PH 115 Final Exam

A charge is accelerated from rest through a potential difference V and then enters a uniform magnetic field oriented perpendicular to its path. The field deflects the particle into a circular arc of radius R. If the accelerating potential is tripled to 3V, what will be the radius of the circular arc?

(√3)R

An RL circuit is connected to a constant DC voltage input of +5 V. When we turn on the power, then at that instant the potential across the inductor will be

-5V

An electron moving in the direction of the +x-axis enters a magnetic field. If the electron experiences a magnetic deflection in the -y direction, the direction of the magnetic field in this region points in the direction of the

-z-axis

Three particles travel through a region of space where the magnetic field is out of the page, as shown in the figure. The electric charge of each of the three particles is, respectively

1 is negative, 2 is neutral, and 3 is positive.

The typical radius of an atom is closer to

10^(-15) m

When accelerated electrons collide with air molecules one of the likely "byproducts" is

A photon

The transformer is a device that can increase the output of the input electric energy. This statement is

Absurd

The ideal gas law describes

All of the above (the momentum exchange from collisions between molecules as a function of temperature, the force exerted by collisions between molecules and the walls where the gas is contained, how fast gas molecules move and collide under different temperatures)

Two resistors in parallel are made of the same material and have the same length and cross section. These two resistors will always have there same

All of these on the list (current, resistivity, voltage, and resistance)

The size of the VDG dome determines

All of these on the list (how long sparks can reach, the electric potential magnitude on the surface of the sphere, and how much charge is stored)

The PV=constant implies that

All on the list (d(PV)=0, dE=0, dT=0)

At it's natural state air is

An electrical insulator

In your lab experiment, you deduced that as the AC source frequency increases in an RC in series, the rms voltage across the resistor

Approaches the rms of the source

The charges on a randomly-shaped conductor always reside

At the surface

The creation of an electromagnet requires

Both AC and DC would work

In your lab experiment, you deduced that the speed of a capacitor discharging in a DC circuit depends on

Both on capacitance and resistance

The plates of an isolated parallel plate capacitor with a capacitance C carry a charge Q. What is the capacitance of the capacitor if the charge is increased to 2Q?

C

Two capacitors in series that have the same charge density and same plate separation will always have the same

Charge

Two wires run by current indeed exhibit attractive forces. This statement is

Correct

Three 10-Ohm resistors in series made from the same material will ALWAYS share the same

Current, voltage, and resistivity

In an AC (sine-wave) domain, the time-series of the voltages between the capacitor and the resistor will ALWAYS be

Exactly 90°

The resistance of the semi-conductor we studied in the lab

Exhibited a non-ohmic behavior

A student argues that the light that is produced during the VDG spark is due to the thermal expansion of the surrounding air. This statement is

False

A transformer is a way to increase the electrical energy from one coil to the adjacent coil. This statement is

False

Both Kirchhoff rules are NOT valid for AC current. This statement is

False

Faraday's law only applies to materials that are paramagnetic (I.e. can be magnetized) such as iron. This statement is

False

In the original newton's law of cooling the type of liquid is utterly irrelevant. This argument is

False

Ohm's law is always obeyed across all electronic devices

False

One argues that because the proton is much larger in mass than the electron, it creates a much stronger electric field at the same distance than the electron does. This statement is

False

Someone argues that a transformer, in fact, increases the electric potential energy of the outer coil. This person's argument is blatantly

False

The neutron is much less massive than the proton

False

The joule's law of heating suggests a linear relationship between temperature and time. What we actually observed was

Far from a straight line

The charges generated by the VDG are because of

Frictional forces

Inductance, the same way as capacitance and resistance in an AC domain are properties of

Geometry

Capacitance depends on

Geometry and dielectric only

The basic function of an oscilloscope is to return the electric potential difference across any element in a circuit with respect to

Ground

The term P*V in the ideal gas law has units of

Joule

The specific heat of two different liquids at the same temperature and pressure are

Likely different

In your DC experiment, when the capacitor was just beginning to charge the current in the circuit was

Macimum

We observed that the temperature probe near the bottom of the canister containing our liquid exhibited

More time variations

Two different resistors in series connected to AC supply will ALWAYS exhibit

No voltage phase difference

The emf field, unlike the coulomb electric field, is

Non-conservative

A Faraday cage can be constructed from

None of these (a non-conductor, an insulator, a semi-conductor)

In an AC (sine-wave) domain, the time-series of the voltages between the capacitor and the entire circuit will ALWAYS be

None of these (exactly 180, 90, in phase)

On which of the following parameters does the heat contained within an ideal gas depend

None of these apply (volume, temperature, and pressure)

The capacitance will increase if one

None of these on the list (increase the plate separation, decrease the charge, increases the voltage)

The sound from the electrostatic luminous spark we observed in the lab is a result of

None of these on the list (photons produced from excited atoms, electron reduction from excited atoms, or electron production from excited atoms)

The transformer we dealt with in this lab was a

None of these on this list (step-down ideal, step-up ideal)

The charges on the VDG reside

On the surface

Ions having equal charges but masses of M and 2M are accelerated through the same potential difference and then enter a uniform magnetic field perpendicular to their path. If the heavier ions follow a circular arc of radius R, what is the radius of the arc followed by the lighter?

