Question 1

Andy has a metal sphere that has a charge of 0.5 coulombs on it. He wants to remove some of this charge and place it on a second sphere, and use the two spheres to repel each other. How much charge should be transplanted to produce the greatest force?

Accepted Answer

According to Coulomb's law, the attractive or repulsive force is F = (q1*q2)/r2. From this equation we can see that if we need to split a charge, if q1 =q2 we can produce the greatest force.

Question 2

The discharge of a capacitor is best described by which of the following statements?

Accepted Answer

The discharge of a capacitor follows an exponential curve, and the initial discharge rate is exponentially greater than the discharge rate near T = ?.

Question 3

What is the voltage across a 10 Ohm resistor, if we flow 0.25 amps of current through it?

Accepted Answer

According to Ohm's Law, V = I*R. Thus, V = 0.25*10 in this case, or 2.5 volts.

Question 4

Chad has a super powerful battery capable of producing 30,000 volts! However, to use it safely, he needs to make sure the current flowing through isn't more than 1.5 amps at all times. Which of the following resistors should he use?

Accepted Answer

He should use a resistor with a rating of 20,000 Ohms. This will give the correct rating of 1.5 amps, which actually still isn't safe! A current of about 50 mA is enough to kill someone, regardless of the voltage.

Question 5

Which of the following can be calculated using Gauss' Law?

Accepted Answer

Gauss' Law is used to calculate flux through a surface. It can be applied to objects containing charge or current however, but is not used to calculate the amount of charge or current on the object.

Question 6

If a magnetic field of 10 x 10-5 T is applied perpendicularly to a 1 meter wire carrying 5 amps of current, what will be the force experienced by the wire?

Accepted Answer

The force experienced will be 0.00005 N. The force generated by a magnetic field on a current carrying wire is F = I*L*B*sin(?). Because the field is perpendicular, sin(?) is 1. Thus, F = 5*1*10x10-5, or approximately 0.00005 Newtons.

Question 7

Which of the following is not true about magnetic fields?

Accepted Answer

All of the above are true. Keep in mind that the angle is only important for a current through a wire. For a point charge, the angle at which the magnetic field is applied does not matter.

Question 8

Magnetic field lines flow from:

Accepted Answer

Magnetic field lines flow from North to South. However, this is slightly misleading. 'North' actually means the positive end of the magnet, and 'south' means the negative end of the magnet.

Question 9

Transformers on power lines are an example of which electrical phenomenon?

Accepted Answer

Transformers are very large inductors. Induction is the generation of an electric field with the flow of a charge in a magnetic field.

Question 10

Richard conducts an experiment, and finds the following plot of an object's velocity over time. Which of the following is true about this object?

Accepted Answer

In the graph, we can see the velocity is increasing over time, meaning it is accelerating.

Question 11

In astronomy physics, what is the blue-red shift?

Accepted Answer

The blue-red shift is an example of the Doppler effect on light traveling from distant stars. Red shift occurs when objects are moving away from the observer, and blue shift occurs when objects are moving toward the observer.

Question 12

White dwarf stars or black holes would be examples of:

Accepted Answer

Weakly interacting massive particles are superdense dark matter systems, including white dwarf stars or black holes. These particles are not 'weak', but rather interact with weak force and gravitational force.

Question 13

According to modern physics, one theory for the beginning of the universe is the:

Accepted Answer

The big bang theory is one of the primary theories for the beginning of the universe. In the big bang theory, it is proposed that at one point the universe was condensed into an ultra-dense ball of matter, which then exploded. This theory accounts for the continuing rapid expansion of the universe.

Question 14

Some of the theories developed by Einstein gave in part the equation E = mC?, which associates energy with:

Accepted Answer

E = mC² relates energy with mass and the speed of light. This is the mass energy equivalence that states that the mass of an object is related to the energy that it contains.

Question 15

Which of the following statements concerning radiation is not true?

Accepted Answer

Radiation entering the earth's atmosphere includes light, ultraviolet, infrared, and electromagnetic radiation, but not gamma radiation. If gamma radiation struck earth on a large scale, most life would be wiped out.

Question 16

After striking a tuning fork, Sam finds that if he places the humming fork next to his piano, some of the piano strings vibrate as well. This phenomenon is called:

Accepted Answer

Many objects have a resonant frequency, at which frequency the will resonate (or vibrate) with an object that is already vibrating at that frequency. This phenomenon is known as resonance.

Question 17

An airplane is flying at 400 mph, and encounters a wind blowing across the plane (from right to left), at a speed of 35 mph. The plane's speed relative to the ground will:

Accepted Answer

Although the wind is blowing a right angle to the plane's direction, it will still increase the groundspeed of the plane. The new vector of the plane will be ?4002 + 352, and its groundspeed will be 401.5 mph.

Question 18

Christine accidentally drives her car into a tree, and the car experiences 4250 N of force, crushing the front hood. How much force does the poor tree experience?

Accepted Answer

According to Newton's law's, for each action, there is an equal and opposite reaction. Thus, if the car experienced 4250 N of force, the reacting object (the tree) must also experience that amount of force.

Question 19

Consider a mixture of nitrogen, oxygen, carbon dioxide, and hydrogen, molecules that are commonly found in Earth's atmosphere. At the same temperature and pressure, which of these molecules is moving the fastest?

Accepted Answer

At a given temperature, each gas molecule contains roughly the same amount of energy. However, because the hydrogen molecule weighs the least, it will be moving the fastest, according to the equation for kinetic energy, E = 1/2mv2. If E is held constant, then if mass is reduced, velocity must increase.

Question 20

Which of the following is true about the speed of sound?

Accepted Answer

The speed of sound depends on the material it is traveling through, and is not always a fixed constant. The speed of sound in air is about 760 mph, but the speed of sound in water is about 4.5 times that, at nearly 3300 mph.

Quiz 28: Physics