Sound waves travel through a medium by mechanically disturbing the particles of that medium. As particles in the medium are displaced by the sound wave, they in turn act upon neighboring particles. In this fashion, the wave travels through the medium through a parallel series of disturbed particles. Like in other forms of motion, the rate at which the sound wave travels can be measured by dividing the distance over which the wave travels by the time required for it to do so.

Study 1
A group of students hypothesizes that the velocity of sound is dependent upon the density of the medium through which it passes. They propose that with more matter in a given space, each particle needs to travel a shorter distance to disturb the adjacent particles. Using two microphones and a high speed recording device, the students measured the delay from the first microphone to the second. They chose a variety of media, shown in Table 1, and measured the velocity of sound through each using their two-microphone setup. The results are found in Table 1.

Study 2
The students wanted to test their hypothesis by using the same medium at different densities. To do this, they heated pure water to various temperatures and repeated the procedure described in Study 1. Their results can be found in Table 2.

Jackie read about this experiment and decided to recreate Study 1. She found that each of the velocities she measured are higher than those in the original experiment. What is one possible explanation for this difference?

Sound waves travel through a medium by mechanically disturbing the particles of that medium. As particles in the medium are displaced by the sound wave, they in turn act upon neighboring particles. In this fashion, the wave travels through the medium through a parallel series of disturbed particles. Like in other forms of motion, the rate at which the sound wave travels can be measured by dividing the distance over which the wave travels by the time required for it to do so.

Study 1
A group of students hypothesizes that the velocity of sound is dependent upon the density of the medium through which it passes. They propose that with more matter in a given space, each particle needs to travel a shorter distance to disturb the adjacent particles. Using two microphones and a high speed recording device, the students measured the delay from the first microphone to the second. They chose a variety of media, shown in Table 1, and measured the velocity of sound through each using their two-microphone setup. The results are found in Table 1.

Study 2
The students wanted to test their hypothesis by using the same medium at different densities. To do this, they heated pure water to various temperatures and repeated the procedure described in Study 1. Their results can be found in Table 2.

Assume that density of a substance is the only contributing factor to velocity of sound through that substance. If the students' hypothesis in Study 1 is correct, what might they have predicted for the velocity of sound through lead? (Assume all other values in Table 1 remained the same.)

A scientist observed that when low energy types of electromagnetic radiation (light), such as visible light or ultraviolet light, were shone onto a conductive copper wire incorporated into a circuit with a light bulb as shown in Figure 1, the light bulb did not come on. However, when electromagnetic radiation of a higher energy, such as x-rays or gamma rays, was shone onto the wire, the light bulb did come on, indicating a current (electricity) was produced in the wire. The scientist hypothesized that this effect was due to the fact that electromagnetic radiation of a certain energy was able to overcome the attraction between electrons and protons in the individual atoms of copper in the wire, and liberate an electron to produce the electric current. He called this the photoelectric effect, and did the following experiments to further study this effect.

Figure 1

Experiment 1:

The scientist put a sample of copper in an instrument that can measure the energies of free-moving electrons. He shone a light source capable of producing specific energies of electromagnetic radiation on the metal and slowly increased the energy of the light. The instrument was used to measure the kinetic energies (energy due to motion) of any electrons that were liberated from the copper sample. The scientist recorded the energy of light used in frequency, where a low frequency corresponds to a low energy electromagnetic radiation, and a high frequency corresponds to a high frequency of electromagnetic radiation. He saw that no electrons could be detected at low frequencies, and that after a specific frequency he called the threshold frequency, the kinetic energy of liberated electrons increased linearly with increasing frequency of incident light as shown in Figure 2 below. The data was fitted with a line along which the data falls; the equation describing this line is shown in Figure 2.

Figure 2

Experiment 2:

The scientist removed the light bulb from the circuit shown in Figure 1 and replaced it with an instrument that can measure electrical charge. He then directed his x-ray source at the wire and slowly increased the intensity of the X-ray light while the frequency was held constant at . He monitored the current produced in the wire as the intensity of light increased and recorded the results in Figure 3 below. Intensity of light is measured in photons (a discrete particle, the fundamental unit of light) and charge in C_oulombs_, and like in Experiment 1, a linear equation is fitted to the data and shown in Figure 3.

