Review: Spring Term Final Exam                                                                                      

 

               

1.      Explain the difference of charging by contact or charging by induction.

 

Induction does not involve physical contact.

 

 

2.      Compare and contrast polarization and charging by induction.

 

Induction requires a wire to the ground to remove charges.  When this wire is removed, the object maintains its charge.  Polarization does not remove charge to the ground.  When the object that causes polarization is removed, the object may return to a neutral charge.

 

 

3.      What is quantization of energy?

 

Charge occurs in discrete amounts in nature. 

 

 

4.      Metals, such as copper and silver, can become charged by induction, while plastic materials cannot.  Explain why.

 

Charge can move to the ground in metals, while charges move very little in insulators like plastic. 

 

 

 

5.      Compare and contrast the force of gravity and the electric force.

 

They are both field forces that are examples of the inverse square law.  Gravity is always an attractive force while the electric force can be attractive or repulsive.  The force of gravity is negligible compared to the strength of the electric force. 

 

 

 

6.      If a current of 80 mA exists in a metal wire, how many electrons pass a given cross section of the wire in 10 minutes?

 

 

 

 

 

 

7.      What does it mean if a charge is at equilibrium with the surrounding charges?

 

The net force acting on the charge is zero. 

 

 

 

8.      A small glass ball rubbed with silk gains a charge of +5.0 μC.  The glass ball is placed 15 cm from a small charged rubber ball that carries a charge of -6.0 μC.  What is the magnitude of the electric force between the two balls?  Is this force attractive or repulsive? How many electrons has the glass ball lost in the rubbing process?


 

 

 

 

 

9.      What type of resistor would provide the data for the following graph?

 

 

The resistor is non-ohmic.

 

 

 

 

 

10.  What factors would cause resistance in a wire to decrease?

 

Decreasing length

Larger diameter

Lower temperature

 

 

 

11.  Assuming electrical energy costs $0.10 per kW•h, calculate the cost of running each of the following appliances for 24 hours if 120 V is supplied to each

a.       An 1100 W microwave oven.

 

 

 

b.      A toaster with a current of 5 Amps.

P = IV = 5 x 120 = 600 W

 

 

 

 

12.  Determine how many joules of energy are used by each appliance in the previous question.

a.       An 1100 W microwave oven.

 

 

 

b.      A toaster with a current of 5 Amps.

 

 

 

13.  A length of wire is cut into five equal pieces.  The five pieces are then connected in parallel, with the resulting resistance being 4.0 Ω.  What was the resistance of the original length of the wire before it was cut up?

 

 

 

Each segment has resistance of R = 20 Ω.

 With all five together in series, the original resistance was 100 Ω. 


 

14.  Generate a list of rules that apply to series circuits.

 

Current is constant.

Voltage across all resistors must add to the voltage across the battery.

Req = Sum of all individual resistors.

 

 

15.  Generate a list of rules that apply to parallel circuits.

 

 

Voltage across resistors in parallel are equal. 

Current divided by parallel components must equal original current.

 

 

 

 

 

 

 

16.  How many electrons pass through one of the 10.0 Ω resistor every second?

 

 

                                                                                    Req of the circuit = 6 Ω

 

 

 

                                                                        I10Ω=0.8 A  (See next question to see how to get this result.)

 

 

0.8 A = 0.8 C/s = 4.96 x 1018 electrons/second

 

 

 

 

 

17.  How much current is in the 20 Ω resistors in the following diagram?

 

 

 

 Req of the parallel component = 4 Ω. 

 

                                                                        Voltage across parallel component = 8 Volts.

 

 

 

 

 

 

 

 


 

18.  In the following circuit, the current in the 3.9 Ω resistor is 0.40 A.

 

 

 

 

 

a.       What is the voltage of the battery? 

The Req of the 4.2 Ω and 9.1 Ω = 2.87 Ω.

The Req of the 2.2 Ω and 7.5 Ω = 1.70 Ω.

The Req of the circuit = 8.47 Ω.

 

         V = IR = 0.40 A x 8.47 Ω = 3.39 Volts

 

 

 

b.      What is the current in the 4.2 Ω resistor? 

