Physics II

Week 1

Week 1 Assignment

Please solve the following problems. You must show all work for full/partial credit. When complete, attach a typed cover sheet and submit to the assignment drop-box.

Question 1 (16 points):

a)      If the electron were moved twice the distance away from the proton, would the electrical force be:

1)      2

2)      ½

3)      4

4)      ¼

b)      If the initial electric Force is, F, and the electron were moved to one third the original distance toward the proton, what would be the new electrical force?

Question 2 (14 points):

What is the magnitude and direction of the electric field at a point 0.75 m away from a point charge of +2.0 pC?

Question 3 (20 points)

Two fixed charges -4.0 µC and -5.0 µC, are separated a certain distance.

a)      Is the net electric field at a location halfway between the two charges:

1)      Directed toward the -4.0 µC charge

2)      Zero

3)      Directed toward the -5.0 µC charge

Prove your answer here.

b)      If the charges are separated by 20 cm, calculate the magnitude of the net electric field halfway between the two charges.

Question 4 (17 points)

What is the speed of a proton whose kinetic energy is 12.9 keV?

Question 5 (17 points)

An electron is accelerated by a uniform electric field (1000 V/m) pointing vertically upward.

a)      Use energy methods to get the magnitude and direction of its velocity after it moves 0.10 cm from rest.

b)      Does the electron gain or lose potential energy?

Question 6 (16 points)

How much charge flows through a 12-V battery when a 2.0 mF capacitor is connected across its terminals?

Week 2

Question 1 (17 points):

How long would it take for a net charge of 2.5 C to pass a location in a wire if it is to carry a steady current of 5.0 mA?

Question 2 (18 points):

Two copper wires have equal lengths, but the diameter of one is three times that of the other.

a)      The resistance of the thinner wire is ____ times that of the thicker wire: (prove your work)

1)      3

2)      ⅓

3)      9

4)      ¼

b)      If the t wire has a resistance of 1.0 Ω, what is the resistance of the thinner wire?

Question 3 (17 points)

A 200 – W computer power supply is on 10 hours per day. If the cost of electricity is $0.15/kWh, what is the cost (to the nearest dollar) to run the computer every day for a year (365 days)?

Question 4 (5 points)

What is the emf of a battery with an internal resistance of 0.15 Ω if the battery delivers 1.5 A to an externally connected 5.0 Ω resistors?

Question 5 (16 points)

Three resistors of value 1.0 Ω, 2.0 Ω, and 4.0 Ω are connected in a parallel circuit with a 6.0 V battery.

a)      What is the total equivalent resistance?

b)      What is the voltage across each resistor?

c)      The power delivered to the 4.0 Ω resistor?

Question 6 (10 points)

What is the equivalent capacitance of two capacitors of 0.40 µF and 0.60 µF when they are connected in:

a)      Series?

b)      Parallel?

Question 7 (17 points)

Three capacitors of equal capacitance are connected in parallel to a battery, and together they draw a certain amount of charge Q from that battery.

a)      Will the charge on each capacitor be:

1)      Q

2)      3Q

3)      Q/3

b)      Three capacitors of 0.25 µF in each parallel connected to a 12-V battery. What is the charge on each capacitor?

c)      How much charge is drawn from the battery?

Week 3

Question 1 (14 points):

If a charge particle moves in a straight line and there are no other forces on it, except possibly from a magnetic field, can you say with certainty that no magnetic field is present? Explain.

Question 2 (14 points):

In a velocity sector, the uniform magnetic field of 1.5 T is produced by a large magnet. Two parallel plates with a separation of 1.5 cm produce the perpendicular electric field. What voltage should be applied across the plates so that:

a)      A singly ionized ion traveling 8.0x10⁴ m/s will pass through undeflected

b)      A double ionized ion traveling at the same speed will pass through undeflected

Question 3 (14 points)

A horizontal magnetic field of 1.0x10⁻⁴T is at an angle of 30° to the direction of the current in a straight wire 75 cm long. If the wire carries a current of 15 A, what is the magnitude of the force on the wire?

Question 4 (15 points)

An electron travels at a speed of 2.0x10⁻⁴ m/s through a uniform magnetic field of strength 1.2x10⁻³T. What is the magnitude of the magnetic force on the electron if its velocity and the magnetic field:

a)      Are perpendicular

b)      Make an angle of 45°

c)      Are parallel

d)      Are exactly opposite

Question 5 (14 points)

A square loop of wire with sides of length 40 cm is in a uniform magnetic field perpendicular to its area. If the field’s strength is 100 mT and it decays to zero in 0.010 seconds:

a)      What is the magnitude of the average emf induced in the loop?

b)      What happens to the emf if the side lengths are reduce by a factor of ½?

Question 6 (15 points)

The armature of an ac generator has 100 turns. Each turn is a rectangular loop measuring 8.0 cm by 12 cm. The generator has a sinusoidal voltage output with an amplitude of 24 V. If the magnetic field of the generator is 250 mT:

a)      With what frequency does the armature turn?

b)      If you double the B and cut  in half, how does this affect the amplitude?

