Physics 2019 Jamb Examination

Boiling is the process of rapid evaporation where a liquid transitions into its gaseous phase. During this phase change, the temperature remains constant at the boiling point (100°C for pure water at standard pressure) as the added heat is used as latent heat of vaporization to break intermolecular bonds. Thus, the water changes into steam.

Pigments follow the subtractive color theory. When blue and red pigments are mixed, they absorb most colors from the white light spectrum and reflect a combination that the human eye perceives as magenta (a purplish-red). Note: In light (additive theory), Red + Blue also equals Magenta.

1. Calculate frequency (\( f \)): The number of pulses per second is the number of holes multiplied by the revolutions per second.\[ f = \text{number of holes} \times \frac{\text{rev}}{\text{sec}} \]\[ f = 200 \times \frac{132}{60} = 200 \times 2.2 = 440 \text{ Hz} \]2. Calculate wavelength (\( \lambda \)) using \( v = f\lambda \):\[ \lambda = \frac{v}{f} = \frac{350}{440} \approx 0.795 \text{ m} \]

Pressure is defined as Force divided by Area (\( P = F/A \)). Since the man's weight (force) remains constant, the pressure is greatest when the area of contact is smallest. Standing on the toes of one foot provides the smallest possible surface area compared to standing on both feet or lying down, resulting in the maximum pressure.

Under normal conditions, gases are poor conductors because they consist of neutral molecules. However, at low pressure, there is more space for ions to accelerate without frequent collisions. When a high voltage is applied, these ions gain enough kinetic energy to ionize other molecules upon collision, allowing electricity to flow.

The neutron, a subatomic particle with no electrical charge located in the nucleus, was discovered by James Chadwick in 1932. His discovery explained the extra mass in atoms that could not be accounted for by protons alone.

The mass number (nucleon number) of an atom is defined as the sum of the number of protons and neutrons found in the nucleus. Since protons and neutrons have approximately the same mass, and electrons have negligible mass, the nucleus contains nearly all the mass of the atom.

1. Find Total Resistance (\( R_T \)) in series:\[ R_T = 200 + 500 + 1000 = 1700 \; \Omega \]2. Calculate total current (\( I \)):\[ I = \frac{V}{R_T} = \frac{6}{1700} \text{ A} \]3. Calculate potential difference (\( V_1 \)) across 200\( \Omega \):\[ V_1 = I \times R_1 = \left( \frac{6}{1700} \right) \times 200 = \frac{1200}{1700} \approx 0.7058 \text{ V} \]Rounding to two decimal places gives 0.71V.

In an AC circuit containing both an inductor and a resistor, power is only dissipated (absorbed) by the resistance. The inductor stores and releases energy but does not 'consume' it as heat. The formula for power is:\[ P = I^2 R \]Given \( I = 1 \text{ A} \) and \( R = 5 \; \Omega \):\[ P = (1)^2 \times 5 = 5 \text{ W} \]

In a semiconductor material, electrical conduction is achieved through two types of charge carriers: free electrons and holes. Holes are the absence of an electron in the valence band that acts as a positive charge carrier. At room temperature, thermal energy is sufficient to excite some electrons to the conduction band, creating electron-hole pairs.