Physics 2023 Jamb Examination

The Bohr model, proposed by Niels Bohr in 1913, was the first to suggest that electrons move in fixed, circular orbits (shells) around the nucleus, each with a specific energy level.

Unlike the Rutherford model, which suggested electrons could be anywhere outside the nucleus, the Bohr model quantised the orbits, meaning electrons can only exist in these specific levels and must gain or lose energy to move between them.

The Nickel-Iron (NiFe) accumulator, also known as the Edison battery, is an alkaline storage battery. It uses potassium hydroxide (KOH) solution as the electrolyte. Unlike lead-acid batteries that use sulphuric acid, the NiFe battery is very robust and can withstand overcharging or being left discharged for long periods without significant damage.

Insulators are materials that do not allow electric current to flow through them easily because their electrons are tightly bound to their atoms. Rubber is a classic example of an insulator used to coat electrical wires for safety. Silver and copper are excellent conductors, while water (unless exceptionally pure) usually contains ions that allow it to conduct electricity.

In physics, a couple consists of two parallel forces that are equal in magnitude, opposite in direction, and do not share the same line of action. A couple produces a turning effect or torque without translation. Turning a steering wheel with both hands, using a cross-wrench for lug nuts, and twisting a screwdriver all involve applying two equal and opposite forces to create rotation, making all the listed options valid examples.

According to the fundamental law of electrostatics, opposite charges attract each other. This means the positively charged particle will experience a force pulling it toward the negative particle, and the negative particle will experience a force pulling it toward the positive particle. Therefore, the force acting on the positive particle is directed toward the negative one.

This phenomenon is explained by the relationship between adhesion and cohesion. Adhesion is the force of attraction between different types of molecules (water and wood), while cohesion is the attraction between similar molecules (water and water). When water spreads out to 'wet' a surface, it indicates that the adhesive forces between the water and the surface are stronger than the cohesive forces holding the water droplet together.

The angle of dip (or magnetic inclination) is the angle that the Earth's magnetic field lines make with the horizontal plane. At the magnetic equator, the magnetic field lines are perfectly horizontal, so the angle of dip is \(0^{\circ}\). At the magnetic poles, the field lines are vertical, pointing straight into or out of the Earth, making the angle of dip \(90^{\circ}\).

In the 'Divided Touch' method of magnetisation, two magnets stroke a steel bar starting from the centre and moving outwards to the ends. The end of the bar where the magnet leaves will always acquire a polarity opposite to the stroking pole. Since the south-poles (S) of both magnets are being used to stroke outwards toward T and V, both ends T and V will acquire the opposite polarity, which is North (N).

The primary difference between an AC generator and a DC generator is the method of connecting the rotating armature to the external circuit. [Image comparing slip rings and split rings in generators] An AC generator uses slip rings, which allow the current to alternate. A DC generator uses a split-ring commutator, which reverses the connection to the external circuit every half-turn to ensure the current flows in only one direction. To convert an AC generator to DC, you must replace the slip rings with split rings.

Modern physics refers to concepts developed from the early 20th century onwards, including Quantum mechanics, Special relativity, and Nuclear physics. Classical mechanics (also known as Newtonian mechanics) deals with the motion of macroscopic objects at speeds much slower than the speed of light and was developed primarily by Isaac Newton and his predecessors, making it 'Classical' rather than 'Modern'.