Unit 4 homework conceptual questions

Question 1

What physical process was involved with the collapse of the Tacoma Narrows bridge?

Answer 1

Resonance

Question 2

What is a harmonic oscillator?

Answer 2

A harmonic oscillator is a system whose motion is repeated at regular time intervals.

Question 3

_____ ______ is the tendency of a mechanical system to respond at greater amplitude when the frequency of its oscillations matches the system’s natural frequency of vibration

Answer 3

mechanical resonance

Question 4

What is meant by a “restoring” force?

Answer 4

A restoring force is a force that always acts in a direction to bring a system back to its equilibrium position.

Question 5

What are the definitions of the period and frequency of a harmonic oscillator, and how are they related?

Answer 5

The period of an oscillator is the time it takes to complete one full cycle. The frequency of an oscillator is the number of full cycles it completes every second.T and f are reciprocals,
T = 1/f,f = 1/T.
where t = period and f= frequency

Question 6

Why does the pendulum not stop when it reaches its lowest point?

Answer 6

At the bottom of its swing, the pendulum is moving, so its inertia prevents it from stopping.

Question 7

If a pendulem is in between its poles it has ____ ____

if it is at either peak of its pole it has _____ ____

Answer 7

kinetic energy

potential energy

Question 8

If the frequency of a harmonic oscillator is 10 Hz, what is its period?

Answer 8

1/10 seconds

Question 9

A pendelum that is halfway between its mid swing and its pole has energy = to

Answer 9

KE +PE

Question 10

What is a mechanical wave?

Answer 10

A mechanical wave is a disturbance that propagates through a medium.

Question 11

Why are waves important?

Answer 11

Waves are important because they provide a mechanism for the transport of energy without the transport of matter.

Question 12

A _____ ____ is a disturbance that propagates through a medium.

Answer 12

Mechanical wave

Question 13

What is the difference between a transverse and a longitudinal wave?

Answer 13

In a transverse wave segments of the medium vibrate in a direction that is perpendicular to
the direction of the wave. Example: a wave on a string. In a longitudinal wave segments of
the medium vibrate back and forth along the same direction that the wave propagates.
Example: a sound wave.

Question 14

Example of a ______ wave: a wave on a string.

Answer 14

transverse

Question 15

Example of a _______ wave: a sound wave

Answer 15

longitudinal

Question 16

What properties of the air changes when a sound wave propagates through it?

Answer 16

A sound wave causes changes in the pressure and density of the air.

Question 17

speed of sound in miles per second

Answer 17

The speed of sound is approx 1/5 miles per second

Question 18

What are:

a) the wavelength of a wave
b) frequency of a wave
c) how are they related?

Answer 18

a) The wavelength ( lambda) of a wave is the spatial distance over which the wave is repeated. It is the distance between successive wavelengths.
b) The frequency ( f ) of a wave is the number of wave cycles occurring each second.

c)Wavelength and frequency are related by
the periodic wave relation: (lambda)(f) = v (where v is in m/s)

Question 19

What characteristic of a tuning fork determines the frequency of the sound wave that it produces?

Answer 19

The frequency of the sound wave produced by a tuning fork depends on its length. Long tuning forks produce low frequency sound waves and short tuning forks produce high frequency sound waves.

Question 20

Why does a pipe organ need a variety of both long and short pipes?

Answer 20

The tone produced by air blowing through a pipe depends on the length of the pipe. Many pipes of different lengths are needed to cover a large range of tones.

Question 21

What effect gives rise to standing waves?

Answer 21

Standing waves are the result of wave interference.

Question 22

When two violinists play slightly different notes at the same time, the combined sound has a pulsing character. What is the cause of this pulsation?

Answer 22

When sound waves of 2 slightly different frequencies are formed, one hears “beats” or pulsations in the combined waves. The beats are caused by wave interference.

Question 23

1)What particles are in the atom, and what electric charges do they have?

2)Which particles are
in the nucleus of the atom?

3)Does matter typically have a net charge?

Answer 23

1) Atoms contain electrons that are negatively charged, protons that are positively charged, and neutrons that are uncharged.
2) The nucleus contains the protons and neutrons.

3)Although
matter contains enormous numbers of positive and negative charges, it is typically neutral
since in their normal state atoms contain equal numbers of protons and electrons.

Question 24

What is the difference between gravitational and electrical forces?

Answer 24

Gravitational forces are always attractive, whereas electric forces can be attractive or repulsive.

Question 25

_______ forces are always attractive, whereas _____ forces can be attractive or repulsive.

Answer 25

Gravitational

Electric

Question 26

Who discovered the law of force between electric charges?

Answer 26

Coulomb

Question 27

What is the difference between conductors and non‐conductors?

Answer 27

Conductors have free electrons that can roam around whereas non‐conductors do not have
free electrons. Every electrons in a non‐conductor is firmly bound to a particular atom.

