## The temperature coefficient of resistance for a semiconductor

- Zero
- Infinity
- Positive
- Negative

Correct Option: (D)

The temperature coefficient of resistance for a semiconductor is negative. This means that the resistance of a semiconductor decreases as the temperature increases.

## Of the three chief kinds of magnetic materials (diamagnetic, paramagnetic, and ferromagnetic) which are used to make permanent magnets

- Only diamagnetic
- Only ferromagnetic
- Only paramagnetic
- Only paramagnetic and ferromagnetic

Correct Option: (B)

Permanent magnets are made of ferromagnetic materials because they have permanent magnetic moments that are aligned in the same direction.

The other materials such as diamagnetic and paramagnetic materials have randomly oriented magnetic moments and cannot produce a permanent magnetic field.

Type of Material | Response to a Magnetic Field | Permanent Magnet? |
---|---|---|

Diamagnetic | Weakly repelled | No |

Paramagnetic | Weakly attracted | No |

Ferromagnetic | Strongly attracted | Yes |

## Consider radio waves (r), visible light (v), infrared light (i), x-rays (x), and ultraviolet light (u). In order of increasing frequency, they are

- r, v, i, x, u
- r, i, v, u, x
- i, r, v, u, x
- i, v, r, u, x

Correct Option: (B)

The correct increasing frequency order is r, i, v, u, x.

## Maxwell’s equations predict that the speed of light in free space is

- Independent of frequency
- An increasing function of frequency
- The decreasing function of frequency
- A function of the distance from the source

Correct Option: (A)

Maxwell’s equations predict that the speed of light in free space is independent of frequency.

This means that light of all frequencies from radio waves to gamma rays travels at the same speed in a vacuum.

## In a photoelectric effect experiment at a frequency above cut off the stopping potential is proportional to

- The energy of the least energetic electron after it is ejected
- The energy of the most energetic electron after it is ejected
- The energy of the least energetic electron before it is ejected
- The energy of the most energetic electron before it is ejected

Correct Option: (B)

The stopping potential in the photoelectric effect experiment is proportional to the energy of the most energetic electron after it is ejected.

In other words, the stopping potential is equal to the maximum kinetic energy of the ejected electrons.

## The probability that a particle is in a given small region of space is proportional to

- Its energy
- Its momentum
- The frequency of its wave function
- The square of the magnitude of its wave function

Correct Option: (D)

The probability that a particle in a given small region of space is proportional to the square of the magnitude of its wave function.

\[ \mathrm{P(x) = |\Psi(x)|^{2}} \]

## The ground state energy of an electron in a one-dimensional trap with zero potential energy in the interior and infinite potential energy in the walls is

- Zero
- Increases with temperature
- Decreases with temperature
- Independent of temperature

Correct Option: (D)

The ground state energy of an electron in a one-dimensional trap with zero potential energy in the interior and infinite potential energy in the walls is independent of temperature.

The energy of the ground state wave function is given by the following equation

\[ \mathrm{E_{n} = \frac{n^{2}h^{2}}{8mL^{2}}} \]

\[ \mathrm{E_{1} = \frac{h^{2}}{8mL^{2}}} \]

## The Pauli’s exclusion principle is obeyed by

- All particles
- All charged particles
- All particles with spin quantum numbers are 1
- All particles with spin quantum numbers are 1/2

Correct Option: (D)

The Pauli exclusion principle is obeyed by all particles with half-integer spin quantum numbers such as electrons, protons, neutrons, and quarks.

Particles with integer spin quantum numbers such as photons and pions do not obey the Pauli exclusion principle.

## Photons in a laser beam have the same energy, wavelength, polarization direction, and phase because

- All come from the same atom
- The lasing material has only two quantum states
- All photons are alike, regardless of their emission source
- Each is produced in an emission that is stimulated by another

Correct Option: (D)

Photons in a laser beam have the same energy, wavelength, polarization direction, and phase because each is produced in an emission that is stimulated by another.

## The energy gap (in eV) between the valence and conduction bands of an insulator is of the order of

- 10
- 0.1
- 10
^{-19} - 0.001

Correct Option: (A)

The energy gap between the valence and conduction bands of an insulator is typically of the order of 10 eV.

This means that an electron in the valence band needs to gain at least 10 eV of energy in order to jump to the conduction band.

That amount of energy is very large and due to this insulators are not conductive.