Figure 3

The value corresponding to the binding energy of an electron to its positively charged nucleus is known as the work function, and corresponds to the y-intercept of the trend line produced when frequency of incident light is graphed against kinetic energy of liberated electrons. What is the work function for copper?

A physicist wishes to study the trajectory of a ball launched horizontally. She varies parameters such as the launching velocity, starting height, and mass of the ball. For each trajectory, she records the time of flight (in seconds) and horizontal displacement (in meters). She assumes air resistance is negligible.

Figure 1

Using all of the data she collects, she constructs the following table:

Table 1

Which of the following variables were controlled in Trial 2?

A student is doing an experiment relating force and distance to work and work and time to power. She is given the following table:

She is also told that:

Power = Work/ Time

Work is in Joules and Time is in seconds. Power is measured in Watts.

If the Watts of power equals the amount needed to light the light bulb attached then the bulb will be lit. If more Watts of power are present, an attached light bulb will burn brighter.

If the student were to do an experiemt with a force of 6 Newtons and a distance of 1 meter, how much work would the student be doing?

A particle separator functions by using a magnetic field and an electric field pointing perpendicularly. When a charged particle is launched into the particle separator, a constant electric force is exerted on the particle proportional to the particle's charge. Additionally, the magnetic field exerts a force on the particle that is in the opposite direction of the electric force and that is proportional to the particle's charge and velocity. A particle will make it through the particle separator only if the opposing magnetic forces and electric forces are equal in magnitude as they will not cause a net change in the particle's direction.

Which of the following statements about the electric field and magnetic field strength is consistent with the information provided in the passage?

A student is doing an experiment relating force and distance to work and work and time to power. She is given the following table:

She is also told that:

Power = Work/ Time

Work is in Joules and time is in seconds. Power is measured in Watts.

If the Watts of power equals the amount needed to light the light bulb attached then the bulb will be lit. If more Watts of power are present, an attached light bulb will burn brighter.

What is a Joule equal to according to the table?

Sometimes scientists need to scale down experiments because collecting full-scale data may not be practical or possible. Most of the time, the data collected during a small scale-experiment is an accurate indicator of full-scale results. For example, research of craters on the Earth’s surface has indicated that the Earth has experienced a history of massive meteor collisions. It has been hypothesized that, amongst other things, these impacting meteorites caused the Earth’s oceans to vaporize. The detrimental effects associated with meteor collisions would have made the planet to be uninhabitable to humans. Due to these adverse effects, an experiment that could produce meteor-sized craters would not be possible in a full-scale setting.

Researchers have developed small-scale experiments that are exemplary of Newton’s three laws of motion. Newton’s first law states that an object in motion will stay in motion unless it is acted on by another force. This phenomenon is known as inertia. The second law comes in the form of an equation that calculates how much force is exerted on two colliding objects with respect to mass and acceleration. In other words force is equal to the mass of an object multiplied by its acceleration. The third law states that for every action there is an equal and opposite reaction. In other words, forces always occur in pairs. A counter force that is equal in magnitude and opposite in direction compliments each force in a particular direction. For example, if you push downwards on a table then the table, in theory, pushes upwards with the same force.

In a particular small-scale exercise, students were asked to design an experiment in which two “meteorites” would be dropped into a medium of sand and the subsequent crater diameters would be measured. Afterwards, the sand would be leveled and the experiment would be repeated. The students were asked to identify all of the factors that could affect the formation of the craters. This was done in order to ensure that each experiment was testing one independent and one dependent variable at a time. Otherwise, it would be unclear which variable is causing the observed effect. Possible variables that could alter the outcome of the experiment included but were not limited to the following: height of the fall, speed of the “meteorite,” angle of impact, and the mass of meteorite.

