Physics Secondary 3 Review: Radiation, Electrostatics, and Electricity

Comprehensive practice flashcards covering the structure of the atom, quantum phenomena, electrostatics, and current electricity as detailed in the South Sudan Secondary Physics Student's Book 3.

Who was the first person to hypothesize that matter is made of tiny indivisible units called atoms, meaning 'unable to be cut or divided'?

Democritus

What is the 'law of definite proportions' as formulated by John Dalton?

A chemical compound always contains the same proportion of a particular element.

Which scientist discovered the electron in 1897 and proposed the plum pudding model of the atom?

J.J. Thomson

What was the conclusion of Ernest Rutherford's alpha particle scattering experiment regarding the structure of an atom?

An atom consists of a small, positively charged nucleus at the centre which carries almost the entire mass of the atom.

According to the Bohr model, what are the definite circular paths where electrons revolve around the nucleus called?

Orbits or shells

What is the state of an electron when it attains its lowest energy level?

Ground state

What is the formula to calculate the energy for an electron in an orbital with quantum number $n$ in Bohr's model?

$$E(n) = -\frac{1}{n^2} \times 13.6 \text{ eV}$$

How is 'excitation' defined in the context of atomic energy levels?

The process by which an electron moves from a lower energy level to a higher energy level when it gains a specific amount of energy.

What is Planck's constant ($h$) used to relate the energy of radiation to its frequency?

$$6.63 \times 10^{-34} \text{ Js}$$

What is the name of the constant $R = 1.097 \times 10^7 \text{ m}^{-1}$ found in the hydrogen spectrum equations?

Rydberg constant

Which hydrogen spectral series involves transitions to the $n=2$ level and includes lines in the visible spectrum?

Balmer series

What is the definition of ionisation?

The process of giving an electron enough energy to remove it completely from the atom.

What is the primary function of the phosphorous coating on the inside of a fluorescent tube?

It absorbs UV photons and undergoes excitation to emit many lower energy photons in the range of visible light.

What is the photoelectric effect?

The process of removing electrons from a metal surface by using radiation.

What is 'threshold frequency' ($f_0$)?

The minimum frequency of radiation below which no emission of photoelectrons occurs for a given metal surface.

How many Joules are equivalent to one electron volt ($1 \text{ eV}$)?

$$1.6 \times 10^{-19} \text{ J}$$

Define the 'work function' ($W$) of a metal.

The minimum energy required to completely remove an electron from the metal surface without giving it any additional kinetic energy.

State Einstein's equation for the photoelectric effect.

$$hf = W + \frac{1}{2}mv^2_{\text{max}}$$

What happens to the number of ejected photoelectrons when the intensity of radiation is increased?

The number of ejected photoelectrons increases because it is directly proportional to intensity.

Define 'stopping voltage' ($V_s$).

The retarding voltage at which no electrons are able to reach the anode, making the photocurrent zero.

What type of photocell generates an electromotive force between terminals when light shines on it without requiring a battery?

Photovoltaic cell

State the de Broglie wavelength equation.

$$n = \frac{h}{mv}$$

What are the three main subatomic particles in an atom and their respective charges?

Protons (positive), Electrons (negative), and Neutrons (no charge).

State the basic law of electrostatics.

Like charges repel while unlike charges attract.

What is the difference in the resulting charge between charging by induction and charging by contact?

Induction results in a charge opposite to the charging rod, while contact/conduction results in the same charge.

State Coulomb's Law.

The force of attraction or repulsion between two charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

What is the mathematical formula for Coulomb's Law?

$$F = k \frac{Q_1 Q_2}{r^2}$$

What is the value of the constant $k$ in Coulomb's Law for charges in free space?

$$9 \times 10^9 \text{ Nm}^2\text{C}^{-2}$$

What is a gold leaf electroscope used for?

A sensitive instrument used for detecting and testing small electric charges.

What is 'earthing'?

The process of connecting a charged body to the earth using a conducting material to neutralize it.

Define electrical resistance.

The opposition offered by a conductor to the flow of current through it.

State Ohm's Law.

The current ($I$) flowing in a conductor is directly proportional to the potential difference ($V$) across it, provided temperature and other physical conditions remain constant.

What are ohmic conductors?

Conductors that obey Ohm's Law and produce a straight-line graph for $V$ against $I$.

How is the resistance of a carbon resistor indicated?

By four coloured bands painted around it representing digits, the multiplier (power of ten), and tolerance.

What is the formula for the effective resistance ($R_s$) of resistors connected in series?

$$R_s = R_1 + R_2 + \text{ ...} + R_n$$

What is the formula for the effective resistance ($R_p$) of resistors connected in parallel?

$$\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \text{ ...} + \frac{1}{R_n}$$

State Kirchhoff's Current Law (KCL).

The algebraic sum of all the currents entering and leaving a node must be equal to zero.

State Kirchhoff's Voltage Law (KVL).

In any closed loop network, the total voltage around the loop is equal to the sum of all the voltage drops within the same loop.

How does the resistance ($R$) of a straight conductor relate to its length ($L$) and cross-sectional area ($A$)?

It is directly proportional to length and inversely proportional to cross-sectional area ($R = \rho \frac{L}{A}$).

What is the SI unit of resistivity ($\rho$)?

Ohm-metre ($\text{Ω m}$)