R/√2

Two resistors R1 and R2 are run in parallel AC circuit but R1 get's hotter faster than R2. Then it would be safe to assume that

R2>R1

In the lab we experimented on resistors in series in the AC domain. When we increased the frequency without changing anything else, we observed that the current of the circuit

Remained the same

In your lab experiment, you deduced that as the AC source frequency increases in an RC in parallel then the rms voltage across the entire circuit

Remains the same

Ohm's law if applied to two coils in series treats the equivalent inductance the same way as

Resistors

When lowering the frequency in an AC LR circuit then the inductance (L)

Stays the same

Inductive charging is due to

The Coulomb force

One of the major differences between DC and AC is that when the circuit includes a capacitor and a resistor in series then

The capacitance reactance depends on frequency

Heat is a form of energy that relates to the

The energy flow from hot to cold

In your lab experiment, you observed that the discharging capacitor would exhibit

The opposite polarity than it was charged at

The way we tried to simulate an adiabatic decompression in our experiment was by ensuring that

The process was fast

The inductive charging (I.e. the reason why we used the smaller dome in the lab) acquires the opposite charge than the main Van de Graaf (VDG) dome is because

The repelling forces between electrons

From our experiment heating oil and water, we deduced that the speed at which each liquid heats up also can depend on

The size of the molecules of the liquid

Gauss' law for magnetism essentially describes that

There are no magnetic monopoles

The phase difference between the AC voltages of two resistors in series depends on

There is no phase difference (i.e. zero)

During your Boyle's law experiment, why did you wait for a few seconds each time before you pressed down the syringe

To make sure that the process is isothermal

Only an electromagnet can have a north magnetic pole without having a south magnetic pole. This statement is

Totally inaccurate

A vertical wire carries a current vertically upward in a region where the magnetic field vector points toward the north. What is the direction of the magnetic force on this current due to the field?

Toward the west

An electron moving toward the west, enters a uniform magnetic field. Because of this field the electron curves upward. The direction of the magnetic field is

Towards the north

At any given time there are electrons in the air that we breathe

True

Momentum exchange between electron collisions is one of the parameters that determines the resistivity of a wire. This statement is

True

Momentum exchange between electrons is one of the parameters that determines the resistivity of a wire. This statement is

True

Ohm's law in AC and DC domain treats an equivalent resistor (I.e. combining more than one resistors into one) the exact same way. This statement is

True

Someone argues that denser liquids must also have higher specific heat. Solely based on your experimental results, this argument is likely

True

Someone argues that we can freeze a liquid if we apply extreme pressure on it. This argument is

True

The elapsed time we considered in order to find the liquid with the higher specific heat DID play a role. Based on your observations this argument is

True

The electron is less massive than the proton

True

In your lab experiment, you considered a capacitor and resistor in series in AC (sine-wave) domain. Did the time-series of the voltage across the capacitor ever become zero?

Yes

In this lab, you learned that if a coil is connected to a DC source, the moment we turn on the switch the current going through the coil will be

Zero

Inside a Faraday cage the electric field is

Zero

The electric field at the center of the VDG dome is

Zero

An adiabatic process exchanges

Zero heat with the environment

One of the major differences between DC and AC (sine-wave) that when the circuit includes a capacitor is that

capacitor has resistance, but dependent on frequency

An electrostatic luminous spark is a result of

collisions between ions or electrons and air molecules

The breakdown voltage of a gas depends on its

density, temperature, and partial pressure

The area contained under a P-V graph relates to

energy

A charged particle is moving with speed v perpendicular to a uniform magnetic field. A second identical charged particle is moving with speed 2v perpendicular to the same magnetic field. If the frequency of revolution of the first particle is f, the frequency of revolution of the second particle is

f

The relative mean square (rms) quantity for electric potential in AC is always

greater than the numerical average of AC electric potential

A photon has

no charge

Two beakers contain two liquids of the same mass. We heat them to the same final temperature, without any phase changes occurring. The liquid that heats faster has

smaller specific heat than the other

A coil (inductor) is in series with a resistor and AC source. We turn on the power. The moment the current is trying to enter the coil then

the inductor will produce a magnetic field which will further induce a current with direction opposite to the current in the circuit