 

 

 

 

c.       What is the voltage drop across the 2.2 Ω resistor?  

 

 

 

 

d.      What is the voltage drop across the 7.5 Ω resistor?

 

 

 

 

 

19.  You have seven resistors available, and all of the resistors have a value of 100.0 Ω. How would you connect these seven resistors to produce an equivalent resistance of 175 Ω?  Draw a schematic diagram. 

 

One resistor + 2 resistors in parallel + 4 resistors in parallel.

 

 

20.  Janet wants to find the spring constant of a given spring, so she hangs the spring vertically and attaches a 0.40 kg mass to the spring’s other end.  If the spring stretches 3.0 cm from its equilibrium position, what is the spring constant?

 

 

 

 

 

21.  What happens to the period of simple pendulum when the pendulum’s length is doubled?  What happens when the suspended mass is doubled?

 

The period increases by the square root of 2 when the length is doubled. 

The period remains the same when the mass is doubled.

 

 

 

 

22.  Find the period and frequency of a 12.0 m long pendulum. 

 

 

 

 

 

23.  A pendulum that moves through its equilibrium position once every 1.000 s is sometimes called a “seconds pendulum”. In Tokyo, Japan, a seconds pendulum is 0.9927 m long.  What is the free-fall acceleration in Tokyo?

 

 

 

 

 

24.  A visitor to a lighthouse wishes to determine the height of the tower.  The visitor ties a spool of thread to a small rock to make a simple pendulum, then hangs the pendulum down a spiral staircase in the center of the tower.  The period of oscillation is 12.0 s.  What is the height of the tower?

 

 

 

 

 

25.  How far does a wave travel in one period?

 

One wavelength.

 

 

26.  What happens to the wavelength of a wave on a string when the frequency is doubled?  What happens to the speed of the wave?

 

The wavelength decreases by 1/2.  The speed of the wave remains the same.

 

 

 

27.  If the wavelength of a sound source is reduced by a factor of 2, what happens to the wave’s frequency?   What happens to its speed?

 

The frequency doubles.  The speed remains the same. 

 

 

 

28.  A fire engine is moving at 40 m/s and sounds its horn.  A car in front of the fire engine is moving at 30 m/s and a van in front of the car is stationary.  Which observer hears the fire engine’s horn at a higher pitch, the driver of the fire truck, car, or the van?

 

The driver of the van. 

 

 

 

29.  If a sound seems to be getting louder, which of the following is probably increasing?

a.       Intensity

b.      frequency

c.       speed of sound

d.      wavelength

 

30.  The decibel level of an orchestra is 90 dB, and a single violin achieves a level of 70 dB.  How do the intensity and volume of the sound of the full orchestra compare with those of the violin’s sound?

The intensity of the orchestra is 100 times greater.

The volume of the orchestra is 4 times as great.

 

 

31.  The decibel level of an orchestra is 90 dB, and a single violin achieves a level of 70 dB.  How many violins are needed to equal the intensity and perceived sound level of the orchestra?

 

100 violins

 

 

 

 

32.  Although soldiers are usually required to march together in step, they must break their march when crossing a bridge.  Explain the possible danger of crossing a rickety bridge without taking this precaution.

 

Vibrations could set the bridge in motion if they match one of the bridge’s natural frequencies. 

 

 

 

33.  A man shouting loudly produces a 70 dB sound at a distance of 5.0 m.  How many watts of sound power does the man emit?

 

 

 

 

34.  A rock group is playing in a club.  Sound emerging outdoors from an open door spreads uniformly in all directions.  If the decibel level is 70 dB at a distance of 1.0 m from the door, at what distance is the music just barely audible to a person with a normal threshold of hearing?  Disregard absorption.

 

 

 

 

 

 

 

35.  Describe how P and S waves from an earthquake can be used to determine the epicenter of the earthquake. 

 

P waves are longitudinal (compression) waves that move faster than transverse S waves.  By noting the difference in arrival times of P and S waves at multiple seismograph locations, the epicenter of an earthquake can be triangulated. 

