Physics 2019 Jamb Examination

To determine the direction of the magnetic field around a straight conductor, we use Maxwell's Right-Hand Grip Rule. Point your thumb downwards (direction of the current); your fingers curl in a clockwise direction when viewed from above. If you are at a point due North of the wire, the clockwise circular field lines will be moving towards the West at that specific location.

A gold-leaf electroscope requires leaves that are extremely thin and light so they can easily diverge even with a small amount of electrostatic force.

While gold is traditional because it is highly malleable, aluminium is also used because it can be beaten into very thin, lightweight foils (high malleability) while remaining a good conductor of electricity.

In a typical stress-strain graph for a metal wire: the initial linear portion (up to a point often labeled J or K) represents the elastic region where Hooke's Law is obeyed. At the elastic limit (J), the material begins to deform plastically. Point K is usually the yield point where the material flows without additional stress, and point L typically represents the breaking (fracture) point.

1. Find the equivalent capacitance (\( C_T \)) for series capacitors:\[ \frac{1}{C_T} = \frac{1}{C_1} + \frac{1}{C_2} = \frac{1}{3} + \frac{1}{6} = \frac{2+1}{6} = \frac{3}{6} \]\[ C_T = 2\mu\text{F} = 2 \times 10^{-6}\text{F} \]2. Calculate total charge (\( Q \)) using \( Q = CV \):\[ Q = (2 \times 10^{-6}\text{F}) \times 400\text{V} \]\[ Q = 800 \times 10^{-6}\text{C} = 8 \times 10^{-4}\text{C} \]In a series circuit, this charge \( Q \) is the same across all capacitors.

1. Calculate wave speed (\( v \)):\[ v = \frac{\text{Distance}}{\text{Time}} = \frac{50\text{cm}}{2\text{s}} = 25\text{cm/s} \]2. Identify wavelength (\( \lambda \)): The distance between successive crests is the wavelength, so \( \lambda = 5\text{cm} \).
3. Calculate frequency (\( f \)) using the wave equation:\[ v = f\lambda \implies f = \frac{v}{\lambda} \]\[ f = \frac{25}{5} = 5\text{Hz} \]

A thermocouple operates on the principle that the electromotive force (e.m.f.) produced is directly proportional to the temperature difference between the junctions (for linear ranges).



We can use a simple ratio:\[ \frac{V_1}{T_1} = \frac{V_{\text{max}}}{T_{\text{max}}} \]\[ \frac{4\text{mV}}{100^{\circ}\text{C}} = \frac{10\text{mV}}{T_{\text{max}}} \]\[ T_{\text{max}} = \frac{10 \times 100}{4} = 250^{\circ}\text{C} \]

According to Faraday's Law of Electromagnetic Induction, an electromotive force (e.m.f.) is induced in a circuit whenever there is a change in the magnetic flux linked with the circuit.

An alternating current (AC) continuously changes its magnitude and direction, which creates a continuously varying magnetic field around the conductor. This varying field ensures a constant change in flux, inducing voltage in nearby conductors.

Limiting friction is the maximum static friction that must be overcome to start motion. It depends only on the nature of the surfaces in contact (roughness, materials) and the normal reaction force. It is independent of the surface area and, crucially, independent of the relative velocity (since the surfaces are not yet in relative motion). This matches statement II.

During a phase change, such as melting (solid to liquid), the energy provided is 'latent' (hidden). Instead of increasing the kinetic energy of the molecules (which would increase the temperature), the energy is consumed to break the intermolecular bonds and overcome the attractive forces that maintain the rigid structure of the solid.

The assumption 'Heat lost = Heat gained' relies on the system being thermally isolated so that no heat is lost to the surroundings. Lagging the calorimeter (I) with an insulating material prevents heat exchange with the environment, making the assumption valid. Weighing the equipment (III) is necessary for the calculation itself but doesn't validate the physical assumption of zero heat loss.