Physics 12 - Chapter 12 Quiz

Name:

True/False

Indicate whether the sentence or statement is true or false.

Planck proposed that energy is radiated in bundles he called quanta. The energy of a single quantum is directly proportional to its wavelength.

At the cutoff potential, even the most energetic photoelectrons are prevented from reaching the anode.

For a given photoelectric surface, the longer the wavelength of light incident on it, the higher the cutoff potential.

In the Compton effect, high-energy photons strike a surface, ejecting electrons with kinetic energy and lower-energy photons.

Photons have momentum whose value is given by p = .

When light passes through a medium, its behaviour is best explained using its particle properties, whereas when light interacts with matter, its behaviour is best explained using its wave properties.

The diffraction of electrons revealed that particles have wave characteristics.

Electrically “excited” gases produce a continuous spectrum, while an emission spectrum or line spectrum is emitted from a heated solid.

An atom is normally in its ground state. The excited states or energy levels are the amounts of energy the atom can internally absorb.

10.

The analysis of emission and absorption spectra confirmed that there are discrete, well-defined internal energy levels within the atom.

11.

In the atom we think of the electron as a particle moving in a circular orbit whose wave properties predict its exact position and velocity.

Multiple Choice

Identify the letter of the choice that best completes the statement or answers the question.

12.

In the photoelectric effect, increasing the frequency of the light incident on a metal surface

a.	decreases the threshold frequency for the emission of photoelectrons
b.	decreases the number of photoelectrons emitted
c.	increases the threshold frequency for the emission of photoelectrons
d.	increases the kinetic energy of the most energetic photoelectrons
e.	does not affect the kinetic energy of the photoelectrons

Use Figure 1 to answer questions 13 to 15. Figure 1 shows the results of an experiment involving the photoelectric effect. The graph shows the currents observed in the photocell circuit as a function of the potential difference between the plates of the photocell when light beams A, B, C, and D, each with its own wavelength, were each directed at the photocell.

Figure 1

Graph of current versus potential difference for four different beams of light.

13.

Which of the beams of light had the highest frequency?

a.	A
b.	B
c.	C
d.	D
e.	They all had the same frequency.

14.

Which of the beams of light had the longest wavelength?

a.	A
b.	B
c.	C
d.	D
e.	They all had the same wavelength.

15.

Which of the beams of light ejected photoelectrons having the greatest momentum?

a.	A
b.	B
c.	C
d.	D
e.	They all ejected photoelectrons having the same momentum.

Use Figure 2 to answer questions 16 and 17. Here, electrons of a single energy are focused into a thin pencil-like beam incident at 90° on a very thin crystalline film of gold. On the other side of the film, a pattern of circular rings is observed on a fluorescent screen.

Figure 2

16.

This experiment provides evidence for

a.	the wave nature of matter
b.	the high speed of electrons
c.	circular electron orbits around nuclei
d.	the spherical shape of the gold atom
e.	none of these

17.

If the energy of the electrons were increased, the rings would

a.	assume the shape of an increasingly eccentric ellipse
b.	remain essentially unchanged
c.	become less intense
d.	increase in width
e.	decrease in size

Use Figure 3 to answer questions 18 to 20. Figure 3 shows a Franck–Hertz experiment performed using an accelerating potential of 8.00 V in a tube containing mercury vapour.

Figure 3

Energy levels for mercury

18.

After passing through the gas, the electrons can have energies

a.	of 4.86 eV and 6.67 eV only
b.	of 1.33 eV and 8.00 eV only
c.	of 0.84 eV, 2.40 eV, and 8.00 eV only
d.	of 3.14 eV, 1.33 eV, and 8.00 eV only
e.	in a continuum of values from 0 to 8.00 eV

19.

An electron of kinetic energy 9.00 eV collides with a mercury atom that is in the ground state. The mercury atom

a.	can only be excited to an energy of 8.84 eV
b.	can only be excited to an energy of 1.40 eV
c.	can only be excited to an energy of 0.16 eV
d.	can be excited to any of the 4.86 eV, 6.67 eV, or 8.84 eV energy levels
e.	cannot be excited by this electron

20.

A photon of energy 9.00 eV collides with a mercury atom in the ground state. The mercury atom

a.	can only be excited to an energy of 8.84 eV
b.	can only be excited to an energy of 1.40 eV
c.	can only be excited to an energy of 0.16 eV
d.	can be excited to any of the 4.86 eV, 6.67 eV or 8.84 eV energy levels
e.	cannot be excited by this photon

21.

Consider the following predictions made on the basis of the Rutherford model of the atom:

I. Electrons in an atom spiral into the nucleus.

II. The nuclei of atoms scatter a particles in a Coulomb interaction.

III. De-exciting atoms will emit light in a continuous spectrum, rather than in a discrete set of colours.

Of these predictions,

a.	only I is contradicted by observation
b.	only II is contradicted by observation
c.	only I and II are contradicted by observation
d.	only I and III are contradicted by observation
e.	none are consistent with observations

For questions 22 to 24, recall that c = 3.00

10⁸ m/s, h = 6.63

10^-³⁴ J

s, and 1 eV = 1.6

10^-¹⁹ J, and assume further that the following are energy levels for a hydrogen-like atom:

n =

... 18 eV

n = 5 ... 17 eV

n = 4 ... 15 eV

n = 3 ... 12 eV

n = 2 ... 8 eV

n = 1 ... 0 eV

22.

The ionization potential of this atom is

a.	0 V
b.	8 V
c.	10 V
d.	18 V
e.	impossible to compute from the data given

23.

The energy of the photon emitted when this atom de-excites from the state n = 3 to the state n = 2 is

a.	4 eV
b.	6 eV
c.	8 eV
d.	10 eV
e.	12 eV

24.

An electron of kinetic energy 10 eV bombards this atom in its ground state. A possible value for the kinetic energy of this electron after this interaction is

a.	0 eV
b.	2 eV
c.	8 eV
d.	18 eV
e.	28 eV