Introduction to Modern Physics

Comprehensive flashcards covering models of atomic structure, nucleus properties, radioactivity, wave-particle duality, and nuclear reactions as presented in the lecture notes.

What was the Plum Pudding Model proposed by J.J. Thompson in 1897?

An atom is a neutral particle consisting of positive charge with lumps of negative charge (electrons) within it.

According to J.J. Thompson, what was the approximate radius of an atom and the field strength on its surface?

The radius was approximately $1.0 \times 10^{-10}\,m$ and the field strength was approximately $1.4 \times 10^{11}\,V/m$.

What specific measurement did J.J. Thompson successfully obtain for the electron?

The charge to mass ratio ($e/m$).

What were the findings of the Rutherford Atomic Model regarding the nucleus?

Positive charge is concentrated in the nucleus, and the radius of the nucleus is approximately $6.9 \times 10^{-5}\,m$.

What are the two basic particles of the nucleus and their stability characteristics?

The proton is a positively charged stable particle, and the neutron is a neutral particle that is only stable when inside the nucleus.

Define Atomic Number ($Z$) and Nucleon Number ($A$).

Atomic Number ($Z$) is the number of protons in the nucleus; Nucleon Number (Mass Number, $A$) is the total number of protons and neutrons.

How is an electron volt ($eV$) defined and what is its value in Joules?

The energy gained by an electron accelerated through a potential difference of one volt, approximately $1.6 \times 10^{-19}\,J$.

What is thermionic emission and who observed it first?

The emission of free electrons from a hot metal surface, discovered by Edison in 1880.

List three properties of cathode rays.

They have rectilinear propagation, cause fluorescence, possess kinetic energy, and are deflected by both electric and magnetic fields.

In an electron gun, what is the formula for electron velocity ($v$)?

$$v = \sqrt{\frac{2eV}{m}}$$

What is 'Specific Charge'?

The charge to mass ratio ($q/m$) of a charged particle.

What is radioactivity?

The spontaneous emission of radiation from the nucleus of an atom trying to achieve a more stable configuration.

Describe the three types of radiation emitted during radioactive decay.

Alpha particles (helium nuclei), beta particles (electrons or positrons), and gamma rays (high-energy photons).

How is the half-life ($T_{1/2}$) of a radioactive isotope defined?

The time it takes for half of the radioactive material to decay.

State the mathematical law for exponential decay.

$N = N_0 e^{-\lambda t}$ where $N_0$ is the initial number of nuclei and $\lambda$ is the decay constant.

What is the relationship between half-life ($T_{1/2}$) and the decay constant ($\lambda$)?

$$T_{1/2} = \frac{0.693}{\lambda}$$

What is the Mean Life ($T$) of a radioactive sample?

The average time taken for a particle to exist, expressed as the reciprocal of the decay constant: $T = \frac{1}{\lambda}$.

Why did Classical Physics fail to explain phenomena like the photoelectric effect and X-ray production?

These phenomena are produced by the interaction of sub-atomic particles which Classical Physics could not account for.

What is the cornerstone of Quantum Physics?

Physical quantities can exist in discrete or integral values, a concept known as quantization.

State the Principle of Complementarity proposed by Bohr in 1928.

Wave and particle descriptions are complementary; both are needed to understand light, but they are never used simultaneously for a single occurrence.

What is the De Broglie Hypothesis regarding matter waves?

Free particles with rest mass ($m$) moving at non-relativistic speed ($v$) possess a wavelength: $\lambda = \frac{h}{mv}$.

What is the quantization condition for Bohr's orbits according to De Broglie?

The standing wave must satisfy $2\pi r = n\lambda$ where $n = 1, 2, 3, \dots$

Define isotopes.

Variants of a chemical element that have the same number of protons but a different number of neutrons.

Compare the penetration power of alpha, beta, and gamma radiation.

Alpha is weakly penetrating (stopped by paper), beta is more penetrating (stopped by aluminum), and gamma is most penetrating (stopped by thick lead or concrete).

What is the difference between nuclear fission and nuclear fusion?

Fission splits a large nucleus into two smaller ones (chain reaction), while fusion combines two small nuclei to form a larger one (requires high temperature/pressure).