Download Test 3/Chapter 9-11 Sample Questions - Answers

PHS 112
Test 3 Review
Chapters 9-11
How are the interactions between charges like the interactions between magnetic poles?
Like charges/poles repel and opposite charges/poles attract. The strength of these interactions correspond to the inverse
square rule.
A magnet attracts a metal tack. How does the force of a magnet attracting a tack compare to the force of the tack attracting the magnet? They are equal.
What motion of electrons contributes most to the magnetism of iron atoms (and most similar magnetic substances)?
The spin of electrons around their axis.
Even in a piece of iron that is not a magnet, the individual atoms are magnets. How is this possible?
Each iron atom has many spinning electrons each creating a magnetic field. The magnetic fields of electrons spinning in
opposite directions cancel each other. But each iron atom has more electrons spinning one way than the other so there is
a net magnetic field.
False (T/F) An iron nail may be more attracted by the north pole of the magnet than the south pole.
True. The domains rearrange randomly. (T/F) A magnet is weakened when heated to a high temperature.
False (T/F) When a magnet is broken in half, each piece of the magnet is half as strong.
False. They circle the wire. (T/F) Magnetic field lines of a current-carrying wire extend straight out from the wire.
A current-carrying coil has a magnetic field inside it. How can the strength of the magnetic field be increased?
Increase the current flowing in the coil. Add more loops to the coil. Put a piece of iron in the coil (electromagnetic).
True (T/F) The earth is one big magnet.
True (T/F) Magnetic force acts most strongly on a current-carrying wire if they are perpendicular.
(This is how the earth’s magnetic field protects us from the charged particles in the solar wind.)
True (T/F) An electric motor and a generator are very similar devices.
(In one current is put in to do work, while in the other work is done to put out current.)
Whose law describes . . .
electromagnetic induction?
Faraday’s Law
the connection between current, voltage, and resistance?
Ohm’s Law
A changing magnetic field induces a voltage in a coil (ex. moving a magnet in a coil). How can the voltage be increased?
Stronger magnet. Faster change in the magnetic field (move magnet faster). More loops in the coil.
True Metal detectors work by magnetic induction. (T/F) This makes them more sensitive to the presence of some metals than others.
True (T/F) Generating electricity does not produce energy.
A transformer has a primary coil with twice as many loops as the secondary coil. Will the voltage be increased or decreased? By how much?
Output voltage will be decreased to ½ the input voltage.
12 volt dc current is run through the primary coil of a transformer. What is the voltage in the secondary coil with twice as many loops?
Zero. As a direct current flows it creates a magnetic field. Since direct current continues to flow in one direction the
magnetic field is constant. Induction of a voltage in the secondary coil requires a change in the magnetic field.
True (T/F) Electric and magnetic fields combine to produce electromagnetic waves.
False (T/F) A pendulum swings faster when the string is longer.
True (T/F) This is an example of transverse waves. How many waves are shown? 6
False. Crest to midpoint. (T/F) Amplitude is the vertical distance from crest to trough.
What is the relationship between frequency and period?
As frequency increases, the period decreases proportionately. Inveresely proportional.
A longitudinal wave has alternating regions of compression and rarefaction.
False (T/F) The substance through which the wave travels moves along with the wave.
A frequency of 250 Hz corresponds to 250 waves or cycles per second.
As the frequency of waves increase the wavelength of waves decreases. Frequency and wavelength are inversely proportional.
True (T/F) We can hear 250 Hz sound waves but not 250 Hz radio waves.
Which are longitudinal? Sound waves
Which are electromagnetic? Radio waves
Distinguish between longitudinal waves and transverse waves.
For longitudinal waves the vibration creating the wave occurs in the same direction that the wave travels. So the motion
of the wave is parallel to the path of the wave.
For transverse waves the direction of the vibration is at right angles to the direction the wave travels. The motion of the
wave is perpendicular to the path of the wave.
About how long does it take for sound to travel one mile? About 5 seconds
False. Reflection (T/F) Echos are due to refraction of sound.
True (T/F) Refraction always requires a difference in speed.
False. Faster in warm air. (T/F) Sound travels faster in cool air than in warm air. What other factors effect the speed of sound? Wind, humidity
What are the two types of interference? Constructive and destructive.
What beat frequency is heard for a 250 Hz tone with a 253 Hz tone? Three beats per second.
True. Higher pitch. (T/F) As we rapidly approach a sound, its frequency increases. True. Shifts toward blue. (T/F) This is also true for light.
False. (T/F) Once a plane passes the sound “barrier” and is moving faster than sound, it no longer causes a sonic boom.
Waves “pushed together into sonic boom whenever it is exceeding the speed of sound.
The volume of a sound depends on this property of the wave. Amplitude
Distinguish between fundamental frequency and harmonics.
The fundamental frequency is the lowest tone in a musical note. Musical instruments create harmonics, or whole number
multiples of the fundamental frequency, at the same time.
False. Sound waves cannot move through a vacuum but electromagnetic waves can. (T/F) Waves cannot move through a vacuum.
Electromagnetic waves are induced by vibrating electrons.
Light and sound move from air to water. Which speeds up and which slows down? Sound speeds up and light slows down.
False (T/F) Radio waves have a higher frequency than light.
The energy of light absorbed by an opaque substance is usually turned into thermal energy.
Describe how light is transmitted through glass. It is absorbed and reemitted by electrons many times along its path through glass .
What is diffuse reflection?
Reflection in many directions by a surface that is rough compared to the wavelength of the incoming waves.
True (T/F) The colors from a TV are the result of addition. What about the “colors” on this page?
Colors on a page are due to subtraction of colors.
What are the colors of light in a continuous spectrum (like a rainbow) in order? ROYGBIV Red, orange, yellow, green, blue indigo, and violet
Why is the sky blue? Oxygen and nitrogen in the atmosphere scatter blue light more than the other colors.
For the maximum amount of light to pass through a pair of polarizing filters there axes must be aligned in the same direction.
Primary additive colors combine to form this color. white
Complementary additive colors combine to form this color. White
For subtractive colors these answers would be black.