Question 7 (17 points)

An ac generator supplies 20 A at 440 V to a 10,000 V power line. If the step up transformer has 150 turns in its primary coil, how many turns are in the secondary coil?

Week 4

Question 1 (16 points):

An antenna is connected to a car battery. Will the antenna emit electromagnetic radiation? Why or why not? Explain.

Question 2 (17 points):

A light-year is a measure of distance (not time). How many meters does light travel in a year?

Question 3 (17 points)

How long does it take a laser beam to travel to the Moon and back? Take the Earth Moon distance to 384,000 km.

Question 4 (16 points)

A beam of light is incident on a plane mirror at an angle of 35°. If the mirror rotates through a small angle Ɵ, through what angle will the reflected ray rotate?

Question 5 (17 points)

The speed of light in polythene is 1.99x10⁸ m/s. What is the index of refraction of polythene?

Question 6 (17 points)

A beam of light with red and blue components of wavelengths 670 nm and 425 nm, respectively, strikes a slab of fused quartz at an incident angle of 30°. On refraction, the different components are separated by an angle of 0.001312 rad. If the index of refractions of the red light is 1.4925, what is the index of refraction of the blue light?

Week 5

Question 1 (10 points):

The walls of a blackbody cavity are at a temperature of 27° C. What is the frequency of the radiation of maximum intensity?

Question 2 (10 points):

Assume that a 100 – W light bulb gives off 2.50% of its energy as visible light. How many photons of visible light are given off in 1.00 min? (Use an average visible wavelength of 550 nm)

Question 3 (10 points)

What is the energy of photons (joules) emitted by a 107.5 MHz FM radio station?

Question 4 (10 points)

What is the longest wavelength of light that will emit electrons from a metal whose work function is 3.50 eV?

Question 5 (20 points)

A metal with a work function of 2.40 eV is illuminated by a beam of monochromatic light. If the stopping potential is 2.5V, what is the wavelength of the light?

Question 6 (10 points)

What is the de Broglie wavelength of a 1000 kg car moving at a velocity of 25 m/s?

Question 7 (20 points)

A hydrogen atom in its ground state is excited to the n=5 level. It then makes a transition directly to the n=2 level before returning to its ground state.

a)      What are the wavelengths of the emitted photons?

b)      Would any of the emitted wavelengths be in the visible region?

Week 6

Question 1 (17 points):

What is the minimum uncertainty in the velocity of an electron that is known to be somewhere between 0.050 nm and 0.10 nm from a proton?

Question 2 (16 points):

The energy of the first excited state of a hydrogen atom is -0.34 eV ± 0.0003 eV. What is the average lifetime for this state?

Question 3 (17 points)

Knowing that a free neutron has a mean life of 900 s and a mass of m = 1.67 x 10⁻²⁷kg, what is the uncertainty in its mass in kg?

Question 4 (17 points)

For n=5, l = 4, what are the possible values of ml and ms?

Question 5 (17 points)

Draw the ground state energy level diagrams for nitrogen (N) and potassium (K).

Question 6 (17 points)

Calculate the magnitude of the angular momentum of an electron in the n = 7, l = 5 state of hydrogen.

Week 7

Question 1 (10 points):

What is the approximate radius of ?

Question 2 (10 points):

a)      What is the approximate radius of a nucleus?

b)      Approximately what is the value of A for a nucleus whose radius is 3.0x10-15m?

Question 3 (20 points)

Calculate the binding energy per nucleon for a ? nucleus.

Question 4 (10 points)

In the reaction , what is the energy of the  ray emitted here?

Question 5 (10 points)

Polonium-214 can decay by alpha decay.

a)      The product of its decay has how many fewer protons than Polonium-214?

b)      Write the nuclear equation for this decay.

Question 6 (20 points)

Write the nuclear equation for the decay of ? If there are any alpha, beta, or gamma particulars created, what is their maximum kinetic energy created?

Question 7 (10 points)

Francium-223 () has a half-life of 21.8 min.

a)      How many nuclei are initially present in a 25.0 mg sample?

b)      How many nuclei are present 1h and 49 min later?

Question 8 (10 points)

What is the activity of a sample of  that contains 8.9 x 1022 nuclei?

Week 8

Question 1 (20 points):

Complete the follow nuclear reactions:

a)     

b)     

c)     

d)     

Question 2 (20 points):

Consider the reaction

a)      Use the masses of the nuclides involved to determine where it is endogenic or exoergic.

b)      If it is exoergic, find the amount of energy released. If it is endogenic, find the threshold energy.

Question 3 (20 points)

Find the threshold energy for the following reaction:

Question 4 (20 points)

Find the threshold energy of the following reaction:

Question 5 (20 points)

Calculate the energy released in the fission reaction: