Q: A blackbody at temperature $$T$$ emits radiation with a peak wavelength $$\lambda_{\text{peak}}. $$According to Wien’s Law, what happens to $$\lambda_{\text{peak}} if $$the temperature is doubled?

$$\lambda_{\text{peak}} is $$halved

Question 1

Which experiment provided the first direct evidence that atoms have internal structure and are not indivisible, as previously thought?

Accepted Answer

Rutherford’s gold foil experiment

Question 2

A blackbody at temperature $$T$$ emits radiation with a peak wavelength $$\lambda_{	ext{peak}}. $$According to Wien’s Law, what happens to $$\lambda_{	ext{peak}} if $$the temperature is doubled?

Accepted Answer

$$\lambda_{	ext{peak}} is $$halved

Question 3

Which of the following statements about atomic spectra is correct?

Accepted Answer

Each element has a unique discrete emission spectrum that acts as a fingerprint.

Question 4

In the Millikan oil-drop experiment, the charge on an oil droplet is found to be $$4.8 	imes 10$$^{-19}$$ C. What does this result imply?

Accepted Answer

The charge is a multiple of the elementary charge $$e$$

Question 5

Which of the following best describes the main finding of J. J. Thomson’s cathode ray experiments?

Accepted Answer

Cathode rays are composed of identical negatively charged particles, later called electrons.

Question 6

A hot filament emits a continuous spectrum of light. What is the physical origin of this spectrum?

Accepted Answer

Blackbody radiation due to the thermal motion of charged particles

Question 7

The Balmer formula for the hydrogen emission spectrum is $$\frac{1}{\lambda} = 91.18\,	ext{nm}^{-1} \left( \frac{1}{2^2$} - \frac{1}{n^2$} ight)$$ for $$n \u003e 2. $$What does this formula empirically describe?

Accepted Answer

The wavelengths of visible spectral lines emitted by hydrogen

Question 8

In Rutherford’s model of the atom, what occupies most of the volume of the atom?

Accepted Answer

Empty space

Question 9

A hydrogen atom has an energy of $$-13.6 eV in $$its ground state. What is the minimum energy required to ionize it?

Accepted Answer

$$13.6 eV$$

Question 10

Which of the following is NOT explained by classical physics, leading to the development of modern physics?

Accepted Answer

The stability of atoms

Question 11

A spectrometer uses a diffraction grating to analyze light. What is the main advantage of using a curved diffraction grating in a spectrometer?

Accepted Answer

It focuses the spectrum onto the photodetector for better resolution.

Question 12

Which statement about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 13

The energy of an electron in a hydrogen atom is $$-2.17 	imes 10$$^{-18}$$ J. What is this energy in electron volts (eV)? (Given 1$$\,	ext{eV} = 1.60 	imes $$10^{-19} J)$$

Accepted Answer

$$-13.6 eV$$

Question 14

Which of the following best describes the role of neutrons in the atomic nucleus?

Accepted Answer

They provide additional 'glue' to hold the nucleus together.

Question 15

A 1.0-μm-diameter oil droplet with a density of $$860\,	ext{kg/m}^3$$ acquires 10 extra electrons. What is the magnitude of the charge on the droplet?

Accepted Answer

$$1.60 	imes 10$$^{-18}$$ C

Question 16

Which of the following is a correct statement about the relationship between emission and absorption spectra of a gas?

Accepted Answer

Every wavelength absorbed by the gas is also emitted, but not every emitted wavelength is absorbed.

Question 17

In Thomson’s crossed-field experiment, a charged particle passes undeflected through perpendicular electric and magnetic fields. What is the condition for this to occur?

Accepted Answer

$$v = \frac{E}{B}$$

Question 18

What is the energy (in joules) of an alpha particle with a kinetic energy of $$8.3$$ MeV? ($$1\,	ext{eV} = 1.60 	imes 10$$^{-19}$$ J)

Accepted Answer

$$1.33 	imes 10$$^{-12}$$ J

Question 19

Which of the following is a real-world application that relies on the properties of atoms as described in modern physics?

Accepted Answer

Atomic clocks used in global timekeeping

Foundations of Modern Physics: Atomic Structure, Spectra, and the Limits of Classical Physics

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