ENERGY, WAVES, and ELECTRICITY UNIT REVIEW

Unit 4 Final Exam Review

What do the following units measure?

· S

Time

· m/sSpeed

· m/s2Acceleration

· m

Distance

· NForce

· JEnergy

· W Power

WAVES:

1. Describe a wave in terms of wavelength, amplitude, frequency and speed.

a. Wavelength is the length of one wave (distance from crest to crest, trough to trough etc.) amplitude is half the total height of the wave, frequency is the number of waves per second and speed is the distance a wave travels per second.

2. What are examples of transverse and longitudinal waves?

a. Transverse: ocean waves, wave at a sporting event

b. Longitudinal: sound waves

3. Compare and contrast transverse and longitudinal waves.

a. Both transfer energy from one point to another, however transverse transport energy perpendicular to the particle vibration and longitudinal transfer parallel to the particle vibration.

4. What are 3 examples of energy being transferred through waves? What is the source of vibration for each wave?

a. Sunlight reaching Earth (infrared radiation), sound wave carrying a sound (sound is source of vibration), ocean waves (wind)

5. Why does a fishing bobber not move forward as a wave passes underneath it?

a. Waves transfer energy not matter

6. How does the loudness of a sound wave decrease as you move away from it? (constant, increase, decrease, etc…). What part of the wave is related to loudness?

a. Decreases. Loudness is related to amplitude.

7. Why can we see the lightning before we hear the thunder?

a. Light travels much faster than sound

8. Why does it take 8 minutes for sunlight to reach Earth?

a. Sun is a very large distance away from the earth. Sunlight travels at 300,000 km/s, needs a full 8 minutes to cover that distance.

9. Distinguish between constructive and destructive interference. Draw examples of each.

a. Constructive: Add amplitudes

b. Destructive: Subtract Amplitudes

LIGHT:

1. Describe the electromagnetic spectrum. Compare wavelength, frequency, and energy.

Low W.L/High Frequency/High Energy

High W.L./Low Frequency/Low Energy

Gamma(X-ray(U.V(Visible(Infrared(Microwaves(Radio Waves

2. Why can radio waves travel through space, but sound cannot?

a. Radio waves do not require a medium to travel through

3. What is a ray diagram (think of the mirror maze lab)?

4. Explain refraction.

a. The change in direction of a wave (light, sound etc.) caused by the change in speed brought about by changing the medium it is travelling through.

5. Why does the sun look yellow? Why is the sky blue? Why do sunsets and sunrises appear red and orange?

a. Sun is yellow because as sunlight travels through the atmosphere, the blues/violets are separated out causing us to see yellow. For sunrise and sunset, the light travels through more atmosphere, causing the yellows to also get separated out leaving only the longest wavelengths of light. The sky is blue because the nitrogen and oxygen particles in the atmosphere are roughly the same size as the blue wavelengths of light so those get separated out and “seen.”

ENERGY:

1. Explain the law of conservation of energy and give an example.

a. Energy cannot be created or destroyed, only transformed from one form to another. Example: electricity: energy that comes from the plug is used to power machine and some is lost to environment as heat/sound etc.

2. Why does all of the stored (potential) energy of gas not transfer into mechanical (kinetic) energy of the vehicle?

a. Some of the energy gets lost as heat and sound while being converted.

3. Describe the transfer of potential and kinetic energy as a roller coaster goes up and down a hill. How does the sum of the potential and kinetic energy change during this process?

a. At the top of the hill it is all potential energy, at the bottom all kinetic. The sum never changes, always the same amount of TOTAL energy.

4. Why do all mechanical systems require a force of some kind to maintain their motion?

a. Need to overcome friction to keep moving.

ELECTRICITY:

1. How does the force between two electrons change as they move closer together (Coulomb’s Law)?

a. Increases

2. How does the force between an electron and a positive nucleus change if the size of the charge of the nucleus is doubled(Coulomb’s Law)?

a. Force is doubled

3. Why does acquiring excess static charge (electrons) cause you to “shock” someone if you touch them?

a. You have extra charge in you so those electrons are looking for something/someone to transfer to that doesn’t have an excess charge.

4. How is electricity produced in power plants (give three examples)?

a. Coal burning, nuclear power, hydroelectric

5. What is the difference between voltage, resistance and current in an electric system? How do they relate to each other and to the flow of electrons?

a. Voltage is the pressure of a circuit, resistance is how much the voltage is reduced by/slowed down, current is the rate of the flow of electrons in a circuit. As voltage increases, current increases. As resistance increases, current decreases.

6. What is the difference between a series and parallel circuit in terms of what they look like and how they are used?

a. Series circuit has only one path from start to finish so all loads receive the same amount of current. Parallel have multiple paths so every load does not receive full current.

7. What is a short circuit?

a. Improper wiring that causes a resistor to be passed up and can lead to an overload of electric charge.

8. Explain the difference between a conductor of electricity and an insulator. Give examples of each.

a. Conductors allow electricity to flow through them (copper wire) an insulator does not allow the flow of electricity (rubber)

PRACTICE PROBLEMS:

1. Name a device that transforms the first type of energy into the second:

a. Electrical into heat: Hair dryer

b. Electrical into mechanical: Ferris Wheel, roller coaster

c. Potential into electric: Hydroelectric Dams

2. Identify the following as potential or kinetic energy:

a. A flag blowing in the wind: kinetic

b. The rollercoaster cart at the top of the highest hill waiting to start: potential

c. The rollercoaster cart at the bottom of the lowest valley on the coaster.: kinetic

d. The energy in food: potential

e. The energy in a stretched spring of a mouse trap: potential

3. Draw the following circuits:

a. Open

b. Closed

c. Series with 2 bulbs

d. Parallel with 3 bulbs

Calculations Practice:

1. A wave is moving toward the shore with a velocity of 5.0 m/s. If its frequency is 2.5 hertz, what is its wavelength?

2M

2. A tuning fork has a frequency of 280 HZ, and the wavelength of the sound produced is 1.5 meters. Find the speed of sound.

420m/s

3. What is the potential energy of a rock with a mass of 10 kg that is sitting on top of a hill 300m high?

30,000J

4. What is the kinetic energy of a ball with a mass of 0.25 kg traveling at 3 m/s?

1.125 J

5. A book weighing 3 N is lifted 2 m. How much work is done?

6J

6. How much power was used to lift the book in #5 if it was done in 0.5 s?

12W

7. A boy pushes a lever down 2 m with a force of 75 N. The box at the other end weighs 50 N and moves up 2.5 m. What is the efficiency of this lever?

83.3%

8. How much current flows through a radio speaker that has a resistance of 8 Ohms when 12 V is impressed across the speaker?

1.5A

9. What power is needed to operate a clock radio if it draws a current of 0.5 A from a 120-V circuit?

60W