Physics 2019 Jamb Examination

Conduction in solids, especially metals, occurs via two mechanisms: the vibration of atoms/molecules in the lattice and the movement of free electrons. In metals, the kinetic energy is rapidly transferred through the material primarily by these highly mobile free electrons, which collide with other electrons and ions, making metals excellent thermal conductors.

Gas conductivity at low pressure is often observed in discharge tubes. When the emission of electrons from the cathode occurs due to a high electric field rather than heat, it is termed cold cathode emission (III). If the electric field itself is the primary driver for extracting electrons from the metal surface, it is called field emission (IV). Hot cathode and thermionic emission refer to electron release due to high temperatures.

Sound is a mechanical longitudinal wave that requires a material medium for propagation. It travels by causing oscillations in the particles of the medium. Because air (gas), liquids (like water), and solids (like steel) all consist of particles that can transmit these vibrations, sound can pass through all three media.

Gravitational field intensity (g) is defined as the gravitational force per unit mass. At the surface of the Earth, this is numerically equivalent to the acceleration due to gravity. Using the formula:\[ g = \frac{GM}{R^2} \]Using the provided constants:\[ g = \frac{(6.7 \times 10^{-11}) \times (6 \times 10^{24})}{(6.4 \times 10^6)^2} \approx 9.8 \; \text{N/kg} \]Since the value of 'g' is explicitly given as 9.8 m/s² in the prompt, the intensity is 9.8 N/kg.

Comparing the human eye to a camera: [Image comparing anatomy of human eye and camera]
1. The Retina is the light-sensitive surface where the image forms, equivalent to the Film (or sensor).
2. The Pupil is the opening through which light enters, equivalent to the Aperture.
3. The Iris regulates the size of the pupil, equivalent to the Diaphragm which regulates the aperture size.

In the kinetic theory of gases, molecules are described as being in constant random motion and are separated by distances that are very large compared to their own size. Because of this, they have negligible intermolecular forces and will expand to fill any container they occupy.

1. Find acceleration (\( a \)):\[ a = \frac{F}{m} = \frac{6}{2} = 3 \; \text{ms}^{-2} \]2. Find final velocity (\( v \)) after 4s (starting from rest, \( u=0 \)):\[ v = u + at = 0 + (3 \times 4) = 12 \; \text{ms}^{-1} \]3. Calculate Kinetic Energy (\( K.E. \)):\[ K.E. = \frac{1}{2}mv^2 = \frac{1}{2} \times 2 \times 12^2 = 144 \; \text{J} \]

Momentum (\( p = mv \)) is a vector quantity, meaning it has both magnitude and direction. Even if the speed is constant, the direction of the car's velocity is constantly changing as it moves around the track. Therefore, the momentum vector is also constantly changing. Depending on the chosen coordinate system, the components of momentum can be positive or negative.

Using the linear expansion formula:\[ L_2 = L_1 [1 + \alpha(T_2 - T_1)] \]\[ 99.4 = 100 [1 + (2 \times 10^{-5})(T_2 - 200)] \]\[ 0.994 = 1 + 0.00002(T_2 - 200) \]\[ -0.006 = 0.00002(T_2 - 200) \]\[ T_2 - 200 = \frac{-0.006}{0.00002} = -300 \]\[ T_2 = -300 + 200 = -100^{\circ}\text{C} \]

A lead-acid battery (accumulator) consists of a lead(IV) oxide (\(\text{PbO}_2\)) positive plate and a lead (\(\text{Pb}\)) negative plate.

The electrolyte used is a dilute solution of tetraoxosulphate(VI) acid, commonly known as sulphuric acid (\(\text{H}_2\text{SO}_4\)).