CFA 3 Review

What design change would increase the magnetic field strength of this electromagnet so that it would lift three paper clips?

• A. Remove the nail from within the coil

• B. Move the battery closer to the nail

• C. Increase the number of loops in the coil

• DYou cannot increase the magnetic field

Answer explanation

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Greta passed a comb through her hair several times. She then placed the comb next to a stream of water flowing from a faucet. Greta observed the stream of water bend toward the comb.

How did passing a comb through her hair allow the comb to bend the stream of water?

• A. by making the comb more absorbent

• B. by giving the comb an electrical charge

• C. by increasing the thermal energy of the comb

• D. by breaking some of the chemical bonds in the comb

Answer explanation

An electrical charge is created when electrons are transferred to or removed from an object. Because electrons have a negative charge, when they are added to an object, it becomes negatively charged. When electrons are removed from an object, it becomes positively charged.

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Which is true about the soccer ball used by Juan?

• A. The velocity of the ball changed.

• B. The density of the ball changed

• C. The speed of the ball remained the same.

• D. The kinetic energy of the ball remained the same.

Answer explanation

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Which of the following graphs shows how the mass of an object affects the amount of force needed to move it?

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• 
• 
• 

Answer explanation

An object’s positive and negative movements can be modeled using a motion map or time-position graph.

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If the action force is applied by the cue ball to the black ball, which force is the reaction force?

• A. the force of gravity on the cue ball

• B. the friction applied by the table to the cue ball

• C. the force applied to the cue ball by the black ball

• D. the force applied by the stick to the cue ball

Answer explanation

-For any pair of interacting objects, the force exerted by the first object on the second object is equal in strength to the force that the second object exerts on the first, but in the opposite direction.

-Equal and opposite forces exist whether or not the objects are moving, and even in a collision where only one object moves.

-The force exerted on an object highlighting that the magnitude of force exerted on an object results in an equal magnitude of force in the opposite direction(cause and effect).

The causes of the motion of an object.

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Which statement best compares the two waves?

• A. The pitch of the sound decreased in Figure 2.

• B. The loudness of the sound decreased in Figure 2.

• C. The velocity of the sound increased in Figure 2.

• D. The wavelength of the sound increased in Figure 2.

Answer explanation

Waves transfer energy from the place where they form (source) to another place.

The behavior of the source of the wave determines the properties of the wave.

The amplitude of a wave is an outcome of the amount of energy being transferred from the source.

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Which numbered sound wave illustrates the greatest amount of time between wave crests?

• A. 1

• B. 2

• C. 3

• D. 4

Answer explanation

Wavelength is inversely proportional to frequency of a wave: waves with higher frequencies have shorter wavelengths; waves with lower frequencies have longer wavelengths.

Frequency is a measurement of how often a recurring event such as a wave occurs in a measured amount of time.

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Collars that emit radio waves are sometimes placed on animals to find their location. Which is the best reason for using radio waves as a method of tracking the animals?

• A. Radio waves are visible.

• B. Radio waves have a high frequency.

• C. Radio waves spread in all directions.

• D. Radio waves are created by the animal.

Answer explanation

In analog technology, a wave is recorded or used in its original form.

In digital technology, the analog wave is sampled and the information is converted into binary (numbers—1’s and 0’s) and then transmitted into wave pulses and stored reliably and recreated at a later time.

Digitized signals are a more reliable way to encode and transmit information.

Digitized signals travel quicker and have less interruptions.

A ship is mapping the structure of the ocean floor using sonar technology. Which statement describes the basic method used in this type of mapping?

• A. A radio wave is sent from the ship and reflects off the ocean floor back to a receiver on the ship.

• B. A sound wave is sent from the ship and reflects off the ocean floor back to a receiver on the ship.

• C. A radio wave is sent by the ship and is absorbed by the ocean floor.

• D. A sound wave is sent by the ship and is absorbed by the ocean floor.

Answer explanation

A wave is a means of transporting energy.

The interaction between waves and their transmitting medium can result in a change in energy of the wave.

Mechanical waves require a medium to move through.

Electromagnetic waves do not require a medium to move and can travel through a vacuum.

Electromagnetic waves and mechanical waves may be refracted, reflected, transmitted or absorbed through various mediums.

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The steady state theory suggested that the universe has always existed and maintains the same structure. This theory was later discredited due to which discovery?

• A. The amount of hydrogen in the universe is extremely high to remain steady.

• B. The scale of the universe is much greater than was previously understood.

• C. The shift of light toward longer wavelengths indicates that most galaxies are moving away from Earth.

• D. More powerful telescopes have made observations of planets orbiting stars other than the Sun.

Answer explanation

The universe began with a period of rapid expansion which resulted in the formation of stars and galaxies—The Big Bang Theory.

All of the colors (frequencies) of light emitted by stars are shifted to longer wavelengths, which is known as a red shift, because all of the colors shift towards the red (longer) wavelengths of light; the motion of the stars emitting the waves is “stretching” the wavelengths of the light as the stars move away(e.g. Doppler effect).

The same red shift is observed in all galaxies, indicating that all galaxies are in motion away from each other and that the galaxies that are the most distant, have the greatest degree of a red shift, indicating that they are traveling away from us at the fastest rate. 

All galaxies are moving away from a central point and must have been set onto this outward trajectory by some initial force.

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