 

 


 

36.  Describe how the Doppler Effect can help to locate a potential tornado.

 

The Doppler signal portrays parts of a storm moving away in red and parts of a storm moving toward in green.  By locating parts of a storm that are moving toward and away from a Doppler source, regions of rotation can be identified. 

 

37.  Describe what a wave barrier is using a boat or a plane as examples.

 

As the source of a wave moves faster, it is able to travel as fast as the wave itself.  All of the waves bunch up.  When riding in a boat, one will experience the front of the boat rising into the air as the boat is moving over the wave barrier.  Once over the wave barrier, the boat again returns to a horizontal position.  When an aircraft overtakes its own sound waves, it creates a sonic boom, or shockwave. 

 

38.  A jackhammer produces a sound level of 90 db at a distance of 1.0 m.  A jet engine produces a sound level of 130 dB at a distance of 20 m.  The sound intensity of the jet engine is how many times as big as that of the jackhammer?  The volume of the jet engine is how many times as big as that of the jackhammer? 

 

Sound intensity of the jet engine is 10,000 times as great as the jackhammer.

Volume of the jet engine is 16 times as great as the jackhammer.

 

39.  Consider two identical wave pulses on a rope having a fixed end. Suppose the first pulse reaches the end of the rope, is reflected back, and then meets the second pulse. When the two pulses overlap exactly, what will be the amplitude of the resultant pulse?

 

Amplitude will be zero.  This is complete destructive interference.

 

 

 

40.  Draw the resultant wave from the addition of the following waves.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


41. Use a ray diagram to show how to find the image of the candle in the mirror.  Is the image real or virtual? 

 

 

 

 

 

 

The image is virtual.

 

 

 

 

 

 

42. Explain how a rainbow forms.

 

Light is made of different wavelengths of light.  As light enters a water droplet, the speed of each wavelength of light slows down, but not equally.  Each frequency (wavelength) interacts with a water droplet a little differently.  The higher frequencies (blue and violet) are slowed more than the lower frequencies (red).  This causes each wavelength to be refracted at slightly different angles.    When light exits the water droplet, the wavelengths have been separated. 

 

 

43.  Explain how polarizing filters work and relate that to how polarized sunglasses help reduce glare when driving.

 

Originally, light passes through both filters.  As one filter is rotated, all light is blocked out.  The polarizing filters block light traveling in either the vertical or horizontal direction.  When the filters are positioned to block out horizontal and vertical light waves, light does not pass through. 

 

 

 

44.              Describe how the lens in the eye focuses light on the retina.

 

The lens is a converging lens which creates an image on the retina.  As the eye looks at objects at varying distances, muscles work to reshape the lens which changes the focal length. 

 

 

 

45.              How does Lasik eye surgery help to correct vision?

 

A laser is used to reshape the lens of the eye which changes its focal length. 

 

 

46.              What color of light mixed with blue light will produce white light? 

 

Yellow

 

 

47.              White light take away red light equals what color of light?

 

Cyan


 

48.              When red light, blue light, and green light are mixed together, white light is produced.  If you mix red paint, blue paint, and green paint, you do not get white paint.  How do you explain this difference?

 

Mixing light adds more frequencies (wavelengths) of light that are visible.  Adding paint will add more pigment that absorbs different wavelengths, effectively removing those wavelengths from what will be reflected.

 

 

 

High

Energy

Low

Energy

Short

Wavelength

Long wavelength

High Frequency

Low Frequency

A

X

 

 

X

X

 

B

X

 

X

 

X

 

C

 

X

 

X

 

X

D

 

X

X

 

 

X

 

 

49. Which two of the above (A-D) do not show characteristics of electromagnetic waves?

 

A & D

 

 

50. Which of the above (A-D) has the characteristic of a X-Ray?

 

B

 

 

51. Which of the above (A-D) has the characteristic of a radio wave?

 

C

 

 

52. What is the wavelength for the FM radio station 104.5 MHz ?

 

 

 

 

53. Jupiter is five times the distance from the sun compared to the Earth.  How does the sunlight intensity incident to Earth compare to the sunlight intensity incident to Jupiter? 

 

The intensity of sunlight incident to Earth is 25 times the intensity that is incident to Jupiter.