AP Physics 2 Unit 15 practice questions

Question 1

Consider the ground state (n=1) of a hydrogen atom (Z=1) and the ground state (n=1) of a singly ionized helium atom (Z=2). How does the ionization energy of the helium ion compare to the ionization energy of the hydrogen atom?

Accepted Answer

The helium ionization energy is four times that of hydrogen.

Answer

The helium ionization energy is two times that of hydrogen.

Answer

The helium ionization energy is one-half that of hydrogen.

Answer

The helium ionization energy is one-fourth that of hydrogen.

Question 2

According to the Bohr model, an electron's orbit circumference must equal an integer multiple of its de Broglie wavelength. How does the electron's wavelength in the n=3 state compare to its wavelength in the n=1 state?

Accepted Answer

The wavelength in the n=3 state is three times the wavelength in the n=1 state.

Answer

The wavelength in the n=3 state is nine times the wavelength in the n=1 state.

Answer

The wavelength in the n=3 state is one-third the wavelength in the n=1 state.

Answer

The wavelength in the n=3 state is one-ninth the wavelength in the n=1 state.

Question 3

In the Bohr model, the electric force between the nucleus and the electron provides the necessary centripetal force. How does the magnitude of this electric force in the n=2 state compare to the magnitude in the n=1 state?

Accepted Answer

The force in the n=2 state is one-sixteenth the force in the n=1 state.

Answer

The force in the n=2 state is one-fourth the force in the n=1 state.

Answer

The force in the n=2 state is one-eighth the force in the n=1 state.

Answer

The force in the n=2 state is one-half the force in the n=1 state.

Question 4

An electron of mass m and charge -e moves in a stable circular orbit of radius r around a nucleus of charge +Ze. Coulomb's constant is k. Which of the following expressions correctly represents the speed v of the electron derived from the balance of forces?

$v = \sqrt{\frac{kZe^2}{mr}}$

$v = \sqrt{\frac{kZe}{mr}}$

$v = \sqrt{\frac{kZe^2}{mr^2}}$

$v = \sqrt{\frac{kZ^2e}{mr}}$

Accepted Answer

$v = \sqrt{\frac{kZe^2}{mr}}$

Answer

$v = \sqrt{\frac{kZe}{mr}}$

Answer

$v = \sqrt{\frac{kZe^2}{mr^2}}$

Answer

$v = \sqrt{\frac{kZ^2e}{mr}}$

Question 5

An electron of mass m orbits a nucleus of charge +Ze at a distance r. Assuming the electric force provides the centripetal acceleration, which expression represents the kinetic energy K of the electron?

$K = \frac{kZe^2}{2r}$

$K = \frac{kZe^2}{r}$

$K = -\frac{kZe^2}{2r}$

$K = -\frac{kZe^2}{r}$

Accepted Answer

$K = \frac{kZe^2}{2r}$

Answer

$K = \frac{kZe^2}{r}$

Answer

$K = -\frac{kZe^2}{2r}$

Answer

$K = -\frac{kZe^2}{r}$

Question 6

An electron of charge -e and mass m orbits a nucleus of charge +Ze in a circle of radius r. Which expression represents the equivalent electric current I generated by this orbiting electron?

Accepted Answer

$I = \frac{e^2}{2\pi} \sqrt{\frac{kZ}{mr^3}}$

Answer

$I = \frac{e}{2\pi} \sqrt{\frac{kZ}{mr^3}}$

Answer

$I = \frac{e^2}{2\pi} \sqrt{\frac{kZ}{mr}}$

Answer

$I = \frac{e}{2\pi} \sqrt{\frac{kZ}{mr}}$

Question 7

An electron of mass m moves with speed v in a circular orbit around a nucleus. Assuming the potential energy is zero at infinity, which expression represents the total mechanical energy E of the system?

$E = -\frac{1}{2}mv^2$

$E = \frac{1}{2}mv^2$

E = -mv^2

E = mv^2

Accepted Answer

$E = -\frac{1}{2}mv^2$

Answer

$E = \frac{1}{2}mv^2$

Answer

E = -mv^2

Answer

E = mv^2

Question 8

A physicist compares a photon of ultraviolet light with frequency $$f_{UV}$$ to a photon of infrared light with frequency $$f_{IR}$$, where $$f_{UV} = 100 f_{IR}$$. Which statement correctly compares the energy $$E_{UV}$$ of the ultraviolet photon to the energy $$E_{IR}$$ of the infrared photon?

Accepted Answer

$$E_{UV}$$ is $$100$$ times $$E_{IR}$$ because energy is directly proportional to frequency.

Answer

$$E_{UV}$$ is $$0.01$$ times $$E_{IR}$$ because energy is inversely proportional to frequency.

Answer

$$E_{UV}$$ is $$10$$ times $$E_{IR}$$ because energy is proportional to the square root of frequency.

Answer

$$E_{UV}$$ is equal to $$E_{IR}$$ because photon energy depends only on the speed of light.

Question 9

An electron and a proton travel at the same speed $$v$$ in a vacuum. The mass of the proton is approximately $$1800$$ times the mass of the electron. How does the de Broglie wavelength of the electron ($$\lambda_e$$) compare to that of the proton ($$\lambda_p$$)?

Accepted Answer

$$\lambda_e$$ is approximately $$1800$$ times $$\lambda_p$$ because wavelength is inversely proportional to mass.

Answer

$$\lambda_e$$ is approximately $$1/1800$$ times $$\lambda_p$$ because wavelength is directly proportional to mass.

Answer

$$\lambda_e$$ is equal to $$\lambda_p$$ because wavelength depends only on the particle's speed.

Answer

$$\lambda_e$$ is approximately $$\sqrt{1800}$$ times $$\lambda_p$$ because wavelength scales with kinetic energy.

Question 10

A photon of frequency $$f$$ travels from a vacuum ($$n=1$$) into a glass block ($$n=1.5$$). Which statement correctly compares the photon's speed $$v$$ and frequency $$f$$ in the glass to its values in the vacuum?

Accepted Answer

The speed decreases to $$v/1.5$$ while the frequency remains unchanged.

Answer

The speed increases to $$1.5v$$ while the frequency remains unchanged.

Answer

The speed remains unchanged while the frequency decreases to $$f/1.5$$.

Answer

The speed decreases to $$v/1.5$$ while the frequency increases to $$1.5f$$.

AP Physics 2 Unit 15 Practice Test

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