Question 28

What charge transfer occurs when
(a) plastic is rubbed with fur, and

(b) glass is rubbed with silk?

Answer 28

(a) When plastic is rubbed with fur electrons are transferred from the fur to the plastic giving it a negative charge.
(b) When glass is rubbed with silk, electrons are transferred from the glass to the silk, leaving the glass with a net positive charge.

Question 29

Why is an uncharged conducting sphere attracted to a charged rod?

Answer 29

An uncharged metal sphere has free electrons that can move around inside it. When a negative rod is brought near an uncharged metal sphere, the electrons in the sphere are pushed away from the side of the sphere closest the rod and move to the other side of the sphere. As a result, the side of the sphere closest to the rod contains an excess of positive charges which are attracted to the negative charges on the rod. Because the excess
electrons that moved away from the rod are farther away from the rod, the repulsive force on them is smaller than the attractive force between the positive charges and the rod. If a
positively charged rod is brought near the uncharged metal sphere, electrons in the sphere move closer to the rod and there is still an attractive force.

Question 30

How can a stream of water or a wooden board moved by a charged rod?

Answer 30

Water molecules H2O have a positive side and a negative side – we call this a dipole. In general, the water molecules are all randomly oriented. However, when a negatively charged rod is brought near a stream of water, the water molecules rotate until the positive
side is closest to the negative rod. This produces an attractive force. In materials like wood, that are called “dielectrics” the molecules get stretched a little bit, so that the positive and negative charges do not exactly cancel.

Question 31

What instrument is used to detect the presence of electric charge?

Answer 31

An electroscope

Question 32

What is the cause of the sparking that occurs when a grounded rod is brought near a van de Graff?

Answer 32

The sparks are an indication that electrons from the van de Graff are jumping to the
grounded rod, and these electrons have enough energy to ionize and excite some of the air molecules. When molecules and atoms get excited they emit light.

Question 33

What is electric current?

Answer 33

An electric current is a flow of electric charges

Question 34

What is the meaning of the statement that there is a fundamental quantity of electric charge?

Answer 34

There is an elementary quantity of electric charge: +-1.602E-19 C

No charge smaller than this exists in nature. Any amount of charge must contain an integral number of
elementary charges. We call this phenomenon charge quantization.

Question 35

Being inside a car may provide some protection from lightening. What is the physical principle underlying this effect?

Answer 35

Electric fields do not penetrate into a conducting enclosure. Any charge placed on a conducting enclosure is on the outside surface. This is called electrostatic shielding. Since a car is mostly metal, it offers some protection in a lightning storm.

Question 36

Under what conditions is water a conductor of electricity?

Answer 36

Pure water is not a conductor of electricity, but water containing ions is a conductor. The water
must contain positive and negative ions to conduct electricity.

Question 37

Under what conditions is a gas a conductor of electricity?

Answer 37

A neutral gas is not a conductor of electricity. However, if a large voltage is applied across a
container of gas, some of the gas molecules will be ionized, i.e., will lose an electron, and thus the gas will become a conductor. A gaseous conductor is called a plasma.

Question 38

What are the basic constituents of a battery?

Answer 38

A battery contains two different metals and some substance, usually an acid, which allows current to flow through it.

Question 39

How is electric current defined and in what units is it measured?

Answer 39

Current is the rate of flow of charge: I=1/t, where q is the charge. Current is measured in Coulombs per second, and 1 C.s is defined as 1 Ampere (A).

Question 40

What effect does a battery produce in an electric circuit?

Answer 40

A battery is a pump for electric charges in a circuit. The potential difference established across a conductor by a battery produces an electric field within the conductor that pushes the electrons that carry the current.

Question 41

What gives rise to electrical resistance in a conductor?

Answer 41

Electrical resistance in a conductor is caused by the fact that as electrons move through the conductor, they collide with the ions which slows them down and causes them to move in zig‐zag paths.

Question 42

What is the relation between, current, voltage, and resistance in a circuit?

Answer 42

Voltage = I * R

Question 43

What is the meaning of the electrical power consumed in a circuit and how is it calculated?

Answer 43

As electrons move through a conductor and collide with the ions, heat is produced. The amount of heat energy produced each second is the electrical power dissipation. P=IV=I^2R

Question 44

Why are power strips, devices having multiple electrical outlets, limited by a current rating?

Answer 44

When multiple appliances are plugged into an outlet, each draws current. The maximum electrical current that the power strip can handle safely is the current rating.

Question 45

What is the difference between series and parallel connections of elements in a circuit, e.g., light bulbs?

Answer 45

Devices connected in series have the same current passing through them. Devices connected in parallel have the same voltage across them.

Question 46

What is direct current or DC?

Answer 46

With direct current or DC, the current always flows in one direction. Direct current is produced by batteries.

Question 47

What is alternating of AC electrical power?

Answer 47

With alternating current AC power the current reverses direction 60 times per sec.