Consider an experiment that seeks to identify the mass of the meteorite analog. All other variables would have to remain constant in order to ensure accurate results. In order to do this, the height of the fall was set to one meter. The object was placed on top of a vertical meter stick. In order to keep the acceleration and height of the drop constant, it was rolled off of the stick instead of being pushed or simply dropped. Last, a protractor was used to keep the meter stick at a ninety-degree angle. In the procedure, a marble and a golf ball were used as “meteorites” of different masses.

The results of the experiment were recorded in the table and figure provided.

| | Crater Diameter (cm) | | | | --------------------------- | -------------------------- | ---- | | Trial Number | | | | | Marble (mass = 4g) | Golf ball (mass = 46g) | | | 1 | 4.5 | 7.75 | | 2 | 4.5 | 6 | | 3 | 4 | 5.5 | | 4 | 3 | 6 | | 5 | 3 | 6.5 | | 6 | 3.5 | 7 | | 7 | 3 | 5 | | 8 | 3 | 5 | | 9 | 3 | 7 | | 10 | 3.5 | 6 | | | Average | Average | | | | 3.5 cm | 6.175 cm | |

Which factor, other than mass and velocity, would cause the greatest change to the results of the experiment?

An engineer wants to design a prank toy that will be thrown onto the ground. It looks like a superball (bouncing ball), but does not bounce. The engineer has Subtance A, Substance B, and Substance C that he drops from various heights. All of the tests are performed by dropping the substances on the same surface and each height is tested multiple times. The error between experiments is minimal and too small to be seen on the graph. The engineer records the maximum rebound height of each substance at the various drop heights. This data is displayed in the graph below.

Which of the following will be the best improvement that can be made in the design of the experiment?

A scientist observed that when low energy types of electromagnetic radiation (light), such as visible light or ultraviolet light, were shone onto a conductive copper wire incorporated into a circuit with a light bulb as shown in Figure 1, the light bulb did not come on. However, when electromagnetic radiation of a higher energy, such as x-rays or gamma rays, was shone onto the wire, the light bulb did come on, indicating a current (electricity) was produced in the wire. The scientist hypothesized that this effect was due to the fact that electromagnetic radiation of a certain energy was able to overcome the attraction between electrons and protons in the individual atoms of copper in the wire, and liberate an electron to produce the electric current. He called this the photoelectric effect, and did the following experiments to further study this effect.

Figure 1

Experiment 1:

The scientist put a sample of copper in an instrument that can measure the energies of free-moving electrons. He shone a light source capable of producing specific energies of electromagnetic radiation on the metal and slowly increased the energy of the light. The instrument was used to measure the kinetic energies (energy due to motion) of any electrons that were liberated from the copper sample. The scientist recorded the energy of light used in frequency, where a low frequency corresponds to a low energy electromagnetic radiation, and a high frequency corresponds to a high frequency of electromagnetic radiation. He saw that no electrons could be detected at low frequencies, and that after a specific frequency he called the threshold frequency, the kinetic energy of liberated electrons increased linearly with increasing frequency of incident light as shown in Figure 2 below. The data was fitted with a line along which the data falls; the equation describing this line is shown in Figure 2.

Figure 2

Experiment 2:

The scientist removed the light bulb from the circuit shown in Figure 1 and replaced it with an instrument that can measure electrical charge. He then directed his x-ray source at the wire and slowly increased the intensity of the X-ray light while the frequency was held constant at . He monitored the current produced in the wire as the intensity of light increased and recorded the results in Figure 3 below. Intensity of light is measured in photons (a discrete particle, the fundamental unit of light) and charge in C_oulombs_, and like in Experiment 1, a linear equation is fitted to the data and shown in Figure 3.

Figure 3

The circuit setup in Experiment 3 can be considered a solar cell as electricity is produced when the wire collects electromagnetic radiation. An important consideration in the development of solar cells is their efficiency, which can be defined as the ratio of electrons produced to photons incident on the material expressed as a percentage. What is the efficiency of the solar cell in Experiment 2?