traveling through air, water, glass, diamond, or any substance (or none at all), light travels in a straight path, until it encounters a different medium.

All visible objects either emit light or reflect light. When an object either emits light or reflects it, the light travels in all directions from the object. If viewed through a

pinhole the light rays encounter no different medium so they travel in a straight line.

Wave Properties: Reflection When a wave hits a

barrier, it will be reflected depending on the direction of the barrier (normal). The angle between the incident wave and the normal is the same as the angle between the normal and the reflected wave. 

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• Reflections are commonly observed with sound waves. Echos are reflected sound waves. When you yell in a canyon, the sound wave travels through the medium (air in this case), reflects off the canyon wall and returns to its origin (you). The result is that you hear the echo (the reflected sound wave) of your original yell.

Wave Properties: Refraction When a wave enters a different medium (more shallow region) at an angle, the direction of waves changes. This change is called refraction. The energy transferred depends on the difference between the mediums. If there is a significant difference, almost all the energy will be reflected. If the mediums are similar, most of the energy will be transferred.

• Refraction causes objects to appear in a different place than it actually is because when light passes into a different medium the light path bends.

Wave Properties: InterferenceWhen two waves traveling in opposite directions through the same medium collide, the amplitude of the resulting wave will be the sum of the two initial waves. This is called interference and there are of two types:

1. Constructive interference is when the amplitudes of the initial waves are in the same direction. The resulting wave will be larger than the original waves.

2. Destructive interference is when the amplitudes of the initial waves are opposite. The amplitude of the resulting wave will be zero.

Wave Properties: Polarizaton• A light wave which is vibrating in more

than one plane is referred to as unpolarized light. Polarized light waves are light waves in which the vibrations occur in a single plane. The process of transforming unpolarized light into polarized light is known as polarization.

Wave Properties: Resonance• Resonance causes an object to

move back and forth or up and down.

For resonance to occur three things must be present.

• A) An Object With a Natural Frequency. • B) A Second Object that Can Oscillate at

the Same Frequency as the Natural Frequency: Energy is transferred by a wave from a vibrating object to a second object.

• C) A Lack of Energy Loss: For an object to resonate energy has to build up in the object.

Electricity

Electricity generally refers to the flow of electrons.

Types of Electricity

• Static Electricity - no motion of free charges

• Current Electricity - motion of free charges– Direct Current (DC)– Alternating Current (AC)

Electrical CircuitsA circuit is a loop of wire with its ends connected to an energy source such as a battery. One end of the wire is connected to the positive terminal; the other end of the wire is connected to the negative terminal. The wire is connected in this way so a current can flow through it.

Resistors can be connected in series; that is, the current flows through them one after another.

Series Circuits

Parallel CircuitsA parallel circuit is rather like two or more series circuits connected to the same energy source. For example, here is a parallel circuit connecting a battery and three resistors.

• Series circuits have two disadvantages when compared with parallel circuits. The first disadvantage is that, if one component in a series circuit fails, then all the components in the circuit fail because the circuit has been broken. The second disadvantage is that the more components there are in a series circuit, the greater the circuit's resistance.

Parallel circuits have two advantages whencompared with series circuits. • The first advantage of a parallel circuit is that a

failure of one component does not lead to the failure of the other components. This is because a parallel circuit consists of more than one loop and has to fail in more than one place before the other components fail.

• The second advantage of parallel circuits is that more components may be added in parallel without the need for more voltage.

Ohm’s Law• Ohm's Law deals with the relationship

between voltage and current in an ideal conductor.

• Ohm's Law is given by:

•V = I R

V R

I

Voltage

• Voltage (V) can be thought of as the force pushing electric charges along a conductor

Resistance

• Resistance (R) is a measure of how difficult it is to push the charges along.

Current

• Electric current (I) is the movement of electric charge in a conductor.