Physics 2025 Jamb Examination

Short-sightedness (myopia) occurs when light rays from distant objects focus in front of the retina. To correct this, a diverging (concave) lens is used to spread the rays before they enter the eye, allowing them to focus exactly on the retina. For a person with a far point at a finite distance \(d\), the correcting lens must have a focal length \(f = -d\) to bring distant objects to that far point. Thus, a diverging lens of focal length 95 cm is required.

Electrical energy (E) is calculated as the product of power (P) and time (t). To get the result in kilowatt-hours (kWh), power must be in kilowatts (kW) and time in hours. \[ P = 150\, \text{W} = 0.15\, \text{kW} \] \[ t = 336\, \text{hours} \] \[ E = P \times t = 0.15 \times 336 = 50.40\, \text{kWh} \]

Magnetic shielding is the process of diverting magnetic field lines around a sensitive area. Materials with high magnetic permeability, such as soft iron or mu-metal, are used because magnetic field lines prefer to travel through these materials rather than through the air or other non-magnetic substances (like copper or aluminum). This effectively 'screens' the interior from external magnetic fields.

Geiger-Muller counters, scintillation chambers, and film badges are all designed to detect ionizing radiation (alpha, beta, or gamma rays). An electrophorus, however, is a simple manual capacitive generator used to produce electrostatic charges via induction; it has no capability for detecting nuclear radiation.

The wet Leclanche cell consists of a zinc anode and a carbon cathode surrounded by manganese dioxide (the depolarizer). These components are immersed in a solution of ammonium chloride (\(NH_4Cl\)), which acts as the electrolyte allowing ions to move between the electrodes.

When the magnetic flux through a conductor changes, a potential difference is produced. This generated voltage is specifically referred to as the induced electromotive force (e.m.f.). While it can cause an induced current to flow if there is a closed circuit, the 'electricity' generated at the source is the e.m.f.

In the International System of Units (SI), there are seven base units from which all other units are derived. The Ampere (unit of electric current) is one of these fundamental base units. Joule, Volt, and Ohm are all derived units defined in terms of the base units.

The net force ($F_{\text{net}}$) is the weight ($W$) minus the total upward forces (upthrust ($U$) and viscous drag ($F_{\text{drag}}$)). This net force causes the acceleration ($a$) according to Newton's second law ($F_{\text{net}} = ma$):\[ F_{\text{net}} = W - U - F_{\text{drag}} \]\[ ma = (m \times g) - U - F_{\text{drag}} \]
Substituting the given values:\[ (10\,\text{kg}) \times a = (10\,\text{kg} \times 10\,\text{m/s}^2) - 10\,\text{N} - 15\,\text{N} \]\[ 10a = 100\,\text{N} - 25\,\text{N} \]\[ 10a = 75\,\text{N} \]\[ a = \frac{75\,\text{N}}{10\,\text{kg}} \]\[ a = 7.5\,\text{m/s}^2 \]

A wavelength (\(\lambda\)) is defined as the distance between two successive points in a wave that are in the same phase. This includes the distance from one crest to the next, or from one trough to the next.

In the visible light spectrum (ROYGBIV), Red has the longest wavelength and the lowest frequency. As we move toward the violet end of the spectrum, the wavelength decreases and